Thatched Property Safety Guide

Produced by your local Fire and Rescue Service

© 2017 Design produced in-house by Hertfordshire Fire and Rescue Service’s Graphics Department

The Fire Service acknowledges the kind permission of John Albion Duffield & Pratt to use their publications in the production of this guide.

Photographs courtesy of Hertfordshire, Cambridgeshire and Norfolk Fire and Rescue Service’s.

Illustration page 9 reproduced from MyGARD plc leaflet.

The information contained in this document is alsoavailable upon request in large print and in communitylanguages. Please contact your Local Fire and RescueService stating the format you require.

Contents Introduction

Causes

Precautions

Safety devices

Advice and Information

Checklist

Useful contact information

ChimneysFire planSmoke alarmsKitchensElectricsDon’t overload sockets!ContractorsBonfiresWater suppliesHeat sensorsSprinkler systems

Summary of advice

Spark arrestorsHeat detectorsThe Dorset modelTar removersStovepipe monitors

Open fires and wood burnersChimney firesFaulty chimneysSeasoned woodHeight of chimney

What is Heat Transfer?

4

8

11

16

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Introduction

2

Thatchedroofing isenjoying arevival in theUK.Roofing was traditionallymade from severalmaterials depending onlocation and availability.

Today, however, only threematerials are widely used,long straw, combed wheatreed and water reed, all ofwhich will burn rapidly in afire.

This booklet has beenproduced by your local Fireand Rescue Service as auseful guide for householders to help prevent afire occurring.

This booklet should be keptclose at hand and passedon to the new occupiershould you move.

Although fires in a thatchroof are not common, over90% start as a result of afaulty flue or chimney.

The thatch is designed torepel water and so for aFire and Rescue Servicethis makes it a difficult taskto extinguish such fires.

“prevention is essential,detection is nearly alwaystoo late!”

Recent research hasidentified that a major causeof chimney related thatchfires is attributable to heattransfer through thebrickwork of the flue into theadjacent thatch. Thegovernment-backed team ofscientists from the NationalSociety of Master Thatchers(NSMT) have conductedresearch into the use ofstraw and reed as a roofingmaterial. In particular theirresearch included aninvestigation into the causesof preventable thatch fires.

It was believed that themajor cause of thatch fireswas attributed to sparks orburning brands issuing fromthe chimney and igniting thethatch. In fact, controlledtests have shown that it isdifficult to ignite thatch withsuch a short-lived point ofignition as a spark. It is

particularly difficult to ignitewhen the thatch is cold andwet; as is invariably thecase when homeowners arelighting fires that sendsparks up the chimney.

Their experiments haveshown that the temperatureof the flue gases inside thechimney will heat thesurrounding brickwork. The‘hot bricks’ of the chimneywill heat the adjacent thatcharound the chimney. Thatchis an extremely goodinsulator and the heat willbe retained in the centre ofthe thatch around thechimney. The experimentsshowed that once a criticaltemperature of approx200°C was achieved at thethatch chimney interface,charring and pyrolysis of thethatch occurred andeventually developed into aroof fire. This processdevelops over long periodsof time.

Causes

3

What is Heat Transfer?

Many thatched homes werebuilt with single skin brickchimneys that rise centrallythrough a deep thatch layer.They were designed tocater for open fireplaces,often smoking inglenooks,where large volumes ofcooling air drawn fromdraughty rooms mingledwith the flue gases as theyrose through the flue.Diluted in this way, the fluegases did not reachsufficiently hightemperatures to pose athreat to the thatch adjacentto the chimney. As thechimney traditionallyemerged through thehighest point of the thatch,any partly combustedparticles were expelledupwards and wereextinguished before theydrifted down towards thethatch.

Modern enclosed solid fuelappliances are designed toburn efficiently and cleanly.This means that they burnat a much-increasedtemperature to promote a‘clean burn’. Solid fuelstoves can generate fluegas temperatures in excessof 300°C to 600°C. Whenthese appliances are fittedinto elderly chimneys andthere is only a 4-inch layerof brick between the flueand the thatch, then thethatch is especiallyvulnerable to the risk ofheat transfer. Modernchimney linings can preventflue leaks, but they do notsignificantly reduce thetemperature achieved byheat transfer within thethatch when the applianceis in constant or regularuse.

Precautions

4

Open fires and wood burners

It has been shown in teststhat the thatch adjacent tothe chimney can reach 85%of the flue gas temperatureafter only one day ofcontinuous use. The criticaltemperature of 200°C canbe achieved and sustainedwith relative ease.

Precautions

5

Chimney fires can occur inany home with a workingflue, including homes thathave conventional tile orslate roof. It should beremembered that soot isnot merely a by-product ofburning; it is a combustiblematerial in its own right. Asoot-lined chimney is achimney lined with fuel justwaiting to burn. Onceignited, the draught withinthe chimney can draw thefire into something akin to ajet engine exhaust. Thisextremely fiercecombustion is capable ofreaching such hightemperatures that thestructure or the chimney

can be significantlydamaged. In a thatchedhome the conventionalchimney fire carries theadditional risk of igniting theroofing material.

Old or poorly maintainedchimneys can deteriorate tothe point where smoke andhot gases can escape fromthe chimney into the upperrooms, the roof space ordirectly into the thatch.There are several tell talesigns that indicate problemswith the chimney. Any

Chimney fires

Faulty chimneys

Precautions

6

Chimneys built before the1960’s, and this is true ofmost thatched homes, aremost likely of a single brickthickness and parged, notlined. The internal protectiveparging or roughcastplasterwork will crumble anddisintegrate with age,leaving the brickwork orstonework of the chimneyexposed to the acidiccondensate that isgenerated by modernappliances. The chemicalreactions that subsequentlyoccur accelerate the attackon the mortar and furtherdeterioration can be rapid.

Because of the great age of

many thatched homes, theconstruction of thechimneys can be highlyunconventional. Periodhomes, built before BuildingRegulations wereintroduced, often havetimber lintels over thefireplace and timber joistsbuilt into the chimneystacks. These can beexposed to scorching whenthe protective parging insidethe chimney disintegrates.

The combustion productsfrom burning sap in‘green’ wood are the maincause of tar depositswithin a chimney.Whenwood is properly seasonedthe sap content issubstantially reduced andso is the tar.Apart from minimising thebuild up of tar, there is alsoa significant financial benefitof burning properlyseasoned wood. With itslower sap content it gives offmore heat and offers bettervalue for money.

Any staining of theplasterwork or wallpaperaround the chimneybreast,or black or brown localiseddeposits on the chimney inthe roof space should betaken seriously. Soot oncobwebs in the loft isanother vital sign thatsomething is wrong with thechimney.

Seasoned wood

Precautions

7

Irrespective of how dry theshed or garage is, storingwood inside will result in‘sweating’. Any sap, whichis drawn to the cut surfaceof the wood, will condenseon the surface as opposedto being taken away.Stacking it outside where itis exposed to the wind andsun properly seasonsWood. The wood shouldeither be stored under ashelter or the top layershould be covered toprotect the stack againstexcessive rain.

A chimney with only alittle part of the stackvisible, is likely to beburied in deep thatch,raising the chimney stackdoes not reduce the riskof fire. Old properties canhave thatch at the eaves upto 10ft deep, making this aproperty at risk. One metreor more of thatch round achimney is a potentialhazard, at the time of re-

thatching work with thethatcher and theconservation officer to haverecent layers of thatchremoved to reduce the risk.

Height of chimney

Safety devices

8

In the past, acceptedwisdom largely dictatedthat a major cause of firesin thatched homes wasattributed to sparksissuing from the chimneyand igniting the thatch. Asa consequence, manyowners of thatched homeswere persuaded to installspark arrestors on workingchimney pots. Although wedo NOT recommend sparkarrestors on chimneys, ifthey are installed they mustbe kept clean.

In a recent survey by theteam of scientists fromNSMT, it was found that ofall the thatched propertiesinvestigated, which hadsuffered chimney relatedfires, many had some typeof restrictor on the roof.This was often a cloggedspark arrestor.

If a spark arrestor is fittedor is going to be fitted itmust be kept clean to allow

it and the chimney to workefficiently. The NationalAssociation of ChimneySweeps recommend that ifa spark ‘arrestor’ is fitted toa chimney in regular use,the chimney should beswept every 3 months andthe spark arrestor takendown and thoroughlycleaned.

There are systemsavailable, which use heatdetectors inserted intothe thatch around thechimney connected to acontrol panel. The systemis designed to give anaudible warning when thebrickwork and thatcharound the chimneyapproaches a criticaltemperature. Installationcosts and an annualmaintenance program needto be considered, togetherwith a risk managementstrategy to be adoptedwhen an alarm is given.

Spark arrestors

Heat detectors

9

The system is designed togive an early warning of a potential overheating of thethatch so measures can betaken to reduce thetemperature of the chimneyi.e. extinguish the fire in thegrate and inspect thechimney.

Working in closeassociation with the fireservice, thatcher’s,builders electricians,insurers, scientists andbuilding control divisionsthroughout the county ofDorset have grappled inrecent years with the localplanning demands fornew thatched propertiesto be built. As a result adesign guide has been

drawn up called the ‘Dorsetmodel’, which meets thecriteria of all the specialistadvisers appointed to thetechnical committee. Byfollowing this design guide itis possible to build a newhouse with a thatched roof.Some of the principles inthe Dorset model could beconsidered if any majorrenovation work of re-roofing is planned.Consideration could begiven to:

burning wood, when hot fluegases condense in the coolerparts of the chimney. As thecoolest region is theuppermost section of theflue, ignition of the tar at thispoint represents a seriousthreat to the thatch.

There are chemical productsavailable that can be appliedt

Constructing a fireproofbarrier between the rooftimbers and the thatchlayer. The thatch would then be viewed as‘sacrificial’ in the event offire and the fireproofbarrier would help stop the roof fire from gettinginto the structure of thehouse. This wouldtherefore drasticallyreduce the effect of athatch roof fire.

Insulating the flue of thechimney to reduce therisk of heat transfer.

Safety devices

The Dorset model

Safety devices

10

The build up of tardeposits within the fluecan increase the risk of achimney fire. Tar depositsare encouraged to form,particularly when burningwood, when hot flue gasescondense in the coolerparts of the chimney. As thecoolest region is theuppermost section of theflue, ignition of the tar atthis point represents aserious threat to the thatch.

There are chemicalproducts available that canbe applied to the embers ofthe hearth fire or firebox ina stove to dry out the tardeposits in the flue andcause them to disintegrate.This treatment should berepeated at therecommended intervals toprevent new deposits fromforming. Routine sweepingand scraping of the flue willstill be required, especiallywhere heavy tar depositspersist. A qualified chimney

sweep will be able to giveyou further adviceregarding the best productsto suit your particularrequirements.

Careful management ofany solid fuel or wood-burning appliance is aneffective way of reducingthe risk of heat transferfrom the chimney to thethatch. Using stovepipethermometers to monitorthe temperature of the fluegases leaving the appliancegives a good indication ofhow high the temperaturesin the upper part of thechimney will be. Thefirebox can be suitablymanaged to ensure thatthe flue gas temperatureis not excessive (approx200c) at the level of thethatch.

Stovepipe monitors

Tar removers

Advice and information

11

Chimneys should bechecked or surveyed toensure that they arestructurally sound, wellmaintained and able tocope with the demandsmade of them by modernheating appliances.

The first measure is toensure that the chimneysare regularly swept by anexperienced and preferablyqualified chimney sweep,who should be able toidentify potential problemsat an early stage.

If a chimney lining has beeninstalled, this should beinternally inspected atintervals, especially whenthe main fuel burnt is wood,as tar deposits are highlycombustible and corrosive.The majority of chimneylinings were not designedwith thatched homes inmind. Metal liners arevulnerable to corrosion anddo not have a long life

expectancy in associationwith wood burningappliances. CCTV can beused to inspect the internalcondition of the flue.Potential hazards can beidentified, diagnosed andremedies prescribed by aqualified chimney engineer.

One way of addressing therisk of heat transfer from theflue to the thatch is to usean insulated flue liner. Thereare a number of insulatedflue liners available on themarket. Metal liners areavailable with insulation oran infill can be used aroundthe liner. This infill is aninsulating material such as‘vermiculite’ or ‘pumice’.Clay liners can be used orthere are pre-formedcement modulesincorporating kiln burnt andpumice aggregate. Thesehave very good thermalqualities.

Whichever type of lining isconsidered, the chimney

Chimneys

should be scrupulouslycleaned prior to installation to remove combustibledeposits that mightotherwise ignite betweenthe lining and the flue. Acompetent chimneyengineer who understandsthe special risks associatedwith thatched propertiesshould install any linings.

Make sure all your familyknow what to do in theevent of a fire and how toescape safely. Your fireplan should include:

Your Fire Service stronglyrecommends smokealarms are installed in yourproperty.

Advice and information

12

Planning your escaperoutes and keepingexits clear.

Keeping door andwindow keys handy.

Considering how a firein your house will bedetected. Have you gota sufficient amount ofsmoke alarms and arethey in the correctposition?

Smoke alarms

Fire plan

13

Advice and information

Two-thirds of fires thatstart inside the houserelate to the kitchen.Consideration should begiven to:

Check for signs of loosewiring and faulty plugs orsockets, such as scorchmarks or flickering lights.

Installing a fire blanket.

Keeping items that cancatch fire easily, such astea towels and oven

gloves, away fromcookers and toasters.

Never fill a pan morethan one-third full of oil.

Consider a thermostatically controlled deep fat fryer.

As a CFS (Community Fire Safety) Department,we do NOT recommend fire extinguishers to beused in the kitchen. Afire blanket is safer and much more effective touse.

Electrics

Kitchens

Fit a smoke alarm on every floor of your home,ideally in the hallway orlanding ceilings.

Put a smoke alarm in theloft space and link this toothers inside the house.

Don’t put a smoke alarmin the kitchen where itcan be set offaccidentally.

Test the batteries once aweek. Alarms areavailable with 10-year batteries.

Advice and information

14

Consider having yourelectrical system checkedby a qualified electricianin accordance with theInstitution of ElectricalEngineers (lEE) guidance. If your incoming powersupply is overhead, check tosee if it is the insulated type.If you are in doubt yourpower supplier can give youfurther advice.

If you are having workdone on your house thatwill involve ‘hot works’such as plumbing or paintstripping, make sure thecontractors are fullyaware of the potential riskof a thatch fire.

It is always good practice tolimit the number andlocation of any bonfires toreduce the risk of fire toyour property. It is also agood idea to discuss thiswith any neighbours whohave a bonfire near yourproperty.

Assess the water suppliesto your property. Considerhaving an outside tap withenough hose pipe to reacharound your house includingthe roof. This will help youcontrol any small fires youdiscover. Only tackle a fire ifit is safe todo so.

Bonfires

Water supplies

Contractors

Don’t overload sockets!

Advice and information

15

There are systemsavailable, which use heatdetectors inserted into thethatch around thechimney connected to acontrol panel. They aredesigned to give an earlywarning if the thatch isoverheating. The fire inthe grate can then beextinguished to allow thechimney and the thatch tocool down.

In recent years there havebeen many advances indomestic sprinklersystems. The life safetyadvantages and the extraproperty protection can beconsiderable.

Sprinkler systems

Heat sensors

16

Checklist

Recent research hasshown the major cause of fires in thatchedproperties is heattransfer from thechimney into the thatch.The thatch then reachesits ignition temperatureand a roof fire candevelop. It is important toinsulate the chimney flueto prevent the heat fromtransferring into the thatchlayer. This is especiallyimportant when a solid fuel or woodburner is installed as they burn at highertemperatures thanconventional open fires.

Have the chimney sweptregularly by a qualifiedchimney sweep. Achimney in regular useshould be swept twice ayear.

Only burn seasonedwood.

Have the chimneyinspected by a qualifiedchimney engineer.

If you have a sparkarrestor fitted clean itregularly. This shouldbe done every 3 monthson chimneys in regularuse and the arrestorshould be taken downto clean.

Develop a fire plan foryour home.

Smoke alarms shouldbe installed throughoutyour home. If you have aloft space then aninterlinked smoke alarmshould be installed whichis linked to at least oneother within your home.

Summary of advice

Checklist

17

Install a fire blanket inthe kitchen.

Check the electricalsystem throughout yourhome.

Be careful when usingblowtorches or heatguns (when plumbing orpainting etc).

Restrict the use ofbonfires near to yourproperty.

Consider a system ofheat sensors within thethatch around thechimney. This will giveyou an early warning ofany overheating of thethatch.

Install an outside tapwith enough hose toreach around the houseincluding the roof. Thiscan be used to extinguishany fires at an earlystage.

Residential sprinklersystems will greatlyimprove the fireprecautions within yourhome. The advantageswill be much better lifesafety and propertyprotection.

If you are undertakingrenovation work or re-roofing, considerforming a fireproofbarrier between the rooftimbers and the thatchlayer. Any thatch fire willthen be mainly restrictedto the thatch and will notget into the structure ofthe house so greatlylimiting the damage fromfire.

Useful contacts...

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The contacts listed will giveyou specialist informationregarding their products.

See back cover for local Fire and Rescue Servicecontact details.

National Association of Chimney Sweeps www.nacs.org.uk

Local area Fire Prevention Officerswww.firekills.gov.uk

English Heritage - Listedbuildings/graded propertieswww.customers@english-heritage.org.uk

The National Society of Master Thatchers (NSMT)www.nsmtltd.co.uk

The East Anglian MasterThatchers Associationwww.eamta.co.uk

This ‘Thatched Property Safety Guide’ has been produced by your local Fire andRescue Service. It offers a variety of useful information and practical advice for bothyou and your home. We hope you find it informative and helpful.

For further information and advice see the ‘useful contacts’ section at the back ofthis booklet.

FREE SAFE & WELLCHECKS Contact your local Fire and Rescue Service to arrange yourappointment using the numbers below.

We will sit and work through a questionnaire with you answeringany questions you may have. We will then do a ‘walk around’inspection of your home with you, giving advice on potential firehazards that exist and where necessary we will also supply and fitsmoke alarms free of charge.

Visits will take place by mutual agreement and Fire and Rescuepersonnel will always show an official ID card.

It won’t cost you a penny and it could save your life.

SMOKE ALARMSThey’re not an EARLY warning. They’re your ONLY warning.

BEDFORDSHIRE 01234 845 000

CAMBRIDGESHIRE 0800 917 9994 (Freephone)

ESSEX 0300 303 0088

HERTFORDSHIRE 0300 123 4046

NORFOLK 0800 917 8137 (Freephone)

SUFFOLK 01473 588 888

Contact Your local Fire and Rescue Service...

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