Almost 20 years after a devastating World in Action exposé, the timber frame industry is back under the microscope. This time,government-backed research has found that poor workmanship is exposing occupants of timber frame buildings to potentially fatal fire risks. Thomas Lane and Andy Pearson report

FIREALARM

Date 1997Type of property Timber frame terraced houseWorkmanship issue A fire occurred in the cavityof a timber-framed building, due to a nakedflame being introduced through a tumble dryerventilation hose attached through a hole to theoutside wall. There was no separation betweenthe premises on fire and the adjoining house. If this fire had gone unchecked it could havespread to the adjoining house.

Date 2000Type of property Timber frame terraced houseWorkmanship issue Fire started when a workmaninstalling a shower cut through plasterboard andapplied a blowtorch into the wall cavity to solderpipes. A fire-stopping plasterboard wall collapsedduring the fire, contributing to the fire spreadingto adjacent properties. Home improvements hadweakened this wall.

Date 2000Type of property Brick-and-block terraced houseWorkmanship issue A small fire burned througha plastic air-brick into a cavity wall of brick-and-block construction. The fire then spread throughthe insulation in the cavity wall. It started inhouse number 41, and spread to 43. Smoke from the fire also spread to numbers 39 and 45.This is because there appeared to be inadequatefire-stopping between the houses. Fire crews cutholes in the brickwork of houses 41 and 43 tocontain and extinguish the fire. The terrace wasabout a year old.

Date 2001Type of property Timber frame semi-detachedhouseWorkmanship issue Fire penetrated thebuilding’s brick outer skin through a small holefor the TV and telephone cable. The fire ignitedplywood cladding in the wall space. It thenspread upward inside the walls.

Date 2001Type of property Flats converted fromcommercial premisesWorkmanship issue A fire was started by theoccupant leaving cooking unattended. Excessivesmoke and fire penetration occurred to the flat

above. A section of the wall and ceiling had tobe cut away to gain access to extinguish the fire. On investigation it was found there wasinadequate fire-stopping in the cavity where ithad been breached by the installation of anextractor fan duct.

Date 2002Type of property Terraced houseWorkmanship issue A builder solderingpipework ignited cavity wall insulation. Fire spread upwards along the cavity toneighbouring properties’ roof spaces and floor timbers. Lack of fire separation assisted fire spread.

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SHODDY WORKMANSHIP IS LEAVING TIMBERframe buildings exposed to heightened risk of fire, potentially endangering the lives ofthousands of people.

The risk to homes, nurses’ homes, old people’shomes and student flats was revealed at a privateseminar last week organised by the DTI andindustry researchers. The experts who gathered atBRE’s headquarters in Watford have uncoveredalarming evidence that badly installedplasterboard drylining and fire protectionmeasures mean a fire can spread uncontrolledthrough cavity walls.

And the problem may affect more than justtimber frame buildings. Mark Van Scalwyck, aninsurance inspector for Zurich Municipal, says:“Most of the defects we find relate to cavityconstruction. About one in four properties haveproblems with fire stopping.” However, timberframe buildings are most at risk because theircavities are lined with combustible materials.

These revelations are a potential disaster for an

industry that took years to recover from a Worldin Action exposé in 1983. The programme showedexamples of poor site practice on timber framehousing sites and listed 30 types of recurrentdefects. Recently, however, it seemed that thishad all been forgotten: the government has beenpromoting timber frame construction because ofits environmental credentials and also because it

uses factory-made wall frames and roof trusses –useful given the shortage of skilled siteoperatives. Last year, the industry turned over£247m and produced more than 23,000 units.

Mostyn Bullock, principal engineer at researchbody Chiltern International Fire, says: “There isanother World in Action programme waiting tohappen. What if one of these student blocks wentup and people died? These places are deathtraps.”

While the occupants of the buildings are clearlyin most danger, there are potential financial risksfor owners. Insurers are warning that they mayrefuse to pay for fire damage where poorworkmanship has allowed a blaze to spread. Theymay also demand that only approved timberframe contractors are used. Industry experts havein turn responded to the development by callingfor building control officers, or other independentconsultants, to sign off the correct installation offire stops in cavities.

These workmanship problems are compoundedby fears that fires can reignite in the cavity of E

Examples of fires in cavities from the London Fire & Emergency Planning Authority database

What if one of thesestudent blocks wentup and people died?These places aredeathtrapsMostyn Bullock, Chiltern International Fire

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E a timber frame building because the timberssmoulder undetected for hours. Oxfordshire FireBrigade has changed its procedures so that fireofficers must return to the scene of a timberframe building blaze after four hours, to checkthe fire has not reignited in the cavity. For othertypes of construction, this is at the discretion ofthe fire fighters.

The fears of fire experts like Bullock were firstaroused on 15 September 2000, when BREcarried out a test on a specially constructed, six-storey, timber frame building in an old airshiphangar at its Cardington Research Centre.

A fire was deliberately started in the living roomof one of the second-floor flats in the south-westcorner of the block. The fire spread through theflat and raged for an hour before the fire brigadeput it out. But two-and-a-half hours later, afterthe fire fighters had left, smoke was seen comingout through joints in the external brickwork. Itseemed the fire had reignited in the wall cavity.

The fire brigade was called back, and

immediately evacuated the building. They foundthe heat of the fire was causing the brickwork tocrack, and decided to fight the fire from theoutside. However, because the fire was in thecavity, they were unable to locate its source andwere pointing their hoses wherever they sawsmoke coming from the building. In order toreach the cavity, fire fighters took out some ofthe window frames and removed the eaves

protection; they even had to resort to taking outsections of the brickwork.

The blaze was eventually extinguished five-and-a-half hours after the fire brigade was recalled.The destruction was extensive. When the firereignited in the cavity, it caused severe damage tothree flats above the one in which the fire started.

So what went wrong? Fire investigators revealedat the seminar that after the initial fire wasthought to have been extinguished, a section ofthe timber frame in the cavity smoulderedundetected for an hour-and-a-half beforebursting into flames. The fire then ripped throughthe wall cavity to the three flats above. Thesesuffered extensive damage because the fire-protection measures, which should have stoppedthe blaze spreading, were ineffective. Thehorizontal cavity closers had become dislodged bymortar dropping on them during the constructionof the wall and some were actually missing.

Even more alarmingly, this discovery was thesecond example of how poor workmanship is

The only reason thesefires have not receivedwider publicity is that nobody has been killed yetSenior building control officer

Cavity barrier at junctionwith party floor

Where the cavity barriers are located: a multistorey residential building

Cavity barrier at junction ofparty wall and external wall

Cavity barrier aroundwindow opening

Brickwork outer skin

Ventilated cavity

Insulation

Internal lining

Timber sheathing

Cavity barrier at junctionwith party floor

Timber stud

exacerbating the fire risk to timber framebuildings. The first emerged before the test waseven carried out. Plasterboard in the test flat had to be taken out and reinstalled. “The linings were not put up properly and the jointsweren’t staggered,” said Bullock. If the originalplasterboard had remained, he added, “wewouldn’t have got 60 minutes [fire resistence], itwould have been more like 20”. This is becausethe fire could have breached the plasterboarddrylining and broken into the cavity.

The results of the Cardington test raised fearsthat the risks of fire spreading through wallcavities in timber frame buildings could be muchmore extensive. Timber frame is thought to bemore vulnerable than masonry constructionsbecause the cavity is lined with combustiblematerials (see diagram, left). It is not an intrinsicfault in the design, but it does mean theworkmanship has to be accurate in order for afire to be localised.

A spokesperson for the Timber IndustryResearch Association said the solution wastraining, education and policing: “The industryneeds to police itself or the Building Regulationsneed to include third-party certification.” In astatement to Building, the UK Timber FrameAssociation said: “UKTFA recognises that poorworkmanship in the installation of cavity barriersfor fire protection is a problem throughout theconstruction industry. Where barriers are missing,not installed correctly or not properly overlapped,there is an increased risk of fire occurring. This isan industry-wide problem and not specific totimber frame.”

Following the Cardington test in 2000, thegovernment launched a research project headed“Understanding Fire Risks in CombustibleCavities”. The project is being carried out by BREand Chiltern Fire under a DTI-sponsored Partnersin Innovation programme. Their report is due tobe published in September.

In an attempt to gauge the scale of theproblem, the researchers commissioned BRE’s fireand risk sciences division to study cavity fires. Thedivision looked at a 20% sample of all fires thathave occurred over the past five years. The studyrevealed most cavity fires occurred in timberframed buildings, with domestic dwellings thehighest risk group. It also highlights theconsiderable amount of damage caused both as a result of the fire and of the fire brigadedestroying walls to get to the seat of the blaze.

Last week’s seminar was organised to determinethe extent of the problem in the industry and togain anecdotal evidence from those attendingthe seminar. It is now apparent that shoddyworkmanship is a serious concern that will behighlighted in September’s report.

As part of the project, the researchers alsovisited three sites where timber frame was being used – a social housing project and twoprivate developments. To their horror, they foundthe cavity closers in each were installedincorrectly. In some instances, they were pulledtight round corners exposing gaps, and in othersbricklayers were ripping them out when they gotin the way.

“The brickies find cavity barriers get in the way and remove them,” says James Lavender, a

Chiltern fire engineer. “They also think you don’tneed them if the cavity is small.”

The researchers believe that timber framehomes are at most risk. Fires in domesticbuildings have been caused by faulty electricalwiring in wall cavities, and even the heatgenerated by drilling holes in a wall to install asatellite dish, which could lead the timber frameto start smouldering. One senior building controlofficer told Building: “The only reason these fireshave not received wider publicity is that nobodyhas been killed yet.”

Another part of the investigation has focusedon the conditions under which fire reignites in acavity. The researchers set up a test in which afire was started in a cavity through a hole in the brickwork. The fire was allowed to burnthrough the timber cavity lining before beingextinguished. But the fire carried on smouldering,and after an hour-and-a-half it had charredthree sets of structural timber studs. After threehours, the timber burst into flames. “We thoughtit had all died down,” says Lavender, “It reignitedin a matter of seconds without us noticing.”

The researchers also tested the cavity closersthemselves to prove that they do in fact stop firespreading. This was found to be the case whenthe closers are correctly installed, but when a gapof two or three fingers’ width is left, and it ispulled tight round a corner, the fire reachedtemperatures of 250°C above the closers afterjust two minutes. Flames also burst through theclosers and reached sections of the timber frameabove. Lavender points out this suggested that insuch instances, the building would be in breachof Part B of the Building Regulations, whichcovers fire safety.

The publication of the research report inSeptember is likely to presage widespreadchanges in the way timber frame buildings are constructed and regulated, although agovernment spokesperson emphasised that “the issues [in the report] are relevant to allconstruction types”. Apart from the threats frominsurers, there may be calls for the design oftimber frame cavity walls to be changed to makethem less vulnerable to the spread of fire. Thiscould include changing their construction tokeep flammable material out of the cavity, andcavity closers may have to be redesigned to makethem easier to install correctly. But this crisis isn’t primarily about design – it’s yet anotherconstruction disaster. And for the proponents oftimber frame, it has terrible echoes of thatcataclysmic moment nearly 20 years ago whenWorld in Action’s cameras rolled.

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Where the industry is going wrong

Plasterboard fixingn The wrong types of fixings are often usedn Fixings are sometimes incorrectly spacedn The lower layer of plasterboard can beincorrectly fixed – boards attached with only theminimum of fixingsn Plasterboard joints are not staggered and thelower layer of boards have large gaps betweenn Plasterboard noggins are incorrectly fixed,wrongly located or missing

Timber frame issuesn Even though the components of many timberframe constructions are fabricated in the factory,there are still problems with the correctinstallation and fixing of componentsn Key structural elements are missing fromconstructionsn Galvanized steel fixings are used to securestainless steel componentsn Open perpends are not installed above cavitybarriers and apertures

Breather membranen Incorrect installation and fixing of membrane,which results in it becoming ripped or edges notoverlapping correctly

Wall tiesn Installed at the wrong angle to allow drips to fall n Installed with incorrect fixingn Ties missing

Cavity Barriersn Not installed during constructionn Incorrectly installed, creating gaps between thebarriersn Barriers knocked out of place by falling mortarinside the cavity, creating gaps between barriers

Source: Partners in Innovation report number O-CIF001:Reinstatement of Fire Damaged Timber Frame Buildings

What the industry is doing to change

n Increasing the use of prefabricated units withprefitted cavity barriersn Introducing a UKAS-accredited quality schemeas a requirement of UKTFA membership.n Developing erector training and accreditationto national standards n Looking at the introduction of new sheathingmethods and materials n Looking at how the fire brigade pinpointssources of fire