Download - Roof coverings in schools - Archive · roof coverings Roof decks are generally either: concrete, profiled metal (steel or aluminium) or timber sheeting. The following factors must

Roof coverings in schools

FIVE

Acknowledgments

We are grateful to the following individuals andorganisations that have contributed to thisdocument:

Richard Parker (Lead Author), Morgan Professional ServicesMark Cleverly, EC HarrisRita Singh, Construction Products Association

A number of other organisations kindly donatedtheir time to assist in the production of thisguidance. A full list can be found on page 53.

We are also grateful to the following membersof the Standard Specifications, Layouts andDimensions (SSLD) Forum who have helpedshape the broad approach to standardisation in this and other guidance documents in this series:

Mukund Patel, DCSF (SSLD Chair)Alan Jones, DCSF (SSLD Policy Lead)Ian Morris, Atkins (SSLD Project Manager)Beech Williamson, Partnerships for SchoolsStephen Reffitt, Atkins Mark Cleverly, EC HarrisPaul Foster, EC HarrisMichal Cohen, Walters and Cohen Architects

Karen Rogers, Walters and Cohen ArchitectsChristian Held, Penoyre and Prasad ArchitectsSunand Prasad, Penoyre and Prasad Architects Linton Ross, Feilden Bradley Clegg ArchitectsPeter Clegg, Feilden Bradley Clegg ArchitectsPaul Hetherington, AlumascRichard Parker, Morgan Professional ServicesAndrew Williams, BREBill Healy, Build OffsiteRichard Ogden, Build OffsiteMike Entwisle, Buro HappoldRita Singh, Construction Products AssociationMichael Ankers, Construction ProductsAssociationBea Etayo, Fulcrum ConsultingPeter Blunt, Mtech GroupMartin Goss, Mtech GroupDavid Mackness, SCAPE System Build LtdMartin Lipson, 4PsMairi Johnson, CABERichard Saxon, CBEPeter Woolliscroft, OGCRichard Brindley, RIBAVic Ebdon, Devon County CouncilDon Bryson, Manchester City CouncilKevin Kendall, Nottinghamshire County Council

Roof coverings in schools 1

Contents

1 Introduction 2

Who this guidance is for 2How the guidance should be used 2Background to Standard Specifications, Layouts and Dimensions (SSLD) 4Aims and scope of this guidance 5

2 Key performance requirements 6

Materials 6

Roof construction 11

Green roofs 20

Thermal performance 21

Acoustics 23

Performance in fire 25

Environmental 27

Health, safety, maintenance and guarantees 34

Cost comment 37

3 Performance specifications and examples 38

Minimum performance requirements 39Examples of roof covering solutions 40

4 References 48

Typical constructions 48Thermal 49Acoustics 49Fire 50General requirements 50Trade association links 51

2 Standard specifications, layouts and dimensions

Introduction

This guidance is one of a series of

Standard Specifications, Layouts and

Dimensions (SSLD) notes produced to

inform the Building Schools for the

Future (BSF) programme.

Who this guidance is for• Teachers and governors acting as clients for

school capital projects.

• Local authority officers responsible forprocuring school capital projects.

• Diocesan building officers.

• Local authority and private sector schooldesigners and specifiers.

• Manufacturers and suppliers.

• Contractors.

How the guidance should be usedThis guidance sets out the standards ofperformance for roof coverings in the BuildingSchools for the Future (BSF) programme andshows through some examples how they mightbe delivered. It is one of a number ofpublications on various building elementswithin the SSLD series. The aim is todisseminate best practice and avoid‘reinventing the wheel’ every time a schoolbuilding is designed, so that consistently highquality environments can be delivered, offeringbest whole-life value for money.


School building clients, their professionaladvisers, contractors and their supply chainsshould use this guidance to inform theirdecisions on roof coverings at the early stagesof a project’s development – whether newbuild, extension or refurbishment – at RIBAStages A-F.

To help encourage the take up of theseperformance specifications, this guidance willbecome the standard in BSF programmedocumentation and the Government willexpect it to be adopted in the majority ofsituations where it is reasonable andappropriate to do so.

While we would expect projects to comply withthe standards, other solutions – possibly basedon new products or technologies, or reflectinglocal factors – may equally comply with theperformance specification and could be used.We do not want to stifle innovation by beingtoo prescriptive.

It will be for users to exercise their own skilland expertise in deciding whether a standardor example shown in this document isreasonable and appropriate for their owncircumstances. This guidance does not affectobligations and liabilities under the lawrelating to construction and building.

PHOTO REDACTED DUE TO THIRD PARTY RIGHTS OR OTHER LEGAL ISSUES


Though principally aimed at secondary schoolbuilding projects delivered through the BSFprogramme, the specifications and examplesmay also apply to other educational buildings.

We will keep this guidance under review andupdate it as necessary to reflect thedevelopment of new products, processes andregulations. There is a web-based version at:www.teachernet.gov.uk/schoolbuildings

Background to StandardSpecifications, Layouts andDimensions (SSLD) The BSF programme offers a uniqueopportunity over the next 10-15 years totransform our secondary schools, providinginnovative learning environments that willinspire pupils to achieve more. High quality,modern school buildings will help to raisestandards and play a crucial part in theGovernment’s programme of educationalreform.

With the huge increases in funding associatedwith this programme, there is considerablescope for using standardised specifications,layouts and dimensions to speed up design andconstruction, reduce whole-life costs anddeliver consistently high quality and bettervalue school buildings. Standardisation willsupport the use of more off-site fabrication andmodern methods of construction, which shouldhelp to improve health and safety performance,reduce waste and deliver more sustainablesolutions. For the supply industry, beinginvolved in standardisation will help todemonstrate market leadership – and help firmsreduce risk and increase sales, profitability, andmarket size.

The examples in this document and the othersin the SSLD series have been developed basedon extensive consultation under the auspices ofthe SSLD Forum. Set up by the Department forChildren Schools and Families (DCSF), thisforum represents key stakeholders in thebuilding design, research, contracting, andsupply industry communities, as well as localauthority construction client bodies.PHOTO REDACTED DUE TO THIRD PARTY RIGHTS OR OTHER LEGAL ISSUES


Aims and scope of this guidanceThis document provides standard performancespecifications and some examples to help withthe choice of roof coverings in BSF secondaryschools.

Specifically it:

• Sets out minimum standards of performanceand quality expected by the DCSF.

• Provides design guidance for projectdesigners formulating technical specifications.

• Standardises roof covering types so thatefficiencies and economies of scale can begenerated within the supply chain.

• Enables caretakers and facilities managers tomanage roofs.

It is structured as follows:

Section 2

The generic performance characteristics of roofcoverings in secondary schools.

Section 3

A summary of the minimum performancerequirements for roof coverings, together withsome design examples and advice.

Section 4

References to relevant European, BritishStandards, DCSF and other design guidance.

This document is not a roofing design guide. Itspurpose is to make clear the clientrequirements, the minimum standards to bereached or exceeded and what is expected toprovide the best roof coverings for BSF andother school projects.

The document has been produced to informrather than replace detailed projectspecifications. Descriptions are given in genericterms and are not intended to promote theproducts of specific manufacturers. Contractorsand specifiers should consult with relevantmanufacturers to establish which products areappropriate and compliant.



Key performance requirements

The following generic key performance

requirements set the minimum

standards that DCSF would expect to

be adopted in BSF schools wherever

it is reasonable and appropriate.

Section 3 summarises the minimum

performance requirements for roof

coverings and provides some examples

that address them.

The primary function of the roof is to provideprotection from the weather and give adequateprovision for thermal insulation, fireperformance and sound insulation. Roof finishesmust be considered by all parties at an earlydesign stage to ensure the work is carried outsafely and cost effectively; and that all detailsand potential conflicts are anticipated andproperly provided for.

Materials

Coverings

The types of roof coverings can be groupedinto two main categories defined by theirsupport systems.

1. Continuously supported roof coverings:

Roof coverings with no structural propertiesfully supported on a roof deck.

• Reinforced bitumen membranes.

• Polymeric single ply membranes.

• Mastic asphalt.

• Liquid waterproofing systems.

• Malleable sheet metal roofing.


2. Discontinuously supported roof coverings:

Roof coverings with structural propertiessupported on rafters or purlins.

• Slating/tiling.

• Profiled sheeting.

• Insulated panels.

Roof deck – continuously supported roof coverings

Roof decks are generally either: concrete,profiled metal (steel or aluminium) or timbersheeting. The following factors must apply:

• The deck must have a minimum of 60 years’ life.

• The roof covering manufacturers’recommendations for the roof deck must befollowed, including but not limited to: profiledmetal deck suitable for applied load and anyrequirements for timber sheathing, surfacefinish, minimum timber sheet thickness andgrade, fixing locations, requirements forisolation layers and vapour control layers.

• Fasteners must be corrosion resistant anddesigned to withstand site wind loads to BS 6399-2 and be to manufacturers’recommendations.

• Expansion requirements must be obtainedfrom the roof deck manufacturer.

• The construction of the roof deck must beconsidered with regard to safety inconstruction. See ‘Health and safety’ section,page 34.

• The roof deck must resist dead, live and windloads.

• Metal decks must comply with BS 5950-6, BS EN 10147 (galvanised steel) and BS EN 485-2 (aluminium).



• Wood-based panels used as roof deckingmust as a minimum be either OSB/3 to BS EN300, type P5 particleboard to BS EN 312, orplywood (Technical Class Humid) to BS EN636. All wood-based panels used as deckingmust comply with the performancecharacteristics and marking requirements forwood-based panels used as structural roofdecking, as specified in BS EN 13986.

Roof deck – discontinuously supported roof coverings

Roof decks/sarking are generally: timber trusses,battens or timber sheeting for slates/tiles, andmetal purlins for metal clad roof systems. The following factors must apply:

Generally:

• The deck must have a minimum of 60 years’life.

• Expansion requirements must be obtainedfrom the roof deck manufacturer.

Additionally for slates and tiles:

• Timber sarking may be required above timberroof trusses if the school is located in areas ofsevere wind or rain. Roof coveringmanufacturers’ recommendations should besought.

• Timber battens on tiled or slate roofs must notbe less than those stated in BS 5534, Table 1.

• Counter battens on tiled or slate roofs shouldbe sufficient to provide a ventilation gap asrecommended in BS 5250 and/or to providedrainage path beneath the battens.

• The roof covering manufacturer’srecommendations for the roof deck must befollowed, including but not limited torafter/battens or purlin sizes and anyrequirements for timber sheathing, minimumtimber sheet depths and grade, fixinglocations, requirements for isolation layers andvapour control layers.

• Gable details must be developed inconjunction with requirements for externalwall structural support and claddingrequirements.

• Fasteners must be corrosion resistant anddesigned to withstand site wind loads.

• The construction of the roof deck must beconsidered with regard to safety inconstruction. See ’Health and safety’ on page 34.

• Wood-based panels used as roof deckingmust as a minimum be either OSB/3 to BS EN300, type P5 particleboard to BS EN 312, orplywood (Technical Class Humid) to BS EN636. All wood-based panels used as deckingmust comply with the performancecharacteristics and marking requirements forwood-based panels used as structural roofdecking as specified in BS EN 13986.

• Timber and timber products for structural usemust comply with BS 5268-2.


Additionally for metal roof cladding:

• Roof purlins, deflections and tolerances mustbe in accordance with the guidelines set outin Best practice for the specification andinstallation of metal cladding and secondarysteelwork (SCI publication p346 – 2006).

• The panel manufacturer’s recommendationsmust be followed regarding performance, tomeet the specification requirements.

• The profiled roof covering manufacturer’srecommendations must be followed,including any requirements for isolation layersand vapour control layers.

• Fasteners must be corrosion resistant anddesigned to withstand site wind loads.

• The construction of the roof deck must beconsidered with regard to safety inconstruction. See ‘Health and safety’ on page 34.

Vapour control layer

During cold external conditions, vapour controllayers reduce the diffusion of moisture vapourfrom the habitable space below and into theroof construction, where it could damagecomponents or reduce the efficiency of theinsulation. Proprietary vapour control layers areavailable and should have a design lifeequivalent to the roof covering. All laps must bebonded or sealed as appropriate andpenetrations effectively sealed asrecommended by the vapour control layermanufacturer.

The principles for the control of condensation inbuildings must be taken from BS 5250, 2002:Control of condensation in buildings. This statesthat a vapour control layer should extend overthe whole of the element into which it isincorporated and must be integrated with andsealed to adjoining elements, such as masonry,up-stands and glazing systems, and to any VCLin those elements.

The risk of condensation forming within theroof construction needs to be considered andcalculated. A steady state calculation isundertaken to check that no surfacecondensation will occur on any of the roofingcomponents, based on an external temperatureof -5°C. This allows a comparison between theactual temperature at any point in aspecification and the dew point temperature ofthe internal condition. If the actual temperatureat that point is lower than the dew pointtemperature, condensation will occur.

Sealants are not to be the sole line of defenceagainst water vapour penetration.


Underlay

Additional to the vapour control layer, anunderlay must be provided for discontinuouslysupported slate or tiled roofs, which should:

• Provide a barrier to minimise the wind upliftload on the slates or tiles.

• Provide a secondary barrier to the ingress ofwind driven snow and dust.

• Transport into the roof drainage system anymoisture in the batten space.

• Provide temporary (i.e. less than 3 months)weather protection, including rain impactresistance, before installation of the primaryroof covering.

• Withstand tenting.

• Withstand fixing penetrations: nail holesthrough underlays should not be enlarged,due to shrinkage.

Insulation

Additional to the roof covering, the roof systemmust also include insulation. Thermal insulation,however, is rarely a factor affecting the choiceof the roof type, since the normal methods ofproviding it are generally applicable to all formsof roofs. These methods vary and involveincorporating flexible or rigid insulating materialin or under the roof cladding or structure, or theuse of self-supporting insulating materials,which are strong enough to act as substructureto the covering. Due to the large selection ofinsulants available, manufacturers should alwaysbe consulted to ensure that the keyperformance requirements are met.

Eaves

Fascia and soffits must be constructed toachieve the same lifetime as the roof coveringand require little or no maintenance.

Overhanging eaves can be useful in solarshading and reduce overheating. However, theposition of gutters must be designed so thatthe eaves do not obstruct maintenance accessor cause any health and safety issues formaintenance operatives accessing the gutters.

Low level eaves/roofs must be considered withregard to arson and security, as they arepotentially vulnerable to being set alightexternally.

In cold roof constructions, the eaves must havea proprietary continuous ventilator inaccordance with Building Regulations.

If discontinuously supported roof coverings arefixed to the fascia to alleviate wind uplift, themanufacturer of the roof covering must beconsulted to ensure that the fascia system iscompatible.

Rooflights

Rooflights are discussed in the ‘Daylight’ sectionon page 28 as an effective way to introducelight into the building. Rooflights may bepolycarbonate, glass or other plastic translucentsheeting. They should all comply with theacoustic, thermal, fire and safety requirementscontained within this document.


Roof constructionRoofs may be pitched or flat, with the definitionof a pitched roof being one that exceeds 10degrees. The definition of a flat roof is one thatis greater than 1:80 (the minimum finished fallallowable under BS 6229) but less than 10degrees. The choice between flat or pitchedroof is generally an aesthetic one dependant onthe designers’ choice of roof form and roofcovering. In general, continuously supportedroof coverings are flat and discontinuouslysupported roof coverings are pitched. Commonto all roofs is the roof build up, which may bewarm, cold or inverted construction, asdescribed below.

The chosen roof system must satisfy allacoustic, thermal, fire, durability and safetyrequirements covered in this section of thedocument.

Warm roof construction – continuouslysupported roof coverings

The insulation material is placed between thewaterproof covering and the roof deck, with avapour control layer on the warm side of theinsulation. This form of roof construction maybe considered for school buildings because thedesign should ensure that the deck ismaintained at a temperature above that whichcould cause condensation at this level duringservice. A warm roof construction also offers anincreased usable volume, without anycorresponding increase in overall building size.Warm roofs can also incorporate a top layer ofpaving, ballast or green roof (as described ingreen roofs section on page 20) above thewaterproof membrane if a protective/drainagelayer is incorporated.

The following should be noted:

• Allow for thermal movement of insulationmaterials that are not dimensionally stable.This may involve the inclusion of expansionjoints within the insulation layer atappropriate intervals.

• Avoid wetting the insulation during theconstruction phase, particularly when it isused within systems where it is enclosedbetween impermeable layers of vapourcontrol layer and roof covering/underlay.

• Where frequent roof traffic (other than routinemaintenance) is anticipated, the covering andinsulation manufacturers should be consultedfor advice on the provision of appropriatewalkway design requirements.

• Roof loads will be transferred to the structurevia the thermal insulation, so the appropriatechoice of compressive strength is important.


Warm roof construction – discontinuouslysupported roof coverings

The insulation material is placed immediatelybelow the roof covering, with a vapour barrieron the warm side of the insulation. This form ofroof construction may be considered for schoolbuildings because of the reduced risk ofcondensation and more stable temperaturesprovided in comparison with cold roof solution.However, the following should be noted:

• Avoid wetting the insulation during theconstruction phase, particularly when it isused within systems where it is enclosedbetween impermeable layers of vapourcontrol layer and roof covering/underlay.

• Where frequent roof traffic (other than routinemaintenance) is anticipated, the covering andinsulation manufacturers should be consultedfor advice on the provision of appropriatewalkway design requirements.

• A warm roof also has an increased usablevolume, without any increase in overallbuilding size.

Cold roof construction – continuouslysupported roof coverings

The insulating material is placed immediatelyabove the ceiling within the roof deck zone. Theroof deck and roof space are at or near theexternal air temperature. Roofs of this typerequire the void below the roof deck/coveringto be well ventilated if condensation problemsare to be avoided.

This form of roof construction forcontinuously supported roof coverings is notrecommended for school buildings for thefollowing reasons:

• The structural support will typically form acold bridge between the high and lowtemperature zones of the roof construction.

• The mandatory requirement for external aircirculation in practice is difficult to achieve,particularly where there are abuttingelevations or changes in building geometry,thereby increasing the risk of condensationaccumulation within the system.

• The roof deck and roof space are at or near tothe external air temperature for much of theyear, which is substantially below that inside thebuilding. There is therefore considerable dangerof warm humid air from inside the buildingpenetrating and condensing within the coldroof space. This is a particular danger in schoolsas they tend to be humid environments.

• The ceiling will become the air barrier andvapour control layer, so it is difficult to achievethe pressure test requirements of BuildingRegulations Part L2 when access hatches andmechanical and electrical items areintroduced into the ceiling.

• Post-construction modifications to cold roofsare difficult to achieve because they involvecomplex details and additional componentsto improve ventilation.

• Future upgrading to improve energyefficiency is difficult and can increasecondensation risk.

Additionally, any form of mixed cold andinverted roof construction is not acceptablefor continuously supported roof coverings.

Cold roof construction – discontinuouslysupported roof coverings

The insulating material is placed immediatelyabove the ceiling. The roof deck and roof spaceare at or near the external air temperature.Roofs of this type require the void below theroof deck/covering to be well ventilated ifcondensation problems are to be avoided. The advantages of this type of roof constructionare as follows:

• The heated volume and the quantity ofinsulation material needed are minimised.

• Very high levels of insulation can be achievedbecause there is virtually no restriction on thethickness of insulation that can be installed.

This form of roof construction may beconsidered for school buildings. However, thefollowing should be noted:

• The external roof covering and roof space areat or near the external air temperature.

• Roofs of this type require that adequatemeasures are taken to avoid the risk ofcondensation occurring on the surfaces belowthe roof covering. This should be either byproviding adequate ventilation to the void; orby using a roofing underlay with lowresistance to water vapour that has TechnicalApproval from an UKAS (United KingdomAccreditation Service)-accredited technicalapproval bodies for use in this application. The use of a suitable, continuous vapourcontrol layer on the warm side of theinsulation or well sealed ceiling to BS 5250 isalso required.

• The ceiling will become the air barrier andvapour control layer, so it is difficult to achievethe pressure test requirements of BuildingRegulations Part L2 when access hatches andmechanical and electrical items areintroduced into the ceiling.



Inverted roof – continuously supported roof coverings

The insulation is placed above the waterproofroof covering and provided with some form ofballast on top, such as paving slabs, gravel orgreen roof (as described in the green roofingsection on page 20). This form of construction issimilar to a warm deck but has the additionalfeature of the insulation and ballast protectingthe roof membrane from thermal movementand foot traffic. This form of roof constructionmay be considered for school buildings. The following should be noted:

• The structural deck must be of sufficientthermal mass to avoid surface condensationon its soffit when the waterproof covering iscooled rapidly during heavy rain or snow melt.

• Sufficient insulation must be provided toensure that the underside of the waterproofcovering is warm enough at all times toprevent condensation of any water vapourpassing into the roof space.

• The insulation material must be unaffected bywater and capable of withstanding normalroof loads.

• The roof covering will be hidden below theinsulation and ballast, so its waterproofintegrity must be ensured before covering itup, as leaks will be difficult to locate after theinsulation and ballast have been put in place.

• Rainwater will affect the insulation’s U-value,so when calculating U-values a correctionfactor should be used as set out in BS EN ISO6946 (see ‘References’, page 48), ignoring theeffect of ballast etc. and, in the case of a‘green’ roof, ignoring the effect of soil,vegetation etc.

• A drainage mat is required if the deck is fullysealed.

• For a given U-value, the inverted roof has thegreatest roof zone depth of any roof type, sothe design must make provision in terms ofupstand heights, parapets, verges etc.

• The designer must be satisfied that the ballastchosen is adequate to resist the design winduplift. Methods of ballasting are dealt with inBRE digest 295 and 311.

Inverted roofs are not suitable fordiscontinuously supported roof coverings.


Roof pitch

The following generic recommendations are made for roof pitches in normal situations. Where abnormal conditions are present, such as in elevated sites, near to the coast, areas of heavy snow fall or severe exposure, the roof covering manufacturer must be consulted. In all cases, the roof covering manufacturer should be contacted to determine whether they have any additional requirements.

Minimum roof pitch

1:40 Continuouslysupported roofcoverings

Notes

This is the design fall, as defined in BS6229, to achieve a minimum site finishedfall of 1:80 at all points (to account for sitetolerances).

Profiled sheeting/insulated panels:

1.5 degrees (roof with no end laps andwelded openings)

4 degrees (roofing sheeting withopenings, end laps etc.)

Natural Slates:

The minimum pitch for natural slates is 20degrees, but depends on slate size andexposure.

Interlocking single lap concrete and clay tiles:

The minimum pitch for clay and concreteinterlocking tiles is dependent on thedesign of the tile; the manufacturer shouldalways be consulted. Some designs maybe laid at 12.5 degrees.

Double lapped concrete and clay plaintiles:

The minimum pitch for clay and concreteplain tiles is 35 degrees. For clay tiles notmeeting the dimensional and geometricrequirements of BS EN 1304, e.g.handmade tiles, the minimum pitch is 40degrees.

Discontinuouslysupported roofcoverings

Profiled sheeting/insulated panels:

Always consult roof coveringmanufacturer. Some products requiregreater falls.

Rafter pitch and length should be asrecommended by manufacturer.

Natural Slates:

The minimum pitches are recommendedfor normal conditions – they apply torafter lengths not more than 9 m in drivingrain, exposures of less than 56 l/m2 perspell and 6 m in driving rain exposures of56 l/m2 per spell or greater.

Single lap:

Where longer rafter lengths (more than 10m) or more severe conditions areexpected, the manufacturer should beconsulted on the suitability of the productand appropriate precautions to be taken,which may include choosing a suitabledesign of tile, increasing headlaps,installing under-tile secret gutters, etc.

Double lapped:

The presence of certain roof features suchas eyebrow dormers may increase thedesign fall required.


Building tolerances

It is advisable to note the importance of thebuilding tolerances on the roof covering.Generally, it is the job of the roof to allow forthe accumulation of design tolerances withinexternal walls, as these will be most prevalent atthe eaves.

It should be noted that a concrete frame couldbe +/- 30mm from plumb and still be within itsacceptable tolerance zone, which could create30mm dips in a zero fall concrete roof deck. It isimperative that no matter what structure orsupport is provided below the roof covering,the following are achieved:

• The eaves detail must allow for a degree ofsite tolerance and manufacturers’recommendations must be followed for thesystem being installed.

• The roof covering must achieve the minimumpitches stated in the ‘Roof pitch’ section onpage 15, regardless of the tolerances withinthe roof deck. This will ensure that BuildingRegulations Part H is complied with, whichstates that: ’adequate provision shall be madefor rainwater to be carried from the roof of thebuilding.’

In the case of metal cladding roof systems,excessive tolerances in the purlins duringerection or under the action of constructionloads can affect the performance of thecladding system. Guidance on the selection andinstallation of purlins is given in Best practice forthe specification and installation of metal claddingand secondary steelwork (SCI publication p346 –2006).

Roof terraces

Roof spaces can be used for additional outdooraccommodation, incorporating the inverted orwarm roof constructions described in roofconstruction section on page 11. Whendesigning roof terraces/green roofs, particularattention needs to be given to door thresholds,especially when the threshold is level fordisabled access. Drainage channels are requiredand attention must be given tooverhangs/canopies. The roof coveringmanufacturer should also be consulted. It isessential that parapet heights and guard railingare designed in accordance with BuildingRegulations and that all details are fullydiscussed with the roof covering manufacturerto ensure the roof remains fully water tight.

Roof terraces/green roofs should be part of theoriginal design and not introduced as an afterthought when the school is in operation.

Care must be taken that the damp proof courseis not bridged and that a minimum of 300mm ismaintained between roof covering and theadjacent wall’s damp proof course.



Drainage

The disposal of rainwater from roofs requirescareful consideration. Part H of the BuildingRegulations states that: ‘adequate provisionshall be made for rainwater to be carried fromthe roof of the building’. Defects in design orconstruction can be costly and difficult torectify; and maintenance is often neglecteduntil there are serious leaks or floods. Largeroofs in particular require well judgedcalculation, careful detailing and supervision,plus accurate coordination on site of severaltrades, such as structural steel, roofingmembrane and plumbing.

Roof drainage, including gutter outlet and pipedimensions, must be calculated by the specialistrainwater goods manufacturer using guidancein BS EN 12056 and BS 6367.

The design objectives should be:

• A simple layout, avoiding indirect routes torainwater outlets.

• On flat roofs, avoidance of box gutters withinthe roof area.

• The shortest possible distances to rainwateroutlets; an additional rainwater outlet may pay

for itself in reduced roof zone depth.

• Fully accessible rainwater outlets formaintenance and replacement.

• Anti-back up design, with sealed junctionsbetween gulley and down pipe.

Drainage design generally should ideally beginearly in the design process as it will affect:

• Below ground drainage (internal layout, e.g.pipe routes, boxings and the integrity of fire-resisting constructions).

• External appearance (gutter and down-pipesize, location and relationship to doors andwindows.

Rainwater down pipe design should beconsidered for ease of maintenance,susceptibility to vandalism and prevention ofclimbing. There are a number of advantagesand disadvantages with both internal andexternal rainwater pipes:

• Internal rainwater pipes are less susceptible toabuse. However, they need to be accessible,maintainable and may require acoustictreatment. (Siphonic systems will not requireaccess points, as they are sealed systems.) Also,if a leak occurs it will be within the building.

• External rainwater pipes keep the wateroutside the building and are accessible formaintenance. The disadvantage is that theyare exposed and therefore open to abuse. Thiscan be reduced by good design, for exampleusing square pipes flush to the wall.

Bends in down pipes and horizontal runsshould be minimised and all horizontal runs laidto fall. All down pipes must have rodding eyesat floor level, positioned so that a blockagebetween down pipe and the surface waterdrainage system can be cleared by rodding.



All gutters must be laid to fall and providedwith overflow pipes to discharge in an obviousplace to provide early warning of blockedrainwater outlets. Mechanically fixed leaf guardsmust be provided to all outlets and will also actas a guard against balls and foreign objectsblocking the outlets. Any part of the roof mustnot rely on one outlet alone.

Additional requirements for tiled and slatedpitched roofs:

• Sheeting used for inclined valleys, horizontalgutters, flashings, soakers and saddles shouldconform to BS 5534 Part 1, Table 3 and bedeveloped in accordance with roof coveringmanufacturers’ recommendations.

• The minimum valley gutter widths are statedin BS 5534 Part 1, Table 14 and should bedeveloped in accordance with roof coveringmanufacturers’ recommendations.

Movement

All roofs comprise a number of elements thatexpand and contract or move in relation toeach other, subjecting the waterproofingelement to stress. Building movement jointsmust be taken through the roofing system anddetailed in accordance with the manufacturers’details to achieve the required structuralmovement. Manufacturers’ advice should alsobe sought for any movement joints requiredwithin the deck, insulation or covering.

Particular care must be taken over flat roofs andbonding of any materials to the roof deck. Astructural engineer will need to calculate theamount of movement expected in the roofstructure in all three planes (up, down andsideways). With all systems, wind load should beconsidered and manufacturers’ advice obtainedfor fixing all elements, based on the designwind load in accordance with BS 6399-2.

Compatibility of components

Compatibility between the various materialelements of a roofing system is vital to thelongevity of the system.

This rule applies both to the components in theroof and also to any elements interfacing withthe waterproofing system, such as verticalcladding or rendering.

The selection of components within the roofingsystem should be discussed in detail with themanufacturer of the roof covering to ensurecomplete compatibility between components.Incorrect specification of incompatiblecomponents will lead to premature failure ofthe roofing system.

Lightning protection

The installation of a well-designed lightningprotection system on a structure should be inaccordance with BS 6651:1991, Code of practicefor protection of structures against lightning. Thisrequires effective integration of the roofing andelectrical design at an early design stage, sincelightning protection works are usually part ofthe electrical contract package. This mayinclude fixing tapes from steel liner sheets tothe steel frame or the inclusion of tapes/rodsinto foundations, which need to be consideredat the beginning of the design phase.

The roof covering manufacturer must always beconsulted to ensure compatibility with thelightning protection system. There must be nopenetrative fixings through flat roofs, becauseof the risk of water ingress.


Off-site/on-site fabrication

Alongside traditional forms of on-siteconstruction process, off-site fabrication canhave numerous benefits, such as reducedprogramme times, improved quality control,lower costs, lower site waste and increasedproductivity. However, it is for the design andconstruction team to consider the mosteffective approach for their particularlocation/design. All the key performancerequirements apply to both on-site and off-siteconstruction. Particular care should be taken toensure that sufficient allowance has been madefor site tolerances to be overcome whenproducing components off-site.

Plant

All penetrations through the roof and roof levelplant must be co-ordinated at an early stage inthe design and must be provided in adedicated zone to minimise roof penetrationsand access required to the roof.

Where plant is required on the roof, thefollowing must be considered:

Generally:

• Service penetrations must be provided withupstands, apron flashings or weatheringcowls, all in accordance with the roof coveringmanufacturer’s details.

• Electrical connections should be installedfollowing manufacturers’ recommendations toensure a weather-tight seal.

• The roof substructure must be able to supportthe dead loads produced by the plant.

• Where kitchen extracts are provided, roofcovering manufacturers should be consultedto ensure that the exhaust gases will notaffect the roof covering.

• See CDM recommendations in health andsafety section on page 34.

• Acoustic issues affecting any rooms belowshould be addressed, including vibrationnoise through the structure.

Additionally for continuously supported roofcoverings:

• Upstands or additional structure must beprovided to ensure that the plant is locatedadequately above the roof finish. This willenable inspection of the cover and futuremaintenance/replacement of the roof covering.

• Support structures that penetrate the roofcovering must be designed to avoid coldbridges and maintain the waterproofcovering. Any differential movement betweenthem and the roof system must beestablished at the design stage.

• The roof covering must be protected fromfoot traffic and maintenance equipment bydedicated walkways.



Additionally for discontinuously supported roofs:

• Appropriate measures must be taken toensure that the penetrations through the roofcovering to secure the plant to thesubstructure are designed to be weatherproof. Typically, manufacturers supplyappropriate flashings for this task. In any case,the manufacturers’ recommendations mustalways be followed.

• The plant itself must be adequately designedand mechanically fixed so as to resist the windloads and snow loads prescribed for UKconditions in BS 6399, Loading for buildings,Parts 2 and 3.

Green roofs

Design

The type, size and design of each layer of agreen roof will depend on the proposedlandscape. As can be seen from the attachedgreen roof pictures, there is a range of possibleextensive and biodiversity type landscapes, eachrequiring a different support system beneath it.

A successful green roof system must basicallyreplicate nature but within a very compressedbuild up. Whether it is a biodiversity (brownroof), extensive or intensive landscape, the buildup should always consist of:

• A high quality waterproofing system,incorporating a root barrier to German FLLstandards or equivalent.

• Moisture retention/protection layer.

• Drainage layer.

• Filter layer.

• Manufactured/recycled growing medium.

• Appropriate components – outlet inspectionchambers, linear drains etc.

It is important that the client and designer clarifythe performance they require from their greenroof. For example, is it in response to storm watermitigation, biodiversity, or planning constraint?

The final design will be controlled by a numberof fundamental factors:

• Climate dependant factors, such as rainfall,topography, periods of drought and frost.

• Structural dependant factors, such as loadings,building height, wind tunnels betweenbuildings, roof slope.

• Plant dependant factors, such as in shade, orfull sun, north, south, east or west facing,prevailing wind.



The roof covering will be hidden below theinsulation and ballast/growing medium, so itswaterproof integrity must be ensured beforecovering it up, as leaks will be difficult to locateafter the insulation and ballast have been put inplace.

For further detailed guidance on green roofs,see CIRIA publication C644 – Building greener –Guidance on the use of green roofs, green wallsand complementary features on buildings.

Maintenance

Every type of green roof system will also requiremaintenance in some form or another, initiallyfor a period following the installation of theplants, and subsequently for ongoingmaintenance to keep the green roof flourishing.

The specifier should put into the tenderdocuments that the contractor must price inthe cost of post installation maintenance for aperiod of at least 12 months. This should ensurethat a healthy green roof is handed over.Following this period, the responsibility forongoing maintenance is the client’s.

Maintenance and irrigation of green roofs mustbe considered, otherwise there is an inherentfire risk, as discussed in the fire section on page25. The designer must also provide safe accessfor maintenance, as discussed in the health andsafety section on page 34.

Benefits

A green roof offers excellent environmentalbenefits to the specifier’s client:

• Storm water retention – helps to reduceground drainage capacity requirements.

• Provides both thermal and sound insulation.

• Replaces landscape lost under the foot printof the building.

• Cools and humidifies the surrounding area –attracting wildlife and absorbing dust andtraffic fumes.

• When manufactured from recycled products,the green roof components are an excellentoutlet for old materials.

• Absorbs carbon dioxide and produces oxygen.

Thermal performanceThe principal properties to be considered areoutlined below. These will also be required byBuilding Control when they are checking abuilding’s thermal design.

Design standards

Approved Document L2A of the BuildingRegulations 2000 (2006 edition) details theapproach for compliance with energy efficiencyrequirements in respect of ‘New buildings otherthan dwellings’. Minimum compliance isdemonstrated by meeting the five criteria setout below:

• The Building Emission Rate (BER) as calculatedusing an approved tool must not exceed theTarget Emission Rate (TER) by reference to anotional building. The approved calculationtools comprise the Simplified Building EnergyModel (SBEM) or approved commercialsoftware.


• The performance of the building fabric andfixed services must be no worse than setdesign limits:

– The area weighted U-value for all the roofelements must be no more than 0.25W/m2K. This is the performance U value foruse in the notional building calculationrequirement of L2A (2006 edition). No oneelement within the roof constructionshould be greater than 0.35W/m2K.

– The area weighted U-value for all therooflights must be no more than 2.2 W/m2K.This is the performance U value for use inthe notional building calculationrequirement of L2A (2006 edition).

• Those parts of the building that are notprovided with comfort cooling systems musthave appropriate passive control measures tolimit the effect of solar overheating.

• The performance of the built building mustbe consistent with the BER.

• Necessary provisions for energy efficientoperation of the building must be put inplace.

The technical provisions of L2A (2006 edition)require significantly higher performancestandards in comparison with previous 2002levels. For school buildings that are naturallyventilated and heated, the minimumimprovement required in terms of the reductionof the annual CO2 rate is around 23%.

Experience has shown that, to achieve theminimum improvement levels for schoolbuildings as determined by L2A (2006 edition),a combined improvement in fabric, heating,ventilation, lighting and air conditioning (whereapplicable) performance standards are required.For design U-values for roofs to reasonably

contribute towards the 23% improvement, it isconsidered good practice to exceed the limitinginsulation standards denoted by Table 4 ofApproved Document L2A.

The Building Research EstablishmentEnvironmental Assessment Method for Schools(BREEAM) 2006 encourages buildings that aredesigned to minimise the CO2 emissionsassociated with their operational energyconsumption. Under BREEAM Schools 2006,‘Energy, Reduction of CO2 emissions’, credits areachieved based on the percentageimprovement in the assessed design’s predictedBuilding CO2 Emissions Rate (BER) over theTarget CO2 Emissions Rate (TER). The number ofcredits achievable range from one to 15 forimprovements of from 1% to 70% above theminimum requirements of L2A (2006 edition).

Due consideration should also be given to anyfuture thermal upgrades that may be requiredwhen designing the perimeter. Particularconsideration should be given to upstands,cavity trays, damp proof courses, and door andwindow thresholds, which should be higherthan the minimum 150mm above the finishedsurface level, to allow for further insulationupgrades to the roof over the 60 year lifetime ofthe building. The minimum recommendation is300mm. However, future thermal requirementscannot be predicted.


Building fabric

Air permeability

Buildings should be reasonably airtight to avoidunnecessary space heating and coolingdemand. The design of the air permeability ofthe envelope (which includes the total area ofthe perimeter walls, roofs and ground floorarea) should be no worse than 10m3/(h.m2) atan applied pressure of 50 Pascals. Betterstandards of air permeability are technicallydesirable in buildings with mechanicalventilation and air conditioning.

Once the external envelope has beencompleted, the building must be tested by anapproved air pressure testing company to showcompliance with the Building Regulations.

Guidance on appropriate design detail andconstruction techniques to achieve thiscompliance is provided by:

• Minimising cold bridging and air tightness:Accredited Construction Details (ACDs).

• BS 9250: Code of practice for control ofairtightness in pitched roofs.

For metal cladding roof systems, guidance onappropriate design detail and constructiontechniques to achieve this compliance isprovided by:

• MRCMA/EPIC Technical Paper 17 (2007) –Design guide for metal roofing and cladding tocomply with energy requirements of UK BuildingRegulations, 2006.

• BRE IP 1/06 – Assessing the effects of thermalbridging at junctions and around openings inthe external elements of buildings, BRE, 2006.

• EPIC – Insulated panels for external roof andwall cladding – Guidance on compliance withthe conservation of fuel and power BuildingRegulations’ 2006.

Thermal bridging

The building fabric should be constructed sothat there are no reasonably avoidable thermalbridges or gaps in the insulation layers withinany elements, at the joints between elements orat the edges of elements such as those aroundroof lights and glazing. For continuouslysupported warm roof systems attached via amechanical fastener system, the use of tubewashers is recommended to reduce theincidence of thermal bridging.

For traditional flat and pitched roof systems, L2A(2006 edition) refers to Minimising cold bridgingand air tightness: Accredited Construction Details(ACDs) on the planning portal:www.planningportal.gov.uk/england/professionals/en/1115314255826.html.

For metal cladding roofing systems, L2A (2006edition) refers to MRCMA/EPIC Technical PaperTP17, which details how thermal bridges shouldbe assessed. Further guidance can also befound in BRE IP 1/06 – Assessing the effects ofthermal bridging at junctions and aroundopenings in the external elements of buildings,BRE, 2006.

AcousticsThe external roof represents a significantportion of the building’s surface area, so itsacoustic performance plays a significant role inestablishing an acceptable environment withinthe rooms below. Good acoustic standards inteaching areas are crucial for the learningprocess, because if pupils cannot hear properlytheir ability to learn is likely to be adverselyaffected.


Planning and layout

The control of noise pollution must beaddressed from the earliest stage in the designprocess. For example, when schools buildingsare to be located adjacent to busy roads, theywill require the use of intelligent design –planning and layout. It is possible to identifynoise-sensitive areas and to separate them fromnoisy areas using buffer zones, zoning, noisescreening or by locating buildings a suitabledistance apart. When considering externalnoise, such as from roads or aircraft, specialmeasures are required and it may be necessaryto consult an acoustic expert on the location ofnoise sensitive rooms such as classrooms andexamination spaces. In all cases, an acousticexpert will be required to calculate the existingexternal noise levels so that compliance withBuilding Bulletin 93, Indoor ambient noise levelscan be checked.

Indoor ambient noise levels

Once the planning and layout strategy havebeen optimised, the acoustic performancerequirements of the roof construction should beconsidered. The acoustic performance of anexternal roof is heavily dependent on theselection of materials (especially the mass of theceiling and roof layers, including the presenceof sound absorbing material).

Consideration should also be given to theacoustic performance of other components,such as rooflights, the external wall constructionand external windows and doors, which mayinfluence internal noise levels.

A calculation of the internal noise levelaccording to BS EN 12354-3:2000 can be used inorder to estimate and confirm that a proposedconstruction will achieve the levels required byTable 1.1 (Performance standards for indoorambient noise levels – upper limits for theindoor ambient noise level) of Building Bulletin93. The objective is to provide suitable ambientnoise levels for speech within study activities.Indoor ambient noise levels include noisecontributions from:

• External sources outside the school premises(e.g. road, rail, air traffic).

• Building services.

• Rain noise.

Impact noise from rain on the roof cansignificantly increase the indoor noise level andmust be considered at an early point in the roofdesign. It is essential that provision be made inthe design of lightweight roofs and rooflights sothat the noise from rain affecting internalspaces does not result in undue disturbance. Toensure that the appropriate provision is madefor impact noise from rain as part of the roofdesign, it is required that the increase in criteriafor noise intrusion from external sources during‘heavy’ rainfall does not exceed the levelsdefined in Table 1.1 by more than 20dB in thedesign calculations. A credit will be awarded formeeting this requirement under BREEAMSchools 2006. See Health and wellbeing, Acousticperformance, HW17, p49.


An acoustic expert will be required to calculatethe existing external noise levels and assess thatthe proposed roof construction will achieve therequired ambient noise levels within the roomsbelow.

Wherever the required ambient noise levelscannot be achieved by the roof constructionproviding adequate sound insulation, it istypical to treat the ceiling. Where the ceiling isalso the soffit of the roof, additional lining andsound absorption materials may be required.The solution may involve the use of an acousticsuspended ceiling or a perforated metal liningtray solution, and is specific to the room designand usage type as required by Table 1.1 ofBuilding Bulletin 93. This should be developedwith an acoustic expert.

Where internal walls abut roof soffits, flankingsound transmission must be considered and thepartition sealed to the roof soffit in accordancewith the partition manufacturer’srecommendations, so that the partition’sacoustic properties are maintained and therequired movement in the roof deck achieved.Where the roof soffit is profiled, an acousticexpert should provide details to maintain theacoustic integrity between rooms.

Performance in fireCompliance with the Building RegulationsApproved Document B (ADB) and BuildingBulletin 100 will help ensure that a requiredminimum standard of life safety will beachieved in the event of a fire. ADB requires thebuilding to be designed and constructed sothat there are appropriate provisions forwarning and escape for building occupants. Itprovides guidance for the fire performancerequirement of roofs when the fire source is

either external or internal to the roofconstruction. For schools, the following shouldbe adhered to:

• Internal surfaces: The ‘surface spread of flame’requirements to be Class 1 to BS 476 Part 7 orEuropean standard classification C-s3, d2.

• ‘External surfaces: fire resistance’ requirements– The requirement is for the fire roof exposurerating to be AA, AB or AC to BS 476 Part 3, orEuropean standard classification BROOF(T4) toENV 1187 Part 4, as defined in EN 13501-5.

The external fire performance is expressed as arequirement for the whole roof construction,including deck and covering, characterised bypenetration of fire and spread of flame.

The first letter of the designation refers to thetime to penetration (A = those specimens thathave not been penetrated in one hour) and thesecond letter is a measure of the spread of flame(A = those specimens on which there is nospread of flame, B = those specimens on whichspread of flame is less than or equal to 533mm, C= those specimens on which spread of flame isgreater than 533m).

ADB also requires 30 minutes’ fire resistance asregards load bearing capacity, integrity andinsulation to the underside of the roof in thefollowing locations (refer to BS 476: Part 22 orEuropean standard EN 13501-2):

• When the roof and its support structure arepart of an escape route, including anyopening within 3m of the escape route.

• When the roof performs the function of afloor.


Due consideration should also be given to thefollowing additional guidance:

• Junction of compartment wall with roofdetails: a 3 metre wide zone centred over thecompartment wall with a covering ofdesignation AA, AB or AC on a substrate ordeck of a material of ‘limited combustibility’ isrequired (B3, diagram 30(a)).

• Sprinkler systems.

• Fire rated ceilings.

• Fire stops within the building.

• Insertions of cavity barriers within the roofvoid where appropriate.

• Insulation in accordance with BuildingRegulations Approved Document B (ADB) andany insurance requirements.

Combustible thermoplastic insulation materialshould not be carried over the compartmentwall, as a core to double-skinned roof sheetingor otherwise (paragraph 8.29 to 8.31 anddiagrams 3a and 3b of Approved Document B,2006). Its use within the roof construction orelsewhere within the building could alsoinfluence insurance terms (see ‘Performance infire’ section, page 25, ‘Insurance requirements’) ,though other insulated panel and claddingsystems that have LPCB certification areaccepted.

ADB Table A6 defines non-combustiblematerials as any that are classified as A1 inaccordance with BS EN 13501-1:2002. Similarly,ADB Table A7 defines materials of limitedcombustibility as either any material listed inTable A6 (non combustible) or any materialclassified as Class A2-s3, d2 or better inaccordance with BS EN 13501-1:2007.

Where the roof forms the soffit of the internalroom, the internal lining must be Class 1 (Euro-equiv C-s3, d2) surface spread of flame to BS476 Part 7 and Class O (Euro-equiv B-s3, d2) inmeans of escape.

Designers should also refer to Building Bulletin100 Design for fire safety in schools, in particular,preventing arson by stopping access fromsurrounding buildings or walls to roofs, asdefined in Building Bulletin 100, Section 8.8.

Rooflights’ minimum ‘surface spread of flame’requirements must be Class 1 to BS 476 Part 7or European standard classification C-s3, d2. Thelower surface must be classed TP(a) rigid. Norooflight must be placed closer than 6 m to therelevant boundary, unless it has a AA, AB or ACfire rating. Thermoplastic rooflights are notsuitable for use in the zone of the roof 1500mmwide on either side of a compartment wall (ADBSection 14: Roof coverings, Diagram 47, Note 3).

Unless green roofs (as described in green roofsection on page 20) are maintained andirrigated, they are likely to consist mainly ofgrasses and weeds, which often dry out in thesummer months when schools are at theirgreatest risk of fire. The designer should alsoincorporate gravel margins around openings, infront of walls or other structures that rise fromthe roof, and around the edges of the roof toact as fire breaks.

Insurance requirements

The building insurers should always beconsulted about fire performance to establishwhether they have any requirements additionalto Building Regulations.


For guidance, the basic principles necessary toachieve adequate levels of property andbusiness protection are defined in the LPCB RedBook and the Design guide for the fire protectionof buildings – Essential principles sponsored byInFiRes, the Insurers’ Fire Research StrategyFunding Scheme, under the projectmanagement of the Fire Protection Association.This is one of a number of documents thatmake up the FPA Design guide for the fireprotection of buildings, a development from theLPC Design guide for the fire protection ofbuildings, 2000.

The 12 basic principles in the above documents,whilst not mandatory, encourage consultationwith insurers at the earliest stage of design,thereby ultimately influencing the insuranceterms. One of the overriding themes is thepreferred use of non-combustible materials andlimitations to combustible insulation products.Principle 2 states that ‘with the exception ofjoinery products, the building shall beconstructed from materials/products that willnot make a significant contribution to the earlystages of a fire or contribute to the spread offire’. Specifically, reference is made to Euro ClassA1 or A2 products (insurers may ask for aspecification higher than s3, d2) and, wherebuilt up cladding or sandwich panel systems areused, LPCB (Loss Prevention Certification Board)approval to the requirements of the appropriatepart and grade of LPS 1181: Part 1: Issue 1.1Series of fire growth tests for LPCB, Approval andlisting of construction product systems, Part 1:Requirements and tests for built-up cladding andsandwich panel systems for use as the externalenvelope of buildings. See 2.2 of the LPC Designguide for the fire protection of buildings.

Principle 6 of the FPA Design Guide requiresthat installation of certain materials should becarried out under the UKAS-approved thirdparty accreditation scheme.

Regulatory reform (fire safety) order

Following changes to fire safety legislationintroduced through the Regulatory Reform FireOrder in October 2006, designers are nowrequired to communicate all aspects of thedesign that may affect the eventual fire riskassessment, including the use of combustibleproducts used in the construction. Thisunderlines the new fire prevention approach,which asks designers/specifiers to identify andaddress potential fire risks. In order toaccomplish this effectively, specifiers mustensure that they have sufficient informationrelating to their proposed construction. The consequences of errors resulting fromjudgements based on the acceptance ofmisleading or inaccurate information could lead to criminal prosecution.

For guidance on all aspects of fire safety ineducational premises, refer to the HMSO’s Fire Safety Risk Assessment in EducationalPremises, 2006.

Environmental

Sustainable construction

Environmental impact ranges from consumptionof natural resources and energy duringmanufacture and installation, through to removal,recycling and disposal. Realistic durability andmaintenance input estimates are an essentialrequisite of impact studies. These parametersfeed directly into BREEAM requirements.


BREEAM Schools is the standard tool forassessing the environmental impact of a school.Within the BREEAM Schools assessment,construction elements used within theproposed roof system are rated usinginformation from the BRE Green guide tospecification. The ratings for components are A*to E, with A* being the most environmentallyfriendly. It is encouraged that the specifierchooses the most sustainable productsavailable that meet the performance criteria. A product’s environmental rating should alwaysbe checked with the manufacturer.

It is also necessary to comply with theGovernment’s timber procurement policy,found at: www.proforest.net/cpet/uk-goverment-timber-procurement-policy/timber-guidance

For guidance on the percentage of recycledcontent in a new build and opportunities toincrease the overall use of recycled material inthe building, refer to the RC toolkit provided bythe Waste and Resources Action Programming(WRAP) group. This can be found at:www.wrap.org.uk

Daylight

Rooflights have been recognised as an efficientdevice for introducing daylight into buildings.Modern rooflights when combined with amodern lighting system incorporating daylightsensors are effective in cutting a building’senergy consumption by reducing the need forlighting during daylight hours, helping toreduce the building’s carbon footprint.

Guidance on rooflight design and compliancewith Part L of the Building Regulations is givenin the second tier document referenced fromPart L Building Regulations: ‘Designing withrooflights: Supporting the guidance in AD L2A &AD L2B (2006)’ (issued by the NationalAssociation of Rooflight Manufacturers) whichshows that optimum reduction of carbonemissions will be achieved with rooflight areaup to 15-20% floor area.

In addition BS 8206 part 2 provides informationon recommended daylight factors in areas suchas atriums.

The average U-value of the rooflights used mustbe a minimum of 2.2 W/m²K (when assessed inthe vertical plane) in order to comply with PartL Building Regulations.

Care should also be taken when specifyingrooflights that the following are considered anddiscussed with the manufacturer:

• Light transmission levels.

• The effect of increased rooflight area inreducing carbon emissions as calculated by anapproved calculation tool, as required by PartL2 of Building Regulations.


• Solar overheating – the maximum internalgain allowed in Building Regulations Part L2 is35 W/m² from all elements, including lighting,occupants, internal processes and solar gain.See NARM guidance and CIBSE guide TM37 –‘Design for improved solar shading control forguidance on solar overheating’. Externallymounted shading devices are more effectivethan tinted window film as they control boththe heat gain and solar glare.

• Non-fragility rating as stated in health andsafety section on page 34 of this specification.

• UV degradation.

• Compatibility with the proposed roofcovering system.

• Loads caused by snow, ice, standing waterand self weight. Guidance on loadings isavailable in BS 5516 and BS 6399 part 2 and 3.

• Deflection caused by wind loads.

• The performance in fire shall conform to therequirements of Building Regulations as statedon page 26.

• Where upstands are required to ensure thatthe rooflight is above the plane of the finishedroof, it shall be suitably insulated.

• An Acoustic Expert should check that theproposed rooflight construction will achievethe required indoor ambient noise levels andintrusion of rain noise as stated in the acousticsection of this report.

• Within atria consideration shall be given tousing the rooflights for ventilation and smokecontrol as required under BS 5588 part 7.

• Consideration shall be given to effectivedrainage of rainwater and condensation fromthe rooflight. If water is allowed to collect onsurfaces close to horizontal, problems withsediment build up and long term etching maybecome apparent.

The most commonly used glazing materials forrooflights are glass (for skylights and panelglazing systems) and polycarbonate (for domes,continuous barrel vault rooflights, and panelglazing systems). GRP is also used for profiled in-plane rooflights in metal roofs or as stand alonecanopies, and ETFE is an alternative whereextremely lightweight structures are required,e.g. for some atria. Additional design guidancefor each of these glazing materials is givenbelow.



Glass

Glass is usually used in skylights or panel glazingsystems. It is generally supplied as flat doubleglazed units (air or gas filled) designed to beinstalled into an aluminium support frame –either factory assembled into a completerooflight unit, or assembled on site into glazingbars. Glass is available in a wide range ofspecifications, but generally offers:

• The best acoustic insulation of any glazingmaterial.

• Outstanding durability.

• Excellent thermal insulation (although care isrequired to ensure the frame matches theperformance of the glazing).

• High light transmission (although care isrequired to avoid potential solar glareproblems with direct, non-diffused light).

The following should be considered whenspecifying glass rooflights:

• The glazing shall conform to the Centre forWindow and Cladding Technology (CWCT)Technical Note 42, minimum type 2.

• Careful consideration must be given to thebreakage characteristics of the specified glass.Laminated glass must be specified for theinner pane to avoid the risk of falling glassafter a breakage.

• Any toughened glass specified shall be heatsoaked tested.

• Guidance on loadings is available in BS 5516and BS 6399 part 2 and 3.

• Manufacturers’ advice should be sought withregard to correction factors for stated u-valuesof glass as they are determined in the verticalplane. Heat loss and thermal stress is higher ininclined glazing.

Polycarbonate

Polycarbonate is the most commonly usedmaterial for dome type rooflights, and is alsofrequently used in skylights, panel glazingsystems and barrel vault rooflights. It is availableas:

• Solid sheets which can be thermo formed tocreate individual dome rooflights orcontinuous barrel vault rooflights.

• Extruded flat solid or multiwall sheets whichcan be installed into an aluminium supportframe (either factory assembled into acomplete rooflight unit, or assembled on siteinto glazing bars),or which can be cold curvedand fitted into an aluminium frame to createbarrel vaults.

Polycarbonate is available in a wide range ofspecifications, but generally offers:

• Excellent thermal performance – whencorrectly specified.

• Excellent strength and non-fragilitycharacteristics (although care is required toensure correct design of frame/materialfixing).

• Good durability (service life typically 15-25years).

• High levels of light transmission when used asa clear material. Diffusing grades are alsoavailable.

The following should be considered whenspecifying polycarbonate rooflights:

• Manufacturers shall be consulted with regardto UV protection and the life expectancy ofthe sheet with regard to structural stabilityand discolouration. A manufacturers warrantyshall be sought for the life expectancy andagreed as acceptable with the School/LocalAuthority.


• The effects of fire are important whenspecifying plastic rooflights, the rooflightsmust conform to Building Regulations asstated in the performance in fire section onpage 26.

• Advice on plastics glazing is contained in BS6262 and from the Glass and GlazingFederation.

• Plastics, unlike glass, are partially permeable towater vapour. It is recommended, therefore,that ventilation should be provided in theconstruction of each glazing unit.

• Adequate provision is made to allow forthermal expansion/contraction - gaskets,sealants and primers must be approved forthe purpose by the manufacturer.

• When installed in glazing bars, adequaterebate depth must be provided which givesclearance to allow for thermal movement andedge cover sufficient to accommodate flexureunder wind or impact loadings asrecommended by manufacturer.

• The manufacturer’s advice must be followedwhen cutting or machining plastics glazingsheet so that impact resistance is notimpaired.

• Care shall be taken to assess the compatibilityof polycarbonate sheets with adjacent roofmaterials. Some roofing sheet finishes such asplastisol coated steel can over time affect themechanical performance of the product andan appropriate isolating system should beused.

GRP

GRP rooflights are generally profiled sheets,which form in-plane rooflights by replacing oneor more profiled metal sheets within a pitchedor, curved roof slope. They can also be used tocreate pitched canopies, and pre-curved GRPsheets can be used to form barrel vaultrooflights.

GRP rooflights generally offer:

• Excellent durability (service life typically over25 years).

• High levels of light transmission combinedwith high levels of diffusion for even lightdistribution without harsh shadows.

• Excellent thermal performance (whencorrectly specified).

• Excellent strength and non-fragilitycharacteristics (when correctly specified).

The following should be considered whenspecifying GRP rooflights:

• Manufacturers shall be consulted with regardto UV protection and the life expectancy ofthe sheet with regard to structural stabilityand discolouration. A manufacturers warrantyshall be sought for the life expectancy andagreed as acceptable with the School/LocalAuthority.

• GRP rooflights must be installed in accordancewith manufacturers instructions.

• GRP rooflights are available in a range of fireratings, so fire rating must be correctlyspecified to conform to Building Regulationsas stated in the performance in fire section onpage 26.


Ethylene Tetra Fluoro Ethylene (ETFE) Rooflights

ETFE rooflights are more specialised than otherrooflight systems. They comprise 2 or 3 ETFE(Ethylene Tetra Flouro Ethylene) films held in analuminium frame, inflated with a permanentpressurisation system to create pneumatic‘cushions’.

The main advantage of ETFE rooflights is theirlight weight (with associated low embodiedenergy) and ability to span large distances,which can make them suitable for somecourtyard and atrium applications (althoughother rooflights are also often suitable for suchapplications). They are usually less suitable formost other rooflight application on schools.

The following should be considered whenspecifying ETFE roofs:

• ETFE rooflights can be relatively easilydamaged or vandalised so should not be usedat low level, be easily accessible or used insituations where they are likely to be subjectto malicious damage.

• ETFE offers very low levels of acousticinsulation. The use of rooms below ETFErooflights shall be considered with regard tocompliance with the indoor ambient noiselevels and intrusion of rain noise as discussedin the acoustic section of this report. AnAcoustic expert should be consulted as rainsuppressors may be required in order for theETFE roof to be acceptable in certain areas ofthe School.

• In general ETFE has good durability butmanufacturers should be consulted to ensureit is not affected by UV light, atmosphericpollution and other forms of environmentalweathering in a particular location

• The long term performance of ETFE rooflightsis dependant on reliable operation of theinflation unit. Consider the location andmaintainability of the inflation unit.

• A rigorous maintenance routine must be inplace for the pressurisation system.

• The design should consider the affect ofpower failures and requirements for back upgenerators – consult manufacturers for details.

• The effects of fire are important whenspecifying plastic rooflights, the rooflightsmust conform to Building Regulations asstated in the performance in fire section onpage 26.

• The fire load must be low in the area coveredby ETFE. The location of ETFE rooflights mustnot aid the spread of fire, or the products ofcombustion to adjacent buildings and shallnot be carried over compartment walls.

• Always consult the Building Insurers at thedesign stage when specifying ETFE rooflightsfor their views on the risks presented as theremay be underwriting or excess issues.

• Consult Building Control and the BuildingInsurers for requirements of fire detection andsprinklers where ETFE rooflights are specified.

• ETFE can be overprinted with a variety ofsurface patterns / treatments to reduce solargain.


Durability

One of the key aspects of a product’senvironmental impact is its durability. This isexpressed in terms of anticipated life untilrenewal. It can also be expressed as the periodover which the combined initial cost andmaintenance cost exceeds the effectiveannualised cost of a replacement system. In normal circumstances, the durability of roofs depends on design and construction, the environment, material performance androutine maintenance.

In school buildings, the roof deck and insulationmust have a minimum lifetime of 60 years, withthe roof covering lasting a minimum of 30years. It should also be possible after the 30 years for the roof covering to be overlaid,overcoated, upgraded or readily replaced.Evidence must be provided by the roofcovering manufacturer from an independentEuropean accredited test authority that theabove minimum lifetime can be achieved.

As discussed in ‘Design standards’ on page 21,consideration should be made in the perimeterdetail for any upgrades to the insulationrequired by the current Building Regulations to achieve U-values current at the time of re-covering.

The roof should be inspected at intervals asrecommended by the manufacturer of the roofcovering and no longer than on an annualbasis. Any accumulation of debris should beremoved from roofs and cleaned/repaired ifnecessary as recommended by the roofcovering manufacturer under the duty of careof the building owner.

All coverings will degrade when exposed to theelements, the rate depending on how severe

the environment is in terms of:

• UV/solar degradation.

• Temperature stability.

• Industrial or marine pollution/resistance toacid rains, oil products.

• The presence and retention of moisture.

• The colour – lighter colours remain morestable than darker colours.

For designation of areas within the UnitedKingdom for wind and rain severity, consult BS 6399, Part 2.

As most durability problems can be associatedwith roof penetrations, robust details must bedeveloped with the roof covering manufacturerto ensure the design life of the roof covering isnot impaired around all penetrations.

All these factors must be taken into accountand recommendations from manufacturersobserved to achieve the design lives statedabove.


Health, safety, maintenance andguarantees

Health and safety

Construction of the roof is one of the mosthazardous operations because of the potentialfor falls or materials/components droppingonto people below.

In accordance with the Health and Safety atWork Act and the CDM Regulations (2007), abuilding has to be designed with safety in mind,not only for the construction period, butthroughout its normal operational life. Theclient, designer, principal contractor, roofingsub-contractor and CDM coordinator must planand document a safe system of work beforestarting construction, taking into account thefragility of the cladding systems. While fullyfixed metal sheeting is generally regarded asnon-fragile, many metal lining panels and rooflights must be treated with care, according toNARM Guidance Note 2003/1. Only metal liningsheets to ACR(M)001:2005 – roof fragility class Bor better are acceptable.

The HSE document HSG 33, Safety in roof workrefers specifically to fragile roof lights as anexample of a potential hazard. All rooflightsshould be considered as fragile, as they may be non-fragile when installed but after beingexposed to UV light their classification canchange to fragile. The following guidanceapplies to rooflights; and guarding should be considered to all rooflights:

• ACR(M)001:2005 – minimum roof fragility classB for thermoplastic rooflights.

• Centre for Window and Cladding Technology(CWCT) Technical Note 42, minimum type 2for glass rooflights.

Additional guidance relating to working atheights and with fragile materials can beobtained from ACR (Advisory Committee for Roofwork).



CDM regulations (2007) extend theresponsibility of health and safety to thedesigner to minimise risk during construction,maintenance and repair. To ensure safety onroofs during the life of the building, thefollowing HSE guidance should be followed inorder of priority:

a) Design out the need to gain access to theroof.

– Locate plant elsewhere.

– Eliminate in-board rainwater gutters.

– Provide suitable external access for MEWPfor activities, such as cleaning rainwateroutlets and general inspection work.

– Provide glazing that can be cleaned frominside the building.

b) Provide guard railing or parapet to perimeterand stairs/door access (if not reasonablypracticable to design out access on to theroof).

– This is the minimum provision wheremaintainable plant is located at roof level.

c) Provide a travel restraint system (if notreasonably practicable to provide guardrailing or parapet to perimeter andstairs/door access).

– Travel restraint is not acceptable for accessto maintainable plant.

Assessment of what is reasonably practicablemust take account of the nature ofmaintenance operations, including frequency,duration and duty. (Refer to CIRIA GuidanceC611: Safe access for maintenance and repair.)

On completion of the building, a health andsafety file must be issued by the CDM co-ordinator to the building owner. The followingmust be included in the health and safety file:

• Access to the roof to be restricted tocompetent persons or those under theirresponsibility.

• Roof light specification, including its non-fragile test method and weight – see ACR RedBook for information.

Maintenance and repairs

Routine inspection of the roof should be carriedout at least annually and preferably both inearly spring and late autumn. The purpose ofthe inspection is to:

• Check for damage.

• Ensure rainwater outlets are not obstructedand serviceable.

BS 7543, 8210 and BS ISO 15686 identify that asa minimum the following maintenance regimemust be undertaken:

a) Continuous regular observation by thebuilding user.

b) Annual visual inspection by qualifiedpersonnel.

c) Full inspection by qualified personnel everyfive years.


They also recommend that the maintenancecycle is established when the design is beingdeveloped.

Additional inspection must be carried out ifrequired by the roof covering manufacturer’swarranty included in the O&M manuals.

Inspections should be able to be carried outsafely and wherever possible from an externalMEWP, eliminating the need to access the roof.

Since all green roofs require highermaintenance levels than a traditional roof finishto keep them thriving, it is advisable to includethe cost of post-installation maintenance for anagreed period by appropriate contractors withinthe tender documents. The ongoingmaintenance requirements must be obtainedfrom the green roof system manufacturer toensure the building owner is aware of themaintenance requirements for this type of roof.

Before any remedial/new works are undertakento an existing roof (including the formation ofnew holes), the following should be ascertained:

• The original roof covering specification.

• The structure’s load bearing capacity andwhether it is capable of taking additional load.

• Whether any load limitations should beimposed during re-roofing.

• Kerb heights.

• Any implications for the existing guarantee orwarranty of the roof.

In all cases, the original roof coveringmanufacturer must be consulted.

Guarantees and warranties

A guarantee or warranty for the roofcovering/system must be put in place by theroofing sub-contractor directly between theclient and roof covering manufacturer. This willresult in the client having a single point fullycomprehensible warranty for the installedproduct.

Over and above this, the client can obtain FSA-approved insurance protecting againstinsolvency of the roofing contractor.

It is for the client or financial body to decide thelevel of provision and length of warrantyrequired, based on their particularcircumstances, to ensure the best long-termprotection.

The guarantee period should not be confusedwith the system durability period that is statedon certificates provided by European accreditedtest houses or the BRE green guide, ordemonstrated by historical evidence. Thedurability period is the expected life of aproduct but does not give any guarantees thatthis will be achieved.


Cost Comment

Capital costs

The roof element typically comprises between7-12% of the total building cost and oftenaccounts for a spend running into seven figuresfor a large secondary school when theassociated roof deck, drainage, rooflights andsafety access systems are taken into account.

The elemental costs of roofs per m2 of grossinternal floor area (GIFA) vary widely fromproject to project, reflecting the significantdifferences in the planning and organisation ofthe floor plans they cover and the specificationof the roof structure. In general, three-storeyschools demonstrate better cost efficiency forroofs than more extensive two-storey or singlestorey plans.

At the lower end of the cost range, three-storeystructures with simple specifications will cost inthe region of £75-£80m2 GIFA, while schoolswith more complex roof geometries, largersurface areas, steps, overhangs or similar designfeatures will cost upwards of £100m2, oftenreaching £150-160m2 GIFA and sometimes inexcess of the £200m2 GIFA for more iconic orunusual structures.

The extent of natural daylight to be deliveredinto the building through the roof is also asignificant cost driver. A sample of recentschemes identified that on average 6-15% ofthe total roof surface area in a typical secondaryschool is made up of some form of roof glazing.

Whole-life costs

Whole-life costs are crucial to the design,procurement, selection and maintenance ofroof coverings. Whichever specification ischosen, an holistic approach to decision makingwill deliver maximum benefits, as opposed toroofing selected on capital cost criteria alone.Factors to be taken into account include:

• Acoustic attenuation requirements at siteswith high noise pollution.

• Life span and replacement cycles of materials.

• Availability of system warranties/productguarantees.

• Susceptibility to damage and repairs (e.g.through high winds).

• Sustainability (e.g. transport, embodiedenergy, recycling).

• Buildability and programme sequence toweather tightness.

• Complexity of roof detailing to perimeters,penetrations, gutters, parapets, etc.

Professional advisers should take due regard ofthese factors and carry out option appraisals indeveloping project budgets. For guidance onthe approach to option appraisals, see HMTreasury’s Green Book Appraisal and evaluationin central government, at: www.hm-treasury.gov.uk/economic_data_and_tools/greenbook/data_greenbook_index.cfm

The specifications proposed in this documentare assessed to be cost neutral in relation tomost existing best practice solutions.


This section provides a summary of the

minimum performance requirements

for roof coverings together with

examples of roof covering types. This

does not preclude the designer from

using other roof finishes to achieve

particular aesthetic effects. However,

the alternative proposed roof covering

must conform to the key performance

requirements for the area where it is

intended to be used.

The DCSF considers that the examples wouldsatisfy the standard performance specification.However, the examples are provided forguidance purposes only. Users will be expectedto use their own skill and expertise in decidingwhat will be a reasonable and appropriate finaldesign solution in any situation. The DCSF doesnot accept responsibility for any losses sufferedas a result of the guidance provided in thisdocument.

N.B. In order to achieve the minimum carbonimprovement levels for school buildings asdetermined by Building Regulations L2A (2006edition), a combined improvement in fabric,heating, ventilation, lighting and airconditioning (where applicable) performancestandards are required. In order for design U-values for roofs to reasonably contributetowards the 23% improvement, it is consideredgood practice to exceed the limiting insulationstandards denoted by Table 4 of ApprovedDocument L2A.

Performance specifications and examples


Minimum performance requirements

Minimum performanceRequirement

0.25 W/m2K – weighted average (Building Regulations Part L2, 2006)

Thermal performanceof roof covering

Reference page

Page 21

2.2 W/m2K – weighted average (BuildingRegulations Part L2, 2006)

Thermal performanceof rooflights

Page 21

10m3/(h.m2) at an applied pressure of 50 Pascals(Building Regulations Part L2, 2006)

Air permeability Page 23

As Table 1.1 BB93 and BB101Indoor ambient noise level

Page 24

The increase in criteria for noise intrusion fromexternal sources during ‘heavy’ rainfall should notexceed the levels defined in Table1.1 BB93 by morethan 20dB in the design calculations provided byindependent acoustic consultants

Rain noise Page 24

Class 1 to BS 476 Part 7 or EU Class C-s3, d2 or better

Fire internal surfaces Page 25

AA, AB or AC to BS 476 Part 3 or EU Class B roof (T4) to ENV 1187 Part 4

Fire external surfaces Page 25

60 years for roof deck and insulation

30 years for roof covering, to be easily overlaid,overcoated, upgraded or replaced withouteffecting the insulation/deck below, when assessedby a competent technical professional. Evidencemust be provided by the roof coveringmanufacturer from an independent Europeanaccredited test authority or historical data that theabove minimum lifetime can be achieved

Minimum lifetime Page 33

Examples of roof covering solutions

Continuously supported roof coverings


TYP

E 1

Reinforced bitumen membranesGenerally, two working layers are applied on site, each consisting of a reinforcing base ofpolyester or a polyester/glass fibre mix, saturated and coated with polymer-modifiedbitumen. Many substrates also require a preparatory layer – check with manufacturer.Supplied in roll form, and commonly bonded with bitumen or specialist adhesives.

Acceptable construction

Specificstandards

Notes

Warm orinvertedflat roofs (seeroof pitchpage 15)

BS 6229

BS 8217

BS 8747

BS EN13707

Durability

The key qualities that are inherent in reinforced bitumen membrane systems and deliverproven durability are:

• The ability to withstand movement: daily thermal cycling, for example, may subjectroof coverings to temperature ranges of around 100°C.

• Resistance to weathering, mechanical damage, puncturing and tearing: most roofs aresuitable for light maintenance traffic; however, roof access should always be minimised.Where heavier traffic is expected, additional protection such as purpose-made walkwaysshould be provided, for example to service roof-mounted equipment.

The Flat Roofing Alliance (FRA) recommends that both working layers of the built-upmembrane should be polyester based, particularly where there is access to the roof.

Design factors that can further enhance durability include:

• Design roof falls to be twice the minimum – at least 1 in 40 – to ensure efficientdrainage of water.

• For green or inverted roofs, the membrane’s waterproof integrity must be ensuredbefore covering with ballast. N.B. If a green roof or inverted roof leaks, the repair costmay be significantly higher than a traditional system, so it is prudent to undertake anelectronic integrity test on the finished waterproofing system prior to burying it.

Health and safety

Hot bitumen bonding with associated health and safety risks – see Flat Roofing Alliance(FRA) information sheet 18 and HSE Guidance Note EH40.

Consideration must be given to the supporting substrate with regard to fragility andproviding a safe working environment, as required by CDM regulations.

Environmental

Good – low toxicity, recyclability, high material efficiency; CEN classifies bitumen as awaste material.

Bad – non-reusable, medium/high embodied energy, non-renewable source.

Acoustics

If lightweight roof decks are used, additional acoustic treatment may be required to theroof deck soffit or ceiling within the room below. Accredited third party acoustic testdata required to confirm suitability of proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 Part 3 or EU Class B roof (T4) to ENV1187 Part 4.

Insulation: The use of combustible insulation within the roof construction or elsewherewithin the building could influence insurance terms. See page 26, Insurance requirements.

Green roof: It must be stressed that the importance of good maintenance and irrigationof green roofs must be considered, otherwise there is an inherent fire risk. See page 26.



TYP

E 2

Polymeric single ply membranesA manufactured sheet product consisting of a polymer based single ply roofingmembrane, which may be applied in fully adhered or bonded systems, bymechanical fastening and by loose laying with suitable ballasting.


Specificstandards

Notes

Warm orinvertedflat roofs (seeroof pitchpage 15)

BS EN 13956

BS 6229:2003

The Single-Ply RoofingAssociationprovidesmorespecificadvice inits single-ply roofingdesignguide.

Durability

Design issues that can improve the long-term performance:

• Light-coloured membranes reflect heat and help to reduce heat ageing of the membrane.They also reduce summer cooling loads.

• Ensure differential movement is not transferred to the membrane, by designing robustweatherproof or waterproof details as appropriate.

• Ensure full calculation of wind load by a competent person, irrespective of the method ofattachment of the waterproof membrane. Appropriate design safety factors must be applied.

• High quality sealing of side and head laps, flashings and terminations is essential. Solventwelded seams should be tested shortly after forming and any discrepancies should berepaired immediately to prevent future failures. All personnel welding membranes (either hotair or solvent) must have passed the membrane manufacturer’s approved training course.

• The waterproof membrane must be terminated at perimeters and at the base of upstandsby a mechanical restraint.

• Protected walkways must be provided as appropriate for the in-service access requirement.During the construction phase the roof must be protected appropriately and contractualresponsibility for it must be made clear. During service, access to the roof must becontrolled by a permit system.

• Ensure the membrane manufacturer’s maintenance advice (as stated in the O&M manual)is understood by all staff to avoid the use of inappropriate materials for any future repair.

• For green or inverted roofs, the membrane’s waterproof integrity must be ensured beforecovering with ballast. N.B. If a green roof or inverted roof leaks, the repair cost may besignificantly higher than a traditional system, so it is prudent to undertake an electronicintegrity test on the finished waterproofing system prior to burying it.

• Roof falls must be twice the minimum (at least 1 in 40) to ensure efficient drainage of water.

Health and safety

Consideration must be given to the supporting substrate with regard to fragility andproviding a safe working environment, as required by CDM regulations.

Environmental

Good – TPO, EPDM and PVC membranes are reusable, with low toxicity. PVC and FPO can bere-cycled. High material efficiency.

Bad – Derived from oil. UK recycling expected to commence only once post-consumervolumes become significant.

Acoustics

If lightweight roof decks are used, additional acoustic treatment may be required to the roofdeck soffit or ceiling within the room below. Accredited third party acoustic test data arerequired to confirm suitability of the proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 Part 3 or EU Class B roof (T4) to ENV 1187 Part 4.

Insulation: The use of combustible insulation within the roof construction or elsewhere withinthe building could influence insurance terms. See page 26, Insurance requirements.

Green roof: It must be stressed that the importance of good maintenance and irrigation ofgreen roofs must be considered, otherwise there is an inherent fire risk. See page 26.



TYP

E 3

Mastic asphaltMastic asphalt is a type of asphalt composed of suitable graded mineral matter andasphaltic cement in such proportions as to form a cohesive, impermeable mass,solid or semi-solid under normal temperature conditions, but sufficiently fluid whenbrought to a suitable temperature to be spread by means of a hand float or bymechanical means without compaction.


Specificstandards

Notes

Warm orinverted flatroofs (see roofpitch page 15)

BS 6229

BS 8218

Durability

To ensure a durable specification, it is recommended that high performancepolymer modified mastic asphalt is used, with a minimum requirement of masticasphalt manufactured in accordance with BS 6925, 1988 type R/988/T25.

Solar protection should be specified to warm roof constructions in accordance withmanufacturers’ recommendations.

For inverted roofs, the membrane’s waterproof integrity must be ensured beforecovering it up, as leaks will be difficult to locate after the insulation and ballast havebeen put in place.

Roof falls must be designed to be twice the minimum – at least 1 in 40 – to ensureefficient drainage of water.

Health and safety

The main hazard in using hot melt systems is the risk of severe burns to the skin –hence PPE should be used.

Refer to the Mastic Asphalt Council’s Technical Guide for extensive guidance onhealth and safety issues.

Consideration must be given to the supporting substrate with regard to fragilityand producing a safe working environment, as required by CDM regulations.

Environmental

Good – Recyclable, seamless and flexible in application.

Bad – Medium/high embodied energy, non renewable resource.

Acoustics

If lightweight roof decks are used, additional acoustic treatment may be required tothe roof deck soffit or ceiling within the room below. Accredited third partyacoustic test data are required to confirm suitability of proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 part 3 or EU Class B roof (T4) toENV 1187 Part 4.

Insulation: The use of combustible insulation within the roof construction orelsewhere within the building could influence insurance terms. See page 26,Insurance requirements.

Green roof: It must be stressed that the importance of good maintenance andirrigation of green roofs must be considered, or there is an inherent fire risk. Seepage 26.



TYP

E 4

Hot melt waterproofing systemsHot melt bitumen membranes, hot applied by rubber bladed squeegee, consistingof primer, modified bitumen laid in two coats with polyester reinforcementinterleaving. A solar protection or access sheet is applied to the top surface,depending on the end use.


Specificstandards

Notes

Inverted flatroofs (see roofpitch page 15)

BS 6229

No specificBritishStandards see FRA infosheet 31.

Durability

Key issues of durability are:

• The substrate construction and condition must be free from material that couldimpair the bond, or create thin spots or penetrations in the coating.

• There must be provision for moisture removal of damp substrates.

• There must be no point loads on the roof.

• The system specified must be suited to the expected traffic.

• There must be appropriate detailing at edges, verges, upstands, outlets,movement joints and day joints.

• Avoidance of air holes is essential.

• Design roof falls must be twice the minimum – at least 1 in 40 – to ensureefficient drainage of water.

• As hot melt waterproofing systems are always buried under inverted roofs, greenroof or podium deck waterproof integrity must be ensured before covering it up,as leaks will be difficult to locate after the insulation and ballast have been put inplace.

Health and safety

The main hazard in using hot melt systems is the risk of severe burns to the skin –hence PPE should be used.

Consideration must be given to the supporting substrate with regard to fragilityand producing a safe working environment, as required by CDM regulations.

Environmental

Good – High material efficiency, recycled material in product, recyclable.

Bad – Not reusable but recyclable, medium embodied energy, non-renewablesource.

Acoustics

If lightweight roof decks are used, additional acoustic treatment may be required tothe roof deck soffit or ceiling within the room below. Accredited third partyacoustic test data are required to confirm suitability of proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 Part 3 or EU Class B roof (T4) to ENV 1187 Part 4.

Insulation: The use of combustible insulation within the roof construction orelsewhere within the building could influence insurance terms. See page 26,Insurance requirements.

Green roof: It must be stressed that the importance of good maintenance andirrigation of green roofs must be considered, or there is an inherent fire risk. Seepage 26.



TYP

E 5

Malleable sheet metal roofingMalleable sheet roofing consists of sheet metals such as copper, lead and zincwhich require a substrate such as ply wood for support. The roofing requiresparticular attention to the junction and perimeter details, and is usually used for aparticular aesthetic finish.


Specificstandards

Notes

Warm & coldpitched roofs(see roof pitchpage 15)

Aluminium

BS EN 485, 515and 573

Copper

BS EN 504,1172

Zinc

BS EN 988

Stainless steel

BS EN 502,10088-2, 10258and 10259

Durability

Key factors are:

• Failure of aluminium coverings and flashings can be caused by restraint ofmovement, fatigue of fixings, use of inadequate substrates, or exposure tounsuitable aggressive atmospheres. The risk of premature failure is minimised bygood design and specification.

Electrolytic corrosion and chemical attack can occur on cladding, flashings, fixings,gutters, etc. when exposed to other materials in moist conditions andcontaminated liquid. Always consult the roof covering manufacturer to ensurecompatibility, particularly with the substrate.

It is essential to avoid the risk of underside condensation and corrosion byadopting forms of construction and ventilation that allow for removal of moisture.

Health and safety

Consideration must be given to the supporting substrate with regard to fragilityand providing a safe working environment, as required by CDM regulations.

Environmental

Good – Recyclable, may have recycled content, high material efficiency.

Bad – high embodied energy, limited source, greenhouse gases, some metals toxicin use.

Acoustics

Treatment may be required to the roof deck soffit or ceiling within the room belowto meet acoustic requirements. Accredited third party acoustic test data required toconfirm suitability of proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 part 3 or EU class B roof (T4) toENV 1187 Part 4.

Insulation: The use of combustible insulation within the roof construction orelsewhere within the building could additionally influence insurance terms. Seepage 26, Insurance requirements.



TYP

E 6

Slating/tilingTiled roofing, generally consisting of clay, concrete, natural slate, resin-slate or fibre cement tiles fixed to roofing battens on timber rafters

The roof design can be either of warm or cold construction, with a roofingunderlay, insulation and vapour control layer.


Specificstandards

Notes

Warm or coldpitched roofs(see roof pitchpage 15)

BS 5534Durability

Key factors include:

• Good ‘nesting’ of slates/tiles enhances the weather tightness and reduces the riskof capillary action.

• The combination of roof pitch, profile depth and size of laps is significant whenconsidering water penetration and must always be in accordance withmanufacturers’ recommendations.

• Fragility is the principal concern: slates/tiles are vulnerable to breakage and mustbe protected during roof maintenance.

• Pitch and rafter lengths are critical to achieving a water tight solution; theminimum and maximums must always be checked with the roof coveringmanufacturer.

• Long spans are achievable with profiled interlocking tiles, for which there are norafter length restrictions.

Health and safety

Consideration must be given to a safe working environment and falls from heightsthrough open discontinuous support structures, as required by CDM regulations.

Environmental

Good – Reusable and recyclable, may have recycled content, high materialefficiency, low toxicity (except fibre cement tiles which are high), low embodiedenergy (except clay and slate tiles).

Bad – Greenhouse gases in concrete and fibre cement tiles, high toxicity inconcrete and fibre cement tiles, high embodied energy in clay and slate tiles, lowUK reserves in slate tiles.

Acoustics

Treatment may be required to the roof deck soffit or ceiling within the room belowto meet acoustic requirements. Accredited third party acoustic test data required toconfirm suitability of proposed construction.

Fire

Membrane/roof covering: AA, AB or AC to BS 476 part 3 or EU class B roof (T4) to ENV 1187 Part 4.

Insulation: The use of combustible insulation within the roof construction orelsewhere within the building could additionally influence insurance terms. Seepage 26, Insurance requirements.

Discontinuously supported roof coverings



TYP

E 7

Profiled sheetingProfiled roof sheeting is generally a built-up system consisting of a metal liner tray,insulation and a metal top sheet, either in natural form such as mill finishedaluminium, or colour coated with a proprietary system. The system is supported onmetal purlin rails and the top sheet is often a standing seam roof with no exposedfixings, which can achieve low pitches.


Specificstandards

Notes

Warm roofs onall roof pitchesgiven thatproperinstallationmethods areused (see roofpitch page 15)

BS 5427-1Durability

Key factors are:

• The risk of water penetration in profiled sheet roofs increases as the pitch islowered; therefore, always consult the covering manufacturer for minimum pitchand suitable detailing.

• Electrolytic corrosion and chemical attack can occur on cladding, flashings,fixings, gutters, rooflights etc. when exposed to other materials in moistconditions and contaminated liquid. Uncoated steel (for example, cut edges,aluminium and stainless steel) can be affected. Avoidance is by selecting suitablematerials, good detailing and the use of isolating techniques. Always consult roofcovering manufacturer to ensure compatibility and establish good detailing.

See MCRMA Technical Paper 12 for details about the types and use of fasteners.

• Some durability issues apply to all types of organic coated cladding. The amountof time the coating lasts before painting is needed is largely related to theultraviolet light dosage and the environment it is located in – polluted or marineenvironments tend to reduce coating durability.

Health and safety

Consideration must be given to a safe working environment and falls from heightsthrough open discontinuous support structures, as required by CDM regulations.Additionally, the support decks fragility must be considered. See page 34 of thisdocument.

Environmental

Good – Recyclable, may have recycled content, high material efficiency.

Bad – high embodied energy, some products from limited source.

Acoustics

The sound absorbing qualities of cladding systems can be improved by using asound absorbing lining or a perforated metal lining backed with sound absorbingmaterial such as mineral wool. This may be required to meet acousticrequirements. Accredited third party acoustic test data are required to confirmsuitability of proposed construction.

Fire


Insulation: Combustible thermoplastic insulation material should not be carriedover the compartment wall, as a core to double-skinned roof sheeting or otherwise.The use of combustible insulation within the roof construction or elsewhere withinthe building could additionally influence insurance terms, though insulated paneland cladding systems that have LPCB certification are accepted. See page 26,Insurance requirements.



TYP

E 8

Insulated panelsInsulated roofing panels are single piece factory pre-engineered metal facedpanels, consisting of metal internal facing, integral insulation and a profiled metaltop sheet. The panels come to site as a unit and are mechanically fixed to metalpurlins. The internal and external faces are colour coated with a proprietary system.These are ideally suited to low pitches and long spans.


Specificstandards

Notes

Warm Roofs on all roofpitches giventhat properinstallationmethods areused (see roofpitch page 15)

BS 5427-1Durability

Key factors are:

• The risk of water penetration in insulated panel roofs increases as the pitch islowered; therefore, always consult the covering manufacturer for minimum pitchand suitable detailing.

• Electrolytic corrosion and chemical attack can occur on cladding, flashings,fixings, gutters, rooflights, etc. when exposed to other materials in moistconditions and contaminated liquid. Uncoated steel (for example cut edges,aluminium and stainless steel) can be affected. Avoidance is by selecting suitablematerials, good detailing and using isolating techniques. Always consult the roofcovering manufacturer to ensure compatibility and establish good detailing.

See MCRMA Technical Paper 12 for details about the types and use of fasteners.

• Some durability issues apply to all types of organic coated cladding. The amountof time the coating lasts before painting is needed is largely related to theultraviolet light dosage and the environment it is located in – polluted or marineenvironments tend to reduce coating durability.

Health and safety

Consideration must be given to a safe working environment and falls from heightsthrough open discontinuous support structures as required by CDM regulations.

Environmental

Good – High material efficiency.

Bad – High embodied energy, some coatings contain PVCs, unrecyclable,unreusable.

Acoustics

Treatment will be required to the roof deck soffit or ceiling within the room belowto meet acoustic requirements. Accredited third party acoustic test data arerequired to confirm suitability of proposed construction.

Fire


Insulation: Combustible thermoplastic insulation material should not be carriedover the compartment wall, as a core to double-skinned roof sheeting or otherwise.The use of combustible insulation within the roof construction or elsewhere withinthe building could additionally influence insurance terms, though insulated paneland cladding systems that have LPCB certification are accepted. See page 26,Insurance requirements.

Green roof: It must be stressed that the importance of good maintenance andirrigation of green roofs must be considered, otherwise there is an inherent fire risk. See page 26.



References

This document was published in

January 2008. After this date readers

should ensure they use the latest

edition of all references.

Typical constructions• British Board of Agreement certificates at

www.bbacerts.co.uk

• BS 6229 Code of practice for flat roofs withcontinuously supported coverings

• BS 6915 Design and construction of fullysupported lead sheet roof and wall coverings –Code of practice

• BS 8218: 1998 Code of practice for masticasphalt

• BS 8747

• Building Bulletin 101 Ventilation of schoolbuildings

• CIRIA C644 Building greener – Guidance on theuse of green roofs, green walls andcomplementary features on buildings

• Flat Roof Alliance (FRA) Roofing handbook

• Flat roofing: a guide to good practice, published by Ruberoid, version 4 2007

• MRCMA Technical Paper TP9, Composite roofand wall cladding panel design guide(June 1995)


• National Association of RooflightManufacturers (NARM) Designing withrooflights: Supporting the guidance in AD L2A & AD L2B, 2006

• NBS Standard Guidance

• Rolled lead sheet – The complete manual(available from Lead Sheet Association)

• SCI Publication P346 – 2006 ‘Best practice forthe specification and installation of metalcladding and secondary steelwork, SteelConstruction Institute publication, preparedjointly with EPIC and MCRMA

• SPRA Design guide to single ply roofing, 2007

• The Mastic Asphalt Council’s Technical guide

Thermal • BRE IP 1/06 Assessing the effects of thermal

bridging at junctions and around openings in the envelope

• BREEAM Schools 2006, Assessor Manual,Energy – Reduction of CO2 emissions Creditreference number E1

• Building Regulations Approved Document L2 Conservation of fuel and power(2006 edition)

• EPIC Insulated panels for external roof and wallcladding – Guidance on compliance with theconservation of fuel and power BuildingRegulations, 2006

• Guidelines for environmental design in schools,DfES School Buildings and Design Unit. Thispublication is available in the RegulatoryInformation Section of the DCSF SchoolBuildings and Design Unit’s website atwww.teachernet.gov.uk/energy

• MRCMA/EPIC – Technical Paper TP17 (2007),for cladding systems Design guide for metalroofing and cladding to comply with energyrequirements of UK Building Regulations, 2006

• National Association of RooflightManufacturers (NARM) Designing withrooflights: Supporting the guidance in AD L2A & AD L2B, 2006

Acoustics• Acoustic design of schools, DCSF. The

Stationery Office, 2003 ISBN 0 11 271105 7.This publication is available in the RegulatoryInformation Section of the DCSF SchoolBuildings and Design Unit’s website atwww.teachernet.gov.uk/acoustics

• BREEAM Schools 2006, Assessor Manual, Heath and wellbeing: Acoustic performanceCredit reference number HW17

• Building Bulletin 93, Acoustic design of schools:A design guide, DCSF

• Building Bulletin 101, Ventilation of schoolbuildings, DCSF

• Building Regulations Approved Document E Acoustics


Fire• BS 476: 1987 Fire tests on building materials

and structures

• BS 476 Part 3: 2004 Classification and methodof test for external fire exposure to roofs

• BS EN 13501: 2007 Fire classification ofconstruction products and building elements

• BS EN 13501-1: 2007 Fire classification ofconstruction products and building elements –Part 1: Classification from reaction to fire tests

• BS EN 13501-2: 2007 Fire classification ofconstruction products and building elements –Part 2: Classification from fire resistance tests

• BS EN 13501-5: 2007 Fire classification ofconstruction products and building elements –Part 5: Classification from external fire exposureto roofs tests

• Building Bulletin 100 Design for fire safety in schools

• Building Regulations Approved Document B – Fire safety

• Design guide for the fire protection of buildings –Essential principles in fires, published by the Fire Protection Association

• EPIC Insulated panels for roof and wall cladding: A guide to fire safety, specification and installation

• HMSO Fire safety risk assessment in educational premises, 2006

• LPC Design guide for the fire protection ofbuildings, 2000

• LPS 1181: Part 1: Issue 1.1, Series of fire growth tests for LPCB approval and listing ofconstruction product systems, Part 1:Requirements and tests for built-up cladding and sandwich panel systems for use as theexternal envelope of buildings

• MRCMA Technical Paper TP6 Profiled metalroofing design guide

General requirements• BS EN 501, 502, 504 to 508 and 1304

Product standards for tiles and slating

• BS 5427-1 Product standard for profiledcladding

• BS 5534 Product standard for slating and tiling

• BS 6229 Code of practice for flat roofscontinuously supported

• BS 8000 Workmanship on site

• BS 8217 Code of practice for built-up felt roofs

• BS 8219 Code of practice for profiled fibre cement tiles

• Advisory Committee for Roofwork –ACR[M]001:2005 Test for non-fragility of profiledsheeted roofing assemblies [third edition]

• ACR [CP] 002:2005 Guidance note for safeworking on fragile roofs covering the designing,planning and carrying out of inspection,maintenance, repair and refurbishment work

• BS 6651: 1991 Code of practice for theprotection of structures against lightningSixteenth edition

• CDM Regulations (2007)


• CP 143-1,5,10,12 &15 Sheet roof and wallcoverings code of practice

• ForschungsgesellschaftLandschaftsentwicklung Landschaftsbau e.V.(FLL) www.f-l-l.de

• Green guide to specification, Blackwell Science

• Health & Safety at Work Act

• HSE publication HSG33 health and safety inroof work

• Manufacturers’ literature

• R10 General guidance NBS

Trade association links• EPIC [Engineered Panels in Construction]

www.epic.uk.com

• EURISOL (UK Mineral Wool Association)www.eurisol.com

• Flat Roofing Alliance (FRA) www.fra.org.uk

• Lead Sheet Associationwww.leadsheetassociation.org.uk

• Mastic Asphalt Councilwww.masticasphaltcouncil.co.uk

• MCRMA (Metal Roofing and CladdingManufacturers Association) www.mcrma.co.uk

• National Association of RooflightManufacturers www.narm.org.uk

• Single Ply Roofing Association,www.spra.co.uk

Supplementary acknowledgmentsA. Mackenzie, BauderA. Moore, RuberoidAdrian Fryer, RockwoolAlastair Kerr, Wood Panel Industries FederationAndrew. M, CeramfedBill Hawker, BrettmartinBill Parlor, Bill Parlor ConsultingClive Challion, Corus GroupCraig Smitth, RuberoidDave Sibert, Fire Protection AssociationDavid Lowe, SpeedDeckDuncan Johnstone, Corus KalzipGary Heath, Hambleside DanelawGraham Ellicot, ASFPGrenville Kitteridge, RadmatJ. Pearce, RuberoidJim Hooker, Single Ply Roofing AssociationJim Lowther, Xtralite (Rooflights) LimitedJohn Blowers, Mastic Asphalt AssociationJohn Thelwell, Kee klamp LimitedJohn Woods, Lead Sheet AssociationJonathan Arnold, Corus GroupJonathan Clemens, Corus KalzipJonathan K, SteadmansJustin Ratcliffe, CABKen Hamilton, Hamilton and LindsayKevin Ley, Lafarge Roofing

Mark Golder, SarnafilMark Miles, SarnafilMartyn Holloway, RockwoolMatthew Smith, ZurichMick Oliver, BBANeil Ware, Xtralite (Rooflights) LimitedNigel Blacklock, SarnafilNigel Rees, Glass and Glazing FederationNorman Richards, Marley EternitP. Gibson, CelotexP. Stonebridge, BauderPaul Franklin, Flat Roof AlliancePatrick Hall, Dow Building SolutionsPeter Trew, EPICPhilip Beswick, Cox Building ProductsPhilip Heath, Kingspan InsulationRichard Bromwich, Kingspan InsulationS. Farrow, TRAS. Revan, SwishStephen Wise, Knauf InsulationStuart Blackie, ZurichStuart Pocock, Lafarge RoofingTom Moon, EshaicopalMetal cladding and roofing manufacturersassociationNational association of rooflightmanufacturersWarrington fire consulting

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