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General principles and typical constructions are shown in this section.Space does not allow all details for each type of construction to be shown.

Many such details are illustrated and discussed in greater detail in Part E of theBuilding Regulations.[1] Further guidance and illustrations are also available in

Sound Control for Homes[2] and in manufacturers’ literature for proprietarymaterials and systems.

Sound insulation 3

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CT

ION

3.1 RoofsThe sound insulation of a pitched roofdepends upon the mass of the ceiling andthe roof layers and the presence of asound absorbing material in the roofspace. Mineral wool, used as thermalinsulation in the ceiling void, will alsoprovide some acoustic absorption, whichwill have a small effect on the overallsound insulation of a roof. A denserspecification of mineral wool ascommonly used for acoustic insulationwould have a greater effect on the overallsound insulation of the roof.

Where it is necessary to ventilate theroof space, it is advisable to make anynecessary improvements to the soundinsulation by increasing the mass of theceiling layer, which should be airtight.Recessed light fittings can make thisdifficult and sometimes it is better toplace the sound insulating material belowthe roof covering and to extend partitionwalls up to the roof layer (providingadequate ventilation can be maintained).

3.1.1 Rain noiseThe impact noise from rain on the roofcan significantly increase the indoor noiselevel; in some cases the noise level inside aschool due to rain can be as high as 70 dB(A).

Although rain noise is excluded fromthe definition of indoor ambient noise in

Section 1.1, it is a potentially importantnoise source which must be considered atan early point in the roof design tominimise disturbance inside the school.

Excessive noise from rain on the roofcan occur in spaces (eg sports halls,assembly halls) where the roof is madefrom profiled metal cladding and there isno sealed roof space below the roof toattenuate the noise before it radiates intothe space below. With profiled metalcladding, the two main treatments thatshould be used in combination to providesufficient resistance to impact sound fromrain on the roof are: • damping of the profiled metal cladding(eg using commercial damping materials) • independent ceilings (eg two sheets of10 kg/m2 board material such asplasterboard, each supported on its ownframe and isolated from the profiled metalcladding. Absorptive material, such asmineral fibre, should be included in thecavity.)

Profiled metal cladding used without adamping material and without anindependent ceiling is unlikely to providesufficient resistance to impact sound fromrain on the roof. A suitable system thatcould be used in schools is shown inFigure 3.1. The performance of such asystem was measured by McLoughlin etal[3].

Prediction models are available topredict the noise radiated from a singlesheet of material; however, a single sheetwill not provide sufficient attenuation ofimpact noise from rain. Suitablelightweight roof constructions that doprovide sufficient attenuation will consistof many layers. For these multi-layer roofconstructions, laboratory measured datafor the entire roof construction is needed.

Figure 3.1: Profiled metalclad roof incorporatingacoustic damping

Damped aluminium tiles

Plasticised steel top sheet

50 – 100 mm mineral fibreTwo sheets of Fermacell board

Steel liner panel50 – 100 mm mineral fibre

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At the time of writing, a new laboratorymeasurement standard for impact soundfrom rain on the roof, ISO 140-18[4], isunder development. In the future this willallow comparison of the insulationprovided by different roof, window andglazing elements and calculation of thesound pressure level in the space belowthe roof.

When designing against noise from rainon the roof, consideration should also begiven to any glazing (eg roof lights) inthe roof. Due to the variety of differentroof constructions, advice should besought from an acoustic consultant whowill be able to calculate the soundpressure level in the space due to typicalrainfall on the specific roof.

3.2 External WallsFor masonry walls, such as a 225 mmsolid brick wall, a brick/block cavity wallor a brick-clad timber frame wall, thesound insulation performance willnormally be such that the windows,ventilators and, in some cases, the roofwill dictate the overall sound insulation ofthe building envelope.

Timber frame walls with lightweightcladding and other lightweight systems ofconstruction normally provide a lowerstandard of sound insulation at lowfrequencies, where road traffic and aircraftoften produce high levels of noise. Thiscan result in a low airborne soundinsulation against these noise sourcesunless the cladding system has sufficientlow frequency sound insulation. Theairborne sound insulation can be assessedfrom laboratory measurements carried outaccording to the method of BS EN ISO140-3:1995[5].

3.3 VentilationThe method of ventilation as well as thetype and location of ventilation openingswill affect the overall sound insulation ofthe building envelope. When externalnoise levels are higher than 60 dBLAeq,30min, simple natural ventilationsolutions may not be appropriate as theventilation openings also let in noise.However, it is possible to use acousticallyattenuated natural ventilation rather than

full mechanical ventilation when externalnoise levels are high but do not exceed70 dB LAeq,30min.

The School Premises Regulations[6]

require that: "All occupied areas in a school building

shall have controllable ventilation at aminimum rate of 3 litres of fresh air persecond for each of the maximum number ofpersons the area will accommodate.

All teaching accommodation, medicalexamination or treatment rooms, sickrooms, sleeping and living accommodationshall also be capable of being ventilated at aminimum rate of 8 litres of fresh air persecond for each of the usual number ofpeople in those areas when such areas areoccupied."

In the case of the latter denselyoccupied spaces such as classrooms, 8litres per second per person is theminimum amount of fresh air that shouldbe provided by a natural or mechanicalventilation system under normal workingconditions, in order to maintain goodindoor air quality.

In order to satisfy the limits for theindoor ambient noise levels in Table 1.1,it is necessary to consider the soundattenuation of the ventilation openings sothat the building envelope can bedesigned with the appropriate overallsound insulation. In calculations of overallsound insulation the attenuation assumedfor the ventilation system should be fornormal operating conditions.

The main choices for the naturalventilation of typical classrooms areshown in Figure 3.2. Case Studies 7.8and 7.9 describe the recent application oftwo of these design solutions in newsecondary school buildings.

Additional ventilation such as openablewindows or vents may be required toprevent summertime overheating. Underthese circumstances an increase in internalnoise levels is expected and the levels inTable 1.1 may be exceeded depending onthe ventilation strategy.

3.3.1 VentilatorsPassive ventilators normally penetrate thewalls, but in some cases they penetrate thewindow frames (eg trickle ventilators) or

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Figure 3.2: Possibletypes of natural ventilation

Secondary glazing withstaggered openingsAcoustically treated high capacity air inlet

Secondary glazing with staggered openings

Absorbent duct liningorAcoustic louvres on outsideplus• secondary glazing with staggered openings• acoustically treated high capacity air inlet

CLASSROOMCORRIDOR 2.7 m

2.7 m

2.7 m

2.7 m

CROSS-VENTILATION

SINGLE-SIDED VENTILATION

STACK VENTILATION

WIND TOWER/BALANCEDFLUE VENTILATION

Absorbent duct liningAcoustic louvres on outsideSecondary glazing with staggered openingsAttenuator plenum boxElectronic noise

POSSIBLE SOUNDINSULATION MEASURES

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the windows themselves. Often windowsare not used as intended as they causeuncomfortable draughts. For this reason,increased use is being made of purposedesigned ventilation systems with orwithout acoustic attenuation.

Many proprietary products aredesigned for the domestic sector and insome cases they do not have large enoughopenings for classrooms and other largerooms found in schools. The acousticperformance of any ventilator can beassessed with laboratory sound insulationtest data measured according to BS EN20140-10:1992[7]. Because of thecomplexity of the assessment of theacoustic performance of a ventilator,advice may be needed from a specialistacoustic consultant. To maintain adequateventilation, it is essential that the effectivearea of the ventilator is considered as itmay be smaller than the free area (see prEN 13141-1[8]).

It is important, particularly in the caseof sound-attenuated products, that a goodseal is achieved between the penetrationthrough the wall or window and theventilator unit. Where through-the-wallproducts are used, the aperture should becut accurately and the gap around theperimeter of the penetrating duct shouldbe packed with sound insulating materialprior to application of a continuous,flexible, airtight seal on both sides.

In some schools bespoke ventilatordesigns, such as that shown in Figure 3.3,are needed. For more examples ofventilator solutions see Case Studies 7.8and 7.9.

3.4 External WindowsThe airborne sound insulation ofwindows can be assessed from laboratorymeasurements of the sound reductionindex according to BS EN ISO 140-3:1995[5]. When choosing suitablewindows using measured data, care mustbe taken to differentiate betweenmeasured data for glazing and measureddata for windows. The reason is that theoverall sound insulation performance of awindow is affected by the window frameand the sealing as well as the glazing.

To achieve the required sound

insulation with thin glass it is oftennecessary to use two panes separated byan air (or other gas) filled cavity. Intheory, the wider the gap between thepanes, the greater the sound insulation.In practice, the width of the cavity indouble glazing makes relatively littledifference for cavity widths between 6mm and 16 mm. Wider cavity widthsperform significantly better.

In existing buildings, secondary glazingmay be installed as an alternative toreplacing existing single glazing withdouble glazing. The effectiveness ofsecondary glazing will be determined bythe thickness of the glass and the width ofthe air gap between the panes. Anotheralternative may be to fit a completely newdouble-glazed window on the inside ofthe existing window opening, leaving theoriginal window intact. The use of soundabsorbing reveal linings improves theperformance of double-glazed windows,but the improvement is mainly in themiddle to high frequency region, where ithas little effect on road traffic and aircraftnoise spectra.

To achieve their optimumperformance, it is essential that theglazing in windows makes an airtight sealwith its surround, and that opening lightshave effective seals around the perimeterof each frame. Neoprene compressionseals will provide a more airtight seal thanbrush seals. The framing of the windowshould also be assembled to achieve anairtight construction.

It is equally important that an airtightseal is achieved between the perimeter ofthe window frame and the opening intowhich it is to be fixed. The openingshould be accurately made to receive thewindow, and the perimeter packed withsound insulating material prior toapplication of a continuous seal on bothsides.

For partially open single-glazedwindows or double-glazed windows withopposite opening panes, the laboratorymeasured airborne sound insulation isapproximately 10-15 dB Rw . Thisincreases to an Rw of 20-25 dB in theopen position for a secondary glazingsystem with partially open ventilation

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openings, with the openings staggered onplan or elevation, and with absorbentlining of the window reveals (see Figure3.3). In situ, the degree of attenuationprovided by an open window alsodepends on the spectrum of the noise andthe geometry of the situation.

The spreadsheet of sound reductionindices on the DfES website(www.teachernet.gov.uk/acoustics) givesvalues of Rw for various types of window,glazing thickness, and air gap. Indicationsare also given of the sound reductionindices of open windows.

3.5 External DoorsFor external doors the airborne soundinsulation is determined by the door set,which is the combination of door andframe. The quality of the seal achievedaround the perimeter of the door is

crucial in achieving the potentialperformance of the door itself. Effectiveseals should be provided at the threshold,jambs and head of the door frame. Aswith windows, neoprene compressionseals are more effective than brush seals,but their effectiveness will be stronglyinfluenced by workmanship on site. Brushseals can however be effective and tend tobe more hard wearing than compressionseals.

It is also important that an airtight sealis achieved between the perimeter of thedoor frame and the opening into which itis to be fixed. The opening should beaccurately made to receive the door frameand any gaps around the perimeter packedwith insulating material prior toapplication of a continuous, airtight sealon both sides.

A high level of airborne sound

Softwood framing toextend reveals

Sound-absorbing reveallinings to head and sides

Second casement openablefor cleaning only

Bottom hung casement,openable for ventilation,fitted with secure adjustable stay

Supporting framing below cill

Existing inward-opening light,movement to be restricted

Existing brickwork wall

200mm nominal

300mm nominal

Figure 3.3: Secondaryglazing producing astaggered air flow path

Retrofit secondary glazing producinga staggered air flow path. Designedto limit aircraft noise intrusion toscience laboratories at a secondaryschool near London City Airport.

A sound reduction of approximately 20-25 dB Rw was achieved using thisdesign.

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insulation is difficult to provide using asingle door; however, it can be achievedby using a lobby with two sets of doors,as often provided for energy efficiency, ora specialist acoustic doorset.

Calculations and tests for sound insulation of the building

envelopeThere are two methods by which it ispossible to calculate the indoor ambientnoise levels due to external noise.

The first method is to calculate theindoor ambient noise level according tothe principles of BS EN 12354-3:2000[9].An Excel spreadsheet to calculate thesound insulation of building envelopes,based on BS EN 12354-3:2000 isavailable via the DfES website(www.teachernet.gov.uk/acoustics). Theprinciples of this calculation spreadsheetare given in Appendices 5 and 6

The second method is to calculate theindoor ambient noise level using themeasured façade sound insulation datafrom an identical construction at anothersite.

3.6 Subjective characteristics ofnoiseThe indoor ambient noise levels in Table1.1 provide a reasonable basis forassessment, but some noises have tonal orintermittent characteristics which makethem particularly noticeable or disturbing,even below the specified levels. This ismost common with industrial noise. At aminority of sites, achieving the levels inTable 1.1 will not prevent disturbancefrom external industrial sources, andadditional noise mitigation may berequired. In these cases advice from anacoustic consultant should be sought.

The potentially beneficial maskingeffect of some types of continuousbroadband external noise (such as roadtraffic noise) must also be borne in mind,see Section 2.12. This noise may partiallymask other sounds, such as fromneighbouring classrooms, which may bemore disturbing than the external noise.There are acoustic benefits, as well as costbenefits, in ensuring that the level ofinsulation provided is not over-specified

but is commensurate with the externalnoise.

3.7 Variation of noise incident ondifferent facadesIt may be convenient to determine theexternal noise level at the most exposedwindow (or part of the roof) of abuilding, and to assume this exposure forother elements too. This may be suitableat the early design stage for large schools.However, where external noise levels varysignificantly, this approach can lead toover-specification and unnecessary cost.

3.8 CalculationsA calculation of the internal noise levelaccording to BS EN 12354-3:2000 canbe used to estimate whether, for the levelsof external noise at any particular site, aproposed construction will achieve thelevels in Table 1.1. By estimating theinternal levels for various differentconstructions, designers can determinethe most suitable construction in anygiven situation. BS EN 12354-3:2000allows the effect of both direct andflanking transmission to be calculated, butin many cases it is reasonable to consideronly direct transmission.

3.9 Test methodField testing of an existing buildingenvelope should be conducted accordingto BS EN ISO 140-5:1998[10], withreference to the clarifications given in thissection.

BS EN ISO 140-5:1998 sets outvarious test methods. The three ‘global’tests using the prevailing external noisesource(s) (road traffic, railway traffic, airtraffic) are preferable. At most sites roadtraffic is likely to be the dominant sourceof noise, and the correspondingstandardised level difference is denotedDtr,2m,nT . Where aircraft noise is themajor concern measurements should bemade accordingly, and the standardisedlevel difference denoted Dat,2m,nT .Similarly the standardised level differenceusing railway noise as the source isdenoted Drt,2m,nT .

The global loudspeaker test method(which generates Dls,2m,nT values) may

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be used only if the prevailing externalnoise sources are insufficient to generatean adequate internal level.

It is reasonable, under certainconditions as specified below, to use thetest results to indicate the likelyperformance of building envelopes of asimilar construction, exposed to similarsources. If the conditions are not metthen it is not reasonable to infer theperformance from existing soundinsulation test results and the calculationprocedure should be used.

3.9.1 Conditions for similarconstructionsThe following features of any untestedconstruction should be similar to those ofthe tested construction:• type and number of ventilators • glazing specification, frame

construction and area of windows• type and number of doors• external wall construction and area• roof construction and area.

3.9.2 Conditions for similar sourcesOnly test results in terms of Dtr,2m,nT ,Dat,2m,nT , Drt,2m,nT and Dls,2m,nTvalues are applicable, and these shouldnot be used interchangeably. Thefollowing features concerning theprevailing sources of noise should besimilar to those of the previously testedconstruction:• relative contributions of road traffic,

railway and aircraft noise• orientation of the building relative to

the main noise source(s)• ground height of the building relative

to the main noise source(s)

SOUND INSULATION BETWEENROOMS

This section describes constructionscapable of achieving the different levels ofsound insulation specified in Tables 1.2and 1.4.

Appendix 1 describes how soundinsulation between adjacent rooms ismeasured and calculated.

In addition to the transmission ofdirect sound through the wall or floor,additional sound is transmitted into the

Figure 3.4: Soundtransmission pathsbetween adjacent rooms:direct sound paths throughthe wall and floor andflanking paths through thesurrounding ceiling, walland floor junctions

airborne sound

impact sound

receiving room via indirect, or 'flanking'paths, see Figure 3.4.

3.10 Specification of the airbornesound insulation between rooms using RwTable 1.2 describes the minimumweighted sound level difference betweenrooms in terms of DnT (Tmf,max),w.However, manufacturers provideinformation for individual buildingelements based on laboratory airbornesound insulation data measured accordingto BS EN ISO 140-3:1995[5], in terms ofthe sound reduction index, Rw. Figure3.5 shows the values of Rw for sometypical building elements.

This section provides some basicguidance for the designer on how to uselaboratory Rw values to choose a suitableseparating wall or floor for the initialdesign. However, specialist advice shouldalways be sought from an acousticconsultant early on in the design stage toassess whether the combination of theseparating and flanking walls is likely toachieve the performance standard in Table1.2. An acoustic consultant can useadvanced methods of calculation topredict the sound insulation (eg StatisticalEnergy Analysis or BS EN 12354-1:2000[11]). The correct specification offlanking walls and floors is of highimportance because incorrect specificationof flanking details can lead to reductions in

Sound insulation3

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the expected performance of up to 30 dB. The following procedure can be used

to choose an appropriate type ofseparating wall or floor before seekingspecialist advice on appropriate flankingdetails.

1. Determine from Table 1.2 therequired minimum weighted BB93standardised sound level differencebetween rooms, DnT(Tmf,max),w .

2. Estimate the required weighted soundreduction index for the separating wall orfloor.

a. Use the following formula to providean initial estimate of the measured sound reduction index (Rw,est) thatshould be achieved by the separating wallor floor in the laboratory.

Rw,est =

DnT(Tmf,max),w +10 lg ( ) +8 dB

where DnT(Tmf,max),w is the minimumweighted BB93 standardized leveldifference between rooms from Table 1.2.

S is the surface area of the separatingelement (m2)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s)V is the volume of the receiving room(m3).

b. Estimate the likely reduction in theairborne sound insulation that wouldoccur in the field, to account for lessfavourable mounting conditions andworkmanship than in the laboratory test.X can be estimated to be 5 dB assumingthat flanking walls and floors are specifiedwith the correct junction details.However, if flanking walls and floors arenot carefully designed then poor detailingcan cause the airborne sound insulation tobe reduced by up to 30 dB. To allow thedesigner to choose a suitable separatingwall for the initial design it isrecommended that X of 5 dB is assumedand an acoustic consultant is used tocheck the choice of separating elementand ensure that the correct flankingdetails are specified.

STmf,maxV

Figure 3.5: Typical soundinsulation figures forconstruction elements,dB Rw

60

55

50

45

40

35

30

25

20

15

10

5

01 10 20 50 100 200 400

Weight kg/m2

Aver

age

soun

d re

duct

ion

inde

x, d

B R

w

6 mmglass200 mmspace

6 mmglass10 mmspace

12 mmglass

25 mmwall board

6 mmglass

3 mmglass

Hollow corepanel door

Solid coretimber door

12 mmplasterboardwith50 x 100 studs

100 mm breezeunplastered

100 mm breezeplasteredone side 115 mm

brickworkplastered

115 mmconcrete slabwith 50 mmscreed

100 mm slabwith resilienthangers

100 mm slabwith rigidhangers

225 mmbrickworkplastered

150 mmstaggered studwith 12 mmplasterboard

100 mm breezeplasteredboth sides

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c. Calculate the final estimate for theweighted sound reduction index Rw thatshould be used to select the separatingwall or floor from laboratory test data:

Rw = Rw,est + X dB

3.10.1 Flanking detailsA simplified diagram indicating the mainflanking transmission paths is shown inFigure 3.6. General guidance on flankingdetails for both masonry and framedconstructions can be found in ApprovedDocument E. Specific guidance onflanking details for products can alsosometimes be found from manufacturers'data sheets, or by contactingmanufacturers’ technical advisers.

3.10.2 Examples of problematicflanking detailsIn some buildings it is considereddesirable to lay a floating screed (eg asand-cement screed laid upon a resilientmaterial) across an entire concrete floorand build lightweight partitions off thescreed to form the rooms, see Figure3.7(a). This allows the flexibility tochange the room spaces. However, acontinuous floating screed can transmit asignificant quantity of structure-borneflanking sound from one room toanother.

For example, if a lightweight partitionwith 54 dB Rw was built off a continuousfloating screed the actual sound insulationcould be as low as 40 dBDnT(Tmf,max),w. In fact, even if a moreexpensive partition with a higherperformance of 64 dB Rw was built, theactual sound insulation would still be 40dB DnT(Tmf,max),w, because the majorityof sound is being transmitted via thescreed, which is the dominant flankingpath. This demonstrates the importanceof detailing the junction between thescreed and the lightweight partition. Toreduce the flanking transmission, thefloating screed should stop at thelightweight partition, see Figure 3.7(b).

Another flanking detail that can causeproblems is where a lightweight profiledmetal roof deck runs across the top of aseparating partition wall. With profilessuch as trapezoidal sections, it is very

difficult for builders to ensure that theydo not leave air paths between the top ofthe partition wall and the roof.

3.10.3 Junctions between ceilings andinternal wallsCeilings should be designed in relation tointernal walls to achieve the requiredcombined performance in respect ofsound insulation, fire compartmentationand support.

In the case of suspended ceiling systems

Through the junctionwith the external walls

Through the junctionwith the internal walls

Through the junctionwith the ceiling andfloor slab above

Through the junctionwith the floor slab below

Figure 3.6: The four mainflanking transmission paths

Figure 3.7: (a) Flanking transmissionvia floating screed (b) Corrective detailing

(a) (b)

the preferred relationship is one in whichpartitions or walls pass through thesuspended ceiling membrane, do notrequire support from the ceiling system,and combine with the structural soffitabove to provide fire resistingcompartmentation and sound insulation.

The alternative relationship in whichpartitions or walls terminate at, or justabove the soffit of a suspended ceiling, isnot recommended as it demands a ceilingperformance in respect of fire resistanceand sound insulation which is difficult toachieve and maintain in practice in schoolbuildings. This is because the number offittings required at ceiling level isincompatible with testing of fire resistanceto BS 476 Fire tests on Buildings andStructures [12], which is based on a testspecimen area of ceilings without fittings.Furthermore, the scale and frequency ofaccess to engineering services in theceiling void through the membrane (inrespect of fire) and through insulationbacking the membrane (in respect ofsound) is incompatible with maintenanceof these aspects of performance.

3.11 Specification of the impactsound insulation between rooms using Ln,wTable 1.4 describes the minimum impactsound insulation between rooms in termsof L′nT(Tmf,max),w. However,manufacturers usually provide informationfor floors based on laboratory impactsound insulation data measured accordingto BS EN ISO 140-6:1998[13], in termsof Ln,w.

This section provides some basicguidance for the designer on how to uselaboratory Ln,w values to design a suitableseparating floor. However, specialistadvice should always be sought from anacoustic consultant early on in the designprocess to assess whether the combinationof the separating floor and flanking wallsis likely to achieve the performancestandard in Table 1.4. An acousticconsultant can use advanced methods ofcalculation to predict the sound insulation(eg, Statistical Energy Analysis or BS EN12354-2:2000[14]).

The following procedure can be used

to choose an appropriate type ofseparating floor before seeking specialistadvice on flanking details from anacoustic consultant.

1. Determine the maximum weightedBB93 standardised impact sound pressurelevel, L′nT(Tmf,max),w from Table 1.4.

2. Estimate the required weightednormalised impact sound pressure levelfor the separating floor, as follows:

a. Use the following formula to providean initial estimate of the weightednormalised impact sound pressure level(Ln,w,est) that should be achieved by theseparating floor in the laboratory:

Ln,w,est =

L′nT(Tmf,max),w + 10 lg –18 dB

where L′nT(Tmf,max),w is the maximumweighted BB93 standardised impactsound pressure level from Table 1.4 V is the volume of the receiving room(m3)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s).

b. Estimate the likely increase in theimpact sound pressure level that wouldoccur in the field (ie, account forfavourable mounting conditions and goodworkmanship in the laboratory test), X.

X can be 5 dB assuming that flankingwalls are specified with the correctjunction details. However, if flankingwalls are not carefully designed the impactsound pressure level can increase by up to10 dB. To allow the designer to choose asuitable separating floor for the initialdesign it is suggested that an X of 5 dB isassumed and an acoustic consultant isused to check the choice of separatingfloor and ensure that the correct flankingdetails are specified.

c. Calculate the final estimate for theweighted normalised impact soundpressure level Ln,w that should be used toselect the separating wall or floor fromlaboratory test data.

Ln,w = Ln,w,est – X dB

10

Sound insulation3

VTmf,max

3.12 Internal walls and partitions

3.12.1 General principlesFigure 3.5 shows typical values of thesound reduction index (Rw) for differentwall constructions. For comparison theperformance of other constructionsincluding doors, glazing and floors isincluded.

The solid line shows the theoreticalvalue based purely on the mass law. Forsingle leaf elements (eg walls, singleglazing, doors, etc) the mass law statesthat doubling the mass of the elementwill give an increase of 5 to 6 dB in Rw .When constructions provide less soundinsulation than predicted by the mass lawit is usually because they are not airtight.

In general, lightweight double-leafconstructions such as double glazing,cavity masonry or double-leafplasterboard partitions provide bettersound insulation than the mass law wouldindicate. At medium and highfrequencies, double-leaf constructionsbenefit from the separation of the two

leaves, with performance increasing withthe width of the air gap between theleaves and the physical separation of theleaves. (Note that for double-leafplasterboard constructions, timberstudwork is rarely used to achieve highstandards of sound insulation becauselightweight metal studs provide bettermechanical isolation between the leaves.)

At low frequencies the performance ofplasterboard partitions is limited by themass and stiffness of the partition.Therefore, masonry walls can providebetter low frequency sound insulationsimply because of their mass. This is notobvious from the Rw figures, as the Rwrating system lends more importance toinsulation at medium and highfrequencies rather than low frequencies.This is not normally a problem in generalclassroom applications where soundinsulation is mainly required at speechfrequencies. However, it can be importantin music rooms and in other cases wherelow frequency sound insulation isimportant.

11

3Sound insulation

Figure 3.8: Chart forestimating transmissionloss (TL) for a compositewall consisting of 2elements of differingtransmission losses

15.0

14.0

13.0

12.0

11.0

10.0

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.02 6 10 14 18 22 26 30

Corr

ectio

n, d

B

Transmission loss difference, dB

5%

10%

20%

30%

40%

50%

60%

Area

The percentage of the total area of the wall occupiedby the element with the lower transmission loss, eg adoor, and the difference between the higher TL andthe lower TL, are used to calculate the correction indB which is added to the lower TL to give the TL ofthe whole wall.

For example: Assume a classroom to corridor wall hasan Rw of 45 dB and a door in the wall has an Rw of 30dB. If the area of the door is 0.85 m x 2.1 m =1.785 m2 and the area of the wall is 7 m x 2.7 m =18.9 m2, then the percentage of the wall occupied bythe door is 1.785/18.9 x 100 = 9.4%

The difference in TLs = 15 dB.

Therefore reading from the chart gives a correction ofabout 9 dB to be added to the lower TL, giving acomposite TL of 39 dB.

If a higher performance door of say 35 dB had beenused, the composite TL would be 35 + 7 = 42 dB.

A combination of masonry and dry-lining can be very effective in providingreasonable low frequency performancelinked with high sound insulation athigher frequencies. This combination isoften useful when increasing the soundinsulation of existing masonry walls.

While partition walls may be providedas a means of achieving sound reduction,it should be remembered that soundinsulation is no better than that providedby the weakest element.

Figure 3.8 can be used to assess theoverall effect of a composite constructionsuch as a partition with a window, door,hole or gap in it. The sound insulation ofthe composite structure is obtained byrelating the areas and sound insulationvalues of the component parts using thegraph.

Partitions should be well sealed, assmall gaps, holes, etc. significantly reducesound insulation. (Note that this appliesto porous materials, eg porous blockwork,which can transmit a significant amountof sound energy through the pores.)

3.12.2 Sound insulation of commonconstructions Figure 3.9 shows the approximateweighted sound reduction index Rw formasonry and plasterboard constructions.

Using the procedures given in Section3.10, it is possible to determine whichconstructions are capable of meeting therequirements between different types ofrooms.

The values in Figure 3.9 are necessarilyapproximate and will depend on theprecise constructions and materials used.Many blockwork and plasterboardmanufacturers provide data for specificconstructions. When using manufacturers’data it should always be ascertained thatthe data is tested to the standards given inSection 1, and details of the preciseconstruction used should be sought. Forexample, in masonry constructions, thethickness and density of plaster andrendering have a significant effect.

Some more specific sound reductionindices, both single value and octave banddata, and further references to specificmanufacturers’ data are in the sound

reduction indices spreadsheet included onthe DfES websitewww.teachernet.gov.uk/acoustics.

3.12.3 Flanking transmission In general, a weighted sound leveldifference of up to 50 dB Dw can beachieved between adjacent rooms by asingle partition wall using one of theconstructions described above, providedthat there are no doors, windows or otherweaknesses in that partition wall, andflanking walls/floors with their junctiondetails are carefully designed. Flankingtransmission is critical in determining theactual performance and specialist adviceshould be sought from an acousticconsultant.

3.12.4 High performanceconstructions – flanking transmissionHigh-performance plasterboard partitionsor masonry walls with independent liningscan provide airborne sound insulation ashigh as 70 dB Rw in the laboratory.However, to achieve high performance inpractice (ie above 50 dB Dw), flankingwalls/floors with their junction detailsmust be carefully designed. Airbornesound insulation as high as 65 dB Dw canbe achieved on site using highperformance plasterboard partitions, ormasonry walls with independent liningswith lightweight isolated floors andindependent ceilings to control flankingtransmission. This will require specialistadvice from an acoustic consultant.

For rooms which would otherwiseneed high-performance partitions it maybe possible to use circulation spaces,stores and other less noise-sensitive roomsto act as buffer zones between roomssuch that partitions with lower levels ofsound insulation can be used. Case Study7.4 (see also Figure 2.4) describes apurpose built music suite which usesbuffer zones effectively. In some cases,such as the refurbishment of musicfacilities in existing buildings, roomlayout may not allow this, and in thesecases high levels of sound insulationbetween adjacent rooms will be required.

12

Sound insulation3

13

3Sound insulation

Performance Rw Walls - typical forms of construction

1x12.5 mm plasterboard each side of a metal stud (total width 75 mm)

75 mm block (low density 52 kg/m2) plastered/rendered 12 mm one side

40–45 1x12.5 mm plasterboard each side of a 48 mm metal stud with glass fibre/mineral wool in cavity (total width 75 mm)

100 mm block (low density 70 kg/m2) fair faced

45–50 2x12.5 mm plasterboard each side of a 70 mm metal stud (total width 122 mm)

112 mm fair faced brick (unplastered)

100 mm block (medium density 140 kg/m2) plastered/rendered 12 mm both sides

50–55 2x12.5 mm plasterboard each side of a 150 mm metal stud with glass fibre/mineral wool in cavity (total width 198 mm)

224 mm fair faced brick (unplastered)

150 mm block (high density 315 kg/m2) plastered/rendered 12 mm both sides

55–60 2x12.5 mm plasterboard each side of a staggered 60 mm metal stud with glass fibre/mineral wool in cavity (total width 178 mm)

336 mm fair faced brick (unplastered)

Figure 3.9: Walls - soundreduction index for sometypical wall constructions

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Sound insulation3

Performance Rw (+/– 3 dB) Glazing - typical forms of construction

25 4 mm single float (sealed)

28 6 mm single float (sealed)

4/12/4: 4 mm glass/12 mm air gap/4 mm glass

30 6/12/6: 6 mm glass/12 mm air gap/6 mm glass

10 mm single float (sealed)

33 12 mm single float (sealed)

8/12/16: 8 mm glass/12 mm air gap/16 mm glass

35 10 mm laminated single float (sealed)

4/12/10: 4 mm glass/12 mm air gap/10 mm glass

38 6/12/10: 6 mm glass/12 mm air gap/10 mm glass

12 mm laminated single float (sealed)

40 10/12/6 lam: 10 mm glass/12 mm air gap/6 mm laminated glass

19 mm laminated single float (sealed)

10/50/6: 10 mm glass/50 mm air gap/6 mm glass

43 10/100/6: 10 mm glass/100 mm air gap/6 mm glass

12 lam/12/10: 12 mm laminated glass/12 mm air gap/10 mm glass

45 6 lam/200/10: 6 mm laminated glass/200 mm air gap/10 mm + absorptive reveals

17 lam/12/10: 17 mm laminated glass/12 mm air gap/10 mm glass

Figure 3.10: Glazing - sound reduction index for some typical glazing constructions

3.12.5 Corridor walls and doorsThe Rw values in Table 1.3 should beused to specify wall (including anyglazing) and door constructions betweencorridors or stairwells and other spaces.To ensure that the door achieves itspotential in terms of its airborne soundinsulation, it must have good perimetersealing, including the threshold wherepractical.

Note that a lightweight fire door willusually give lower sound insulation than aheavier, sealed acoustic door.

Greatly improved sound insulation willbe obtained by having a lobby doorarrangement between corridors orstairwells and other spaces. However, thisis not often practicable between classroomsand corridors. Some noise transmissionfrom corridors into classrooms isinevitable, but this may not be importantif all lesson changes occur simultaneously.

For some types of room, such as musicrooms, studios and halls for music anddrama performance, lobby doors shouldgenerally be used.

3.13 Internal doors, glazing, windowsand folding partitions Internal doors, glazing and windows arenormally the weakest part of anyseparating wall. Figures 3.10 and 3.11show the performance of a number ofdifferent types of door and window. Ingeneral, rooms which require at least 35dB Dw should not have doors or singleglazing in the separating wall or partition.

3.13.1 DoorsThe choice of appropriate doors withgood door seals is critical to maintainingeffective sound reduction, and controllingthe transfer of sound between spaces.

Internal doors are often of lightweighthollow core construction, providing onlyaround 15 dB Rw which is about 30 dBless than for a typical masonry wall (seeFigure 3.5). The sound insulation of anexisting door can be improved byincreasing its mass (eg by adding twolayers of 9 mm plywood or steel facings)as long as the frame and hinges cansupport the additional weight. However,it is often simpler to fit a new door.

The mass of a door is not the onlyvariable that ensures good soundinsulation. Good sealing around the frameis crucial. Air gaps should be minimisedby providing continuous grounds to theframe which are fully sealed to themasonry opening. There should be agenerous frame rebate and a proper edgeseal all around the door leaf. Acousticseals can eliminate gaps between the doorand the door frame to ensure that thedoor achieves its potential in terms of itsairborne sound insulation.

As a rule of thumb, even a goodquality acoustically sealed door in a 55 dBRw wall between two classrooms willreduce the Rw of the wall so that theDnT(Tmf,max),w is only 30-35 dB. Twosuch doors, separated by a door lobby, arenecessary to maintain the soundinsulation of the wall. Figure 3.12 showsthe effect of different doors on the overallsound insulation of different types of wall.In a conventional layout with access toclassrooms from a corridor, the corridoracts as a lobby between the two classroomdoors.

3.13.2 LobbiesSome more specific sound reductionindices, both single value and octave banddata, and further references to specificmanufacturers’ data are in the soundreduction indices spreadsheet included onthe DfES websitewww.teachernet.gov.uk/acoustics. Thegreater the distance between the doors,the better the sound insulation,particularly at low frequencies. Maximumbenefit from a lobby is associated withoffset door openings as shown in Figure 3.13(a) and acoustically absorbentwall and/or ceiling finishes.

A lobby is useful between aperformance space and a busy entrancehall. Where limitations of space preclude alobby, a double door in a single wall willbe more effective than a single door; thisconfiguration is illustrated in Figure3.13(b).

Inter-connecting doors between twomusic spaces should be avoided and alobby used to provide the necessaryairborne sound insulation.

15

3Sound insulation

Sound insulation3

16

Acoustic performance Typical construction

30 dB Rw This acoustic performance can be achieved by a well fitted solid core doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop. A 30 minute fire doorset (FD30) can be suitable.

Timber FD30 doors often have particle cores or laminated softwood cores with a mass per unit area ≈ 27 kg/m2 and a thickness of ≈ 44 mm.

Frames for FD30 doors often have a 90 mm x 40 mmsection with a stop of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this acoustic performance.

35 dB Rw This acoustic performance can be achieved by specialist doorsets although it can also be achieved by a well fitted FD60 fire doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop.

Timber FD60 doors often have particle core or laminated softwood cores with a mass per unit area ≈ 29 kg/m2 and a thickness of ≈ 54 mm. Using a core material with greater density than particle or laminated softwood can result in a door thickness of ≈ 44 mm.

Frames for FD60 doors can have a 90 mm x 40 mm section with stops of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this performance.

Figure 3.11: Doors -sound reduction index forsome typical doorconstrutions

44 mm

54 mm

44 mm thick timber door, half hour fire rated

54 mm thick timber door, one hour fire rated

NOTES ON FIGURE 3.11

1. Care should be taken to ensure that the force required to open doors used in schools is notexcessive for children. To minimise opening forces, doors should be fitted correctly and goodquality hinges and latches used. Door closers should be selected with care.2. The opening force at the handles of doors used by children aged 5–12 should not exceed 45 N.3. Manufacturers should be asked to provide test data to enable the specification of door-sets.4. Gaps between door frames and the walls in which they are fixed should be ≤ 10 mm.5. Gaps between door frames and the walls in which they are fixed should be filled to the fulldepth of the wall with ram-packed mineral wool and sealed on both sides of the wall with a non-hardening sealant.6. Seals on doors should be regularly inspected and replaced when worn.

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3.13.3 Folding walls and operablepartitions

Folding walls and operable partitionsare sometimes used to provide flexibilityin teaching spaces or to divide open planareas. A standard folding partition withno acoustic seals or detailing may providea value as low as 25 dB Rw . However,folding partitions of very high acousticquality are available; these can provide upto 55 dB Rw but as well as being costlythese are very heavy (typically 55-65kg/m2) and, unless electrically operated,are time-consuming to open and close.The sound insulation depends on effectiveacoustic sealing and deteriorates if seals ortracks are worn or damaged.

Folding partitions are useful in manyapplications but they should only be usedwhen necessary and not as a response to anon-specific desire for flexibility in layoutof teaching areas.

3.13.4 Roller shuttersRoller shutters are sometimes used toseparate kitchens from multi-purposespaces used for dining. Because rollershutters typically only provide sound

insulation of around 20 dB Rw it iscommon for noise from the kitchen todisturb the teaching activities. Onesolution is to provide doors in front ofthe shutters to improve the soundinsulation.

(a)

(b)

Figure 3.13: Use oflobbies and double doors(a) Lobbied doorway(b) Double door

Figure 3.12: Reductionof sound insulation of awall incorporating differenttypes of door1 For mean soundinsulation values for variouspartition/doorcombinations refer toFigure 3.8.2 Values in examples givenare for illustative purposesonly, ie, they are notabsolute.

20

50

40

30

30 40 50

Double doors, ie, one door either sideof a lobby (the diagonal straight line illustrates how the insulation value ofthe original partition can only bemaintained at 100% by incorporating aset of double doors with a lobby)

Heavy door with edge seal

Light door with edge seal

Any door (gaps round edges)

Sound insulation of wallwithout door (dB)

Sound insulation of wall 1 with door (dB)

1

'very good'

'good'

'poor'

eg 100 mm: stud work with plasterboardand skin both sides (no insulation)

eg 300 kg/m 150 mm 'high' densityblockwork, plastered at least one side

eg 225 mm common brick plasteredboth sides

2

2

Sound insulation3

18

Figure 3.14: Existing timber floors - sound reduction index for some typical floor/ceiling constructions

1

2

3

4

5

6

7

Basic timber floor consisting of 15 mm floorboardson 150-200 mm wooden joists, plaster orplasterboard ceiling fixed to joists

As 1, ceiling consisting of one layer of 15 mmplasterboard and one layer of 12.5 mm denseplasterboard fixed to proprietary resilient bars onunderside of joists

As 1, ceiling retained, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 240 mm cavity containing 80-100 mm lightweightmineral wool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 275 mm cavity containing 80-100 mm lightweightmineral wool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedspecial resilient hangers to give 275 mm cavitycontaining 80-100 mm lightweight mineral wool(>10 kg/m3)

As 1 with proprietary lightweight floating floor usingresilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board supported on 45 mm softwood battens laid on 25 mm thickopen-cell foam pads). 80-100 mm lightweightmineral wool (>10 kg/m3) laid on top of existingfloorboards

As 1, floorboards removed and replaced with 15 mm tongue-and-groove floorboards on a 15 mmplywood, chipboard or fibre-bond board supportedon 12 mm softwood battens laid on 25 mm thickopen-cell foam pads bonded to the joists, 80-100 mm lighweight mineral wool (>10 kg/m3)laid on top of existing ceiling

35–40 80–85 180–230

50–55 65–70 220–270

55–60 60–65 450–500

55–60 60–65 450–500

60–65 55–60 450–500

50–55 60–65 270–320

55–60 55–60 240– 290

Option Construction - timber floors Rw Lnw depthmm

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19

multi-storey buildings with woodenfloors, such as traditional Victorian schoolbuildings. Both airborne noise and impactnoise can be problematic with woodenfloors, and both problems need to beconsidered when dealing with verticallyadjacent spaces. Adding carpets or othersoft coverings to wooden floors reducesimpact noise but has very little effect onairborne noise.

Impact noise can also be a problemwith concrete floors (although airbornenoise may not be a problem); this cansometimes be solved by adding a carpet.

3.14 Floors and ceilingsSound transmission between verticallyadjacent rooms occurs through:• airborne noise where the sound poweris input into the room and is transmittedthrough the separating floor and itsassociated flanking constructions.• impact noise where the structuralpower is input into the floor (eg throughfootfalls, chairs scraping, etc) and istransmitted through the separating floorand its associated flanking constructions.

Vertical noise transmission betweenclassrooms can be a problem in older

8

9

10

11

As 7 but mineral wool replaced by 100 mmpugging of mass 80 kg/m2 on lining laid on top ofceiling

As 8 but with 75 mm pugging laid on top of boardfixed to sides of joists

As 1 with proprietary lightweight floating floorusing a continuous layer (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 6-12 mm thickcontinuous open-cell foam mat)

As 10, ceiling removed and replaced withsuspended ceiling consisting of 2 layers of 15 mmwallboard or 2 layers of 12.5 mm denseplasterboard, suspended on a proprietary metalceiling system to give 275 mm cavity containing80-100 mm lightweight mineral wool (>10 kg/m3)

55–60 50–55 240– 290

50–55 55–60 240– 290

50–55 55–60 220– 270

60–65 50–55 360– 410

NOTES ON FIGURE 3.141. Where resilient floor materials are used, the material must be selected to provide thenecessary sound insulation under the full range of loadings likely to be encountered in that roomand must not become over-compressed, break down or suffer from long-term ‘creep’ under thehigher loads likely to be encountered. Where large ranges of loading are encountered, or wherethere are high point loads such as pianos, heavy furniture or operable partitions, the pad stiffnessmay have to be varied across the floor to take account of these.2. All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Figure 3.14 Continued

Option Construction - timber floors Rw Lnw depthmm

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20

Figure 3.15: Lightweightconcrete floors - soundreduction index of sometypical constructions

1

2

3

4

5

6

7

Lightweight floor consisting of concrete planks(solid or hollow) or beam and blocks, with 30-50mm screed, overall weight approximately 100 kg/m2, no ceiling or floor covering

As 1 with soft floor covering >5 mm thick

As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm lightweight mineral wool(>10 kg/m3)

As 3 with soft floor covering >5 mm thick

As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)

As 1 with proprietary lightweight floating floorusing a continuous layer (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 6-12 mm thickcontinuous open-cell foam mat)

As 1 with heavyweight proprietary suspendedsound insulating ceiling tile system

35–40 90–95 100–150

35–40 75–85 105–155

60–65 55–60 370–420

60–65 50–55 375–425

50–60 50–60 155–205

50–55 55–60 150–200

45–55 60–70 250– 500

Option Construction - lightweight concrete floors Rw Lnw depthmm

3.14.1 Impact sound insulationImpact noise on floors may arise from:• foot traffic, particularly in corridors atbreak times/lesson changeover• percussion rooms• areas for dance or movement• loading/unloading areas (eg in kitchens and workshops) • machinery.

In general, impact noise should bereduced at source through use of softfloor coverings or floating floors.

Planning and room layout can be usedto avoid impact noise sources on floorsabove noise-sensitive rooms. Soft floorcoverings and floating floor constructionsand independent ceilings are the mosteffective means of isolation, and resilient

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Figure 3.16: Heavyweightconcrete floors - soundreduction index of sometypical constructions

1

2

3

4

5

Solid concrete floor consisting of reinforcedconcrete with or without shuttering, concretebeams with infill blocks and screed, hollow orsolid concrete planks with screed, of thicknessand density to give a total mass of at least 365kg/m2, with soft floor covering >5 mm thick

As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)

As 1 with proprietary lightweight floating floorusing a continuous layer (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 6-12 mm thickcontinuous open-cell foam mat)

As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm lightweight mineral wool(>10 kg/m3)

As 4 with soft floor covering >5 mm thick

50–55 60–65 150–200

55–60 50–55 200–250

55–60 50–60 175–230

60–70 55–60 420–470

60–70 50–55 425–475

NOTES ON FIGURES 3.15 AND 3.161. Where "soft floor covering" is referred to this should be either a resilient material, or materialwith a resilient base, with an overall uncompressed thickness of at least 4.5 mm ; or any floorcovering with a weighted reduction in impact sound pressure level of not less than 17 dB whenmeasured in accordance with BS EN ISO 140-8:1998[15] and calculated in accordance with BSEN ISO 717-2:1997[16]. 2. Where resilient floor materials are used, the material must be selected to provide thenecessary sound insulation under the full range of loadings likely to be encountered in that roomand must not become over-compressed, break down or suffer from long-term ‘creep’ under thehigher loads likely to be encountered. Where large ranges of loading are encountered, or wherethere are high point loads such as pianos, heavy furniture or operable partitions, the pad stiffnessmay have to be varied across the floor to take account of these.3. All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Option Construction - heavyweight concrete floors Rw Lnw depthmm

Sound insulation3

22

floor finishes are also appropriate forsome sources.

Typical airborne and impact noiseperformance are listed for a number ofconstructions in Figures 3.14, 3.15 and3.16. Note that, unlike airborne soundinsulation, impact sound insulation ismeasured in terms of an absolute soundlevel, so that a lower figure indicates abetter standard of insulation. (SeeAppendix 1 for a more detailed explanationof airborne and impact sound insulation.)

3.14.2 Voids above suspendedceilingsWhere partitions run up to the undersideof lightweight suspended ceilings, theairborne sound insulation will be limitedby flanking transmission across the ceilingvoid, which will often prevent theminimum values for airborne soundinsulation in Table 1.2 being achieved.Therefore, partitions should either becontinued through the ceiling up to thesoffit, or a plenum barrier should be used.

3.14.3 Upgrading existing woodenfloors using suspended plasterboardceilingsFigure 3.14 shows the airborne andimpact noise performance of a standardwooden floor with various forms ofsuspended plasterboard ceiling.

Option 2 is possibly the most widelyused system of increasing both impactand airborne sound insulation, with orwithout the original plaster ceiling. Insmall rooms good results can be achievedusing timber studs fixed only to the walls,but large timber sections are needed tospan wider rooms.

In wider span rooms it is generallymore convenient to suspend theplasterboard from the floor joists above,fixing through the existing ceiling if this isretained, using a proprietary suspensionand grid system (option 4). The grid canbe hung from simple metal strips or, forhigher performance, special flexibleceiling hangers.

The major manufacturers of dry-liningsystems all provide their own systems forthese options, and provide soundinsulation data and specifications for a

variety of configurations. The performancefor both airborne and impact soundimproves with the depth of the ceilingvoid, with the mass of the ceiling andwith the deflection of the ceiling hangersunder the mass of the ceiling. Adding alayer of lightweight acoustically absorbentglass wool or mineral wool in the ceilingvoid increases the sound insulation,typically by 2-3 dB, but there is no pointin adding more than specified.

Performance on site is stronglydependent on good workmanship toavoid air gaps, so careful attention shouldbe given to ensuring that joints are close-butted, taped and filled and that all gapsare properly sealed. At the perimeter asmall gap should be left between theplasterboard and the walls, and thisshould be sealed using non-setting masticto allow a small amount of movementwithout cracking.

Penetrations through the ceiling needto be properly detailed to maintain anairtight seal while allowing movement,and services should not be allowed toprovide a rigid link between the ceilingand the floor above. This can be aparticular problem with sprinkler pipes. Aproblem with these constructions is thatrecessed light fittings, grilles and diffuserssignificantly reduce the sound insulationso any services should be surface-mounted.

The plasterboard finish is acousticallyreflective whereas in some rooms anacoustically absorbent ceiling is required,to meet the specifications for roomacoustics and reverberation times. Onesolution to this, if there is sufficientheight, is to suspend a separatelightweight sound absorbing ceiling underthe sound insulating plasterboard ceiling.This can be a standard lightweightcomposite or perforated metal tile system.These lightweight, acoustically absorbent,ceilings add very little to the soundinsulation but do provide acousticabsorption. Lights and services can berecessed in the absorbent ceiling.

The term ‘acoustic ceiling’ generallyrefers to lightweight acousticallyabsorbent ceiling tile systems, designed toprovide acoustic absorption. Note that

3Sound insulation

23

these systems do not always increase thesound insulation as well.

There are, however, some systemswhich use relatively heavy ceiling tileswhich are designed to fit into ceiling gridsto provide a reasonably airtight fit. Thesemay consist of dense plasterboard ormineral fibre products, or perforatedmetal tiles with metal or plasterboardbacking plates. If properly installed andmaintained these can provide a usefulincrease in sound insulation as well asacoustic absorption. Manufacturers ofthese systems can provide both airborneand impact sound insulation figures, aswell as acoustic absorption coefficients. Ifno measured sound insulation data areprovided, it is better to err on the side ofcaution and assume that the tile will notprovide a significant increase in soundinsulation.

The sound insulation performancefigures quoted in Figure 3.14 all assumethat the floorboards are in goodcondition and reasonably airtight, withthin carpet laid on top. If retaining theoriginal floorboards it is good practice tofill in any gaps with glued wooden strips,caulking or mastic, or to lay hardboard ontop, to provide an airtight seal. If notretaining the original boards, 18 mmtongue-and-grooved chipboard can beused to achieve the same effect, with alljoints and gaps properly sealed, especiallyat the perimeters.

3.14.4 Upgrading existing woodenfloors using platform and ribbed floorsThe systems discussed in Section 3.14.3all maintain the original wooden floormounted directly on joists. This has theadvantage of maintaining the originalfloor level at the expense of loss of ceilingheight below. An alternative approach isto provide a floating floor system eitheron top of the existing floorboards (aplatform floor) or to remove the existingfloorboards and build a new floor onresilient material placed on top of thefloor joists (a ribbed floor). In both casesthe increase in both airborne and soundinsulation relies on the mechanicalisolation of the floor from the joists usingresilient material.

Figure 3.14 shows a number of typicallightweight floating floor constructionsand indicative sound insulation figures.There are many proprietary systems usinga wide range of isolating materials andmanufacturers should supply test data inaccordance with ISO 140 measurements.

The isolating layer will typically consistof rubber, neoprene, open-cell or closed-cell foams, mineral fibre or compositematerials. The isolating layer can be in theform of individual pads, strips or acontinuous layer of material.

The sound insulation increases with thedeflection of the resilient layer (up to thelimit of elasticity for the material), withthe mass of the floating layer and with thedepth of the cavity. Adding a layer oflightweight acoustically absorbent glasswool or mineral wool in the ceiling voidincreases the sound insulation, typically by2-3 dB, but there is no point in addingmore than specified. In each case thedeflection of the material under thepermanent ‘dead’ load of the floatinglayer and the varying ‘live’ loads ofoccupants and furniture must beconsidered. If the material is too resilientand the floating layer is insufficientlyheavy or rigid, the floor will deflect underthe varying loads as people move aboutthe room. For this reason it isadvantageous for the floating layer to beas heavy and as stiff as practicable, insome cases using ply or fibre-bond board(for mass) laid on top of the resilientlayer, with tongue-and-grooved chipboardon top of this.

If there are likely to be very heavy localloads in the room (eg pianos) it may benecessary to increase the stiffness of theresilient material, or, in the case of pads,to space the pads more closely together tosupport these loads.

Junctions with walls and at doors needto be designed to maintain an effectivelyairtight seal while allowing movement ofthe floating layer. Manufacturers generallyprovide their own proprietary solutionsfor this, with or without skirtings.

Lightweight floating floors are quitespecialist constructions, and achieving thecorrect deflection under varying live loadswithout overloading the resilient material

24

Sound insulation3

can be difficult. Most materials sufferfrom long term loss of elasticity or ‘creep’under permanent loads and this should betaken into account in the design andselection of materials. The systemmanufacturer should normally beprovided with all of the relevantinformation and required to specify asystem to meet all of the acoustic andstructural requirements over the expectedlifetime of the floor. In difficult cases theadvice of an acoustics consultant and/orstructural engineer should be sought.

3.14.5 Concrete floorsIn general concrete floors provide muchgreater airborne sound insulation thanwooden floors by virtue of their greatermass. There are, however, considerablevariations in performance between densepoured concrete floors and comparativelylightweight precast concrete plank floors.Impact sound transmission can be aproblem even in heavy concrete floorsbecause of the lack of damping inconcrete, and a soft or resilient floorcovering is generally required. This maysimply be carpet on suitable underlay.

Figures 3.15 and 3.16 show typicalairborne sound insulation and impactsound transmission for a number oftypical concrete floor constructions, with

and without suspended ceilings andfloating floors.

3.15 Design and detailing ofbuilding elementsImportant points to remember whendesigning constructions to achieveadequate sound insulation are: • Weak elements (eg doors and glazing,service penetrations, etc) will reduce theeffectiveness of the walls in which they arelocated.• Impact sound will travel with littlereduction through a continuous membersuch as a steel beam or servicing pipe.• Partitions between sensitive spacesshould normally continue beyond theceiling up to the structural soffit or rooflayer, to prevent noise passing over thetop of the partition above the ceiling orthrough a loft space.• Openings in walls caused by essentialservices passing through should beacoustically sealed. Pipework passingbetween noise sensitive spaces should beappropriately boxed-in (see ApprovedDocument E[1]).

Figure 3.17 shows how possibletransmission paths through the structureof a building can be prevented.

allconnectionsfor plant andmachineryshould be flexible

walls must be ofadequate weightand all gaps sealed

airborne sound transmited through ceiling,light fittings, and lightweight partitions and gaps

can be dealt with by sealing gaps and increasing mass

impact sound and to a lesser degree,airborne sound, can be transmitted along the structure

all gaps forducts and pipes

in walls and floorshould be well sealed

airborne sound transmittedthrough ductwork

ceiling below plant may needto be isolated from floorabove and from ductwork assuspended ceiling can bea good amplifier forstructure borne noisecreated by badly isolatedplant

plantroomshould haveflexiblemountings,adequatefloor massand elasticity,or floatingfloor

partitions should normally extendup to the soffitFigure 3.17: Possible

sound transmission pathsand their prevention

25

3Sound insulation

References[1] Approved Document E - Resistance to thepassage of sound. Published by the StationeryOffice, 2002 ISBN 001 753 6433

[2] Sound Control for Homes (BRE report 238,CIRIA report 127 available from CRC Ltd), BRE & CIRIA, 1993BRE ISBN 0 85125 559 0CIRIA ISBN 0 86017 362 3CIRIA ISBN 0305 408 X

[3] J. McLoughlin, D.J. Saunders, R.D. Ford.Noise generated by simulated rainfall onprofiled steel roof structures. Applied Acoustics42 (1994) 239-255

[4] ISO 140-18 Acoustics Measurement ofsound insulation in buildings and of buildingelements - Part 18: Laboratory measurementof sound generated by rainfall on buildingelements, forthcoming standard.

[5] BS EN ISO 140-3: 1995 Measurement ofsound insulation in buildings and of building elements. Part 3. Laboratory measurement ofairborne sound insulation of building elements.

[6] The Education (School Premises)Regulations 1999. (Statutory Instrument 1999No 2, EDUCATION, ENGLAND & WALES ). TheStationery Offiice, 1999. ISBN 0 11 080331 0£3.00 and on websitewww.legislation.hmso.gov.uk/si/si1999/19990002.htm

[7] BS EN 20140-10: 1992 Acoustics,Measurement of sound insulation in buildingsand of building elements. Part 10. Laboratorymeasurement of airborne sound insulation ofsmall building elements.

[8] BS 98/704582 DC. Ventilation forbuildings. Performance testing ofcomponents/products forresidential ventilation. Part 1. Externally andinternally mounted air transfer devices. Draftfor Public Comment (prEN 13141-1 CurrentEuronorm under approval).

[9] BS EN 12354-3:2000 Building Acoustics -Estimation of acoustic performance in buildingsfrom the performance of elements. Part 3.Airborne sound insulation against outdoorsound.

[10] BS EN ISO 140-5: 1998 Measurement ofsound insulation in buildings and of building elements. Part 5. Field measurements ofairborne sound insulation of façade elementsand facades.

[11] BS EN 12354–1:2000 Building Acoustics.Estimating of acoustic performance in buildingfrom the performance of elements. Part 1.Airborne sound insulation between rooms.

[12] BS 476 Fire tests on building materialsand structures.

[13] BS EN ISO 140-6: 1998, Acoustics -Measurement of sound insulation in buildingsand of building elements. Part 6. Laboratorymeasurement of impact sound insulation offloors.

[14] BS EN 12354-2: 2000 Building Acoustics.Estimating of acoustic performance in buildingfrom the performance of elements. Part 2.Impact sound insulation between rooms.

[15] BS EN ISO 140-8: 1998 Acoustics.Measurements of sound insulation in buildingsand of building elements. Part 8. Laboratorymeasurements of the reduction of transmittedimpact noise by floor coverings on aheavyweight standard floor.

[16] BS EN ISO 717-2: 1997 Acoustics - Ratingof sound insulation in buildings and of buildingelements. Part 2. Impact sound insulation.