Smouldering issue

Timber frame buildings
Despite extensive testing, timber frame buildings have never thoroughly shaken off suspicions of susceptibility to fire. Veteran building safety campaigner, architect Sam Webb, gives his personal view here, and opposite the BRE responds

In 1986 Margaret Thatcher abolished the GLC and the London Building Acts were repealed. Only allowed to keep their name, district surveyors were employed within the building control departments of the London Boroughs. Residual parts of the acts remained for Inner London Boroughs, like Section 20 of the 1939 Amendment Act.  The rest was consigned to the scrap heap, together with the independence of the emasculated district surveyors.

By 1986 the London Building Acts had been in force for 320 years, since Wren drafted the first Act of 1667 weeks after the Great Fire. The emphasis was on fire safety, its prevention and spread. No one wanted the city to burn down again. Wren’s ‘Rebuilding Act’ created London, while Section 20 allowed modern construction to the district surveyor and London Fire Brigade’s approval.

Each building designed under Wren’s Act, and those that followed, contained fire protection with party walls and masonry external walls. These limited fire by reducing radiation across the street, at the rear and between properties. Timber frame construction was effectively outlawed on safety grounds by insurers and the London Building Acts.

The National Building Regulations in 1991 led to problems which should have been foreseen by those in charge of the drafting. The new regulations allowed multi-storey timber framed flats in London and elsewhere for the first time.

Earlier this year, worried by a spate of fires in completed and partially completed multi-storey flats in London, the Greater London Assembly called an ‘Investigation into Fire Safety in Tall and Timber Framed Buildings in London’. It was held in City Hall on 16 March.

Its terms of reference stated that: ‘The assembly is mindful of the recent fire in Peckham, which is the latest major fire involving timber frame or tall building in London. The fires include the Colindale fire in 2006, during which a six-storey timber framed building burned to the ground in less than nine minutes.

‘In the light of these concerns, the assembly calls on the assembly planning and housing committee to set up a scrutiny investigation… and to make recommendations to the mayor of London with regards to the London Plan and to Her Majesty’s government with regard to building regulations.’

Assembly member Jenny Jones chaired the meeting. GLA members were there to question a panel of six: Ron Dobson, commissioner of the London Fire Brigade, Rita Dexter, assistant commissioner, Geoff Arnold, chairman of the UK Timber Frame Association, Paul Everall, chief executive of Local Authority Building Control, Richard Biggs of CIC and me.

Unknown to anyone in the room was what had happened to an Austrian timber frame block of flats a fortnight earlier. Certainly no-one said anything. A carelessly discarded cigarette dropped into a plastic bucket on a balcony had destroyed a three-storey apartment building in Salzburg in an hour on 2 March 2010. It was the latest major fire in a timber frame building. There was total loss with rebuilding costs estimated at ¤3m.

Arnold of the UKTFA was adamant that fire damage only ever occurred when buildings were under construction, never in a completed building. The Colindale fire, he suggested, was started by accelerant. Yet evidence shows that completed timber frame buildings are very vulnerable to fire, which often leads to total destruction of the building, people’s homes and all their belongings.

On Christmas Day 2007 a fully occupied four-storey timber framed block of flats in Croydon burned to the ground. One horrified resident told the BBC: ‘The windows in the block had been replaced with PVC. The previous windows had been made of wood. I saw fire enter my flat through the window space. The fire was dripping down through the window.’

The development of the fire was so rapid that the occupants lost everything. The original fire, caused by a boy playing with matches, was put out by the fire brigade and the block declared safe. Everyone moved back in and the boy’s family stayed with friends leaving someone to look after their flat. This person smelled smoke in the bedroom and found it pouring out of the junction between the windows and the wall. The second fire was inside the cavity and undetected by the first firemen.

Many councils have replaced original windows with plastic. Croydon is no exception. Over 90% of the windows in their blocks are uPVC. In London 15 out of 32 boroughs exclusively install uPVC windows and 212,000 council homes now have uPVC windows. That’s half the total stock.

In 2005 the BRE tested four types of window – hardwood, softwood, aluminium and uPVC – and their efficiency in preventing fire getting into a cavity. Without a timber fire stop closing the cavity above a uPVC frame, a fire took less than six minutes to enter the cavity at the head of the frame. A similar test with a softwood frame took 14 mins 45 secs.

The best results were where a timber fire stop was fitted yet in no case did any test exceed the 30 minutes requirement for a two-storey house before the fire entered the cavity. In timber frame construction that leads to disaster. It’s what happened in the Croydon fire which should have had 1 hour protection. It also happened in Salzburg and it has happened elsewhere in the UK and in Ireland.

In 1999 a fire in a fifth floor flat in Irvine, Scotland engulfed the upper nine floors. Within 10 minutes it had spread up seven floors of the traditionally built block via uPVC windows and GRP spandrels, killing a wheelchair-bound man. A parliamentary select committee recommended changes in fire regulations. That led to the Fire Safety Order 2005. They also issued a caveat: ‘We do not believe it should take a serious fire in which many people are killed before all reasonable steps are taken towards minimising the risks.’

The National Building Regulations of 1991 allowed timber frame flats for the first time up to 18m. Above this height the building requires 90 minutes fire protection, considered impossible in a timber frame. Provisions were simplified. Fewer cavity barriers were now needed in timber frame. The way was clear for timber frame to take off. Much was on its side: speed of erection, cleanliness, and, with timber coming from a renewable source, it was sustainable and green.

The speed at which timber frame took over the housing market and the construction of flats, not just in the UK but abroad, was astonishing. In a few years the market share increased 10 fold. But what it really needed was the seal of approval at the highest level. This came from the BRE.

On 15 September 1999, a full-scale fire test under the TF2000 programme was carried out at Cardington by the BRE on a six-storey timber framed block of flats. The fire brigade put out the fire after 64 minutes. Tests with thermal imaging devices failed to discover any hotspots. Considered a success by the BRE, timber frame was given a clean bill of health in the UK. A full report was produced by the BRE stating that: ‘The compartment fire test met the stated objectives of the programme.’

What is significant but not mentioned in the report was what then happened in the early hours of 16 September 1999 to this six-storey building, which the fire brigade had left and everyone considered safe. If it had been a real building people would have moved back in, played with their kids, read books, watched TV and gone to bed.

At 23.45 on 15 September fire alarms started to go off. These alerted the night staff. At 23.48 a 999 call was made to the Bedfordshire & Luton Fire Brigade. They arrived at 00.30. By 05.19 the fire was under control. The last appliance left at 15.20, nearly 16 hours after the second fire was first noticed. The fire started in a cavity in the structure on the third floor and spread with ‘abnormal rapid fire development – through cavities on floors 3,4,5 and 6’.

A number of unanswered questions arise from this. Why is there no mention of this second fire in the official report? What led the BRE to ignore this second fire as part of their test? The UKTFA appears to have known about this fire as reference is made to it on its website postings yet it says in another: ‘If you want to know how multi-storey timber frame buildings cope with severe fire, there is one key piece of research that you must read. The TF2000 project provided a six-storey experimental timber frame building for the sole purpose of investigating its structural and fire performance.’ UKTFA state that fires in cavity walls are rare and that: ‘Fire brigades have thermal imaging tools to help them locate the seat of a cavity fire very quickly after arriving at the scene’ (Timber Frame & Fire Safety).

That does not appear to be borne out by what happened and is certainly not what happened in Croydon. Is there anything else we have not been told?

BRE responds
Sam Webb makes a number of references to work carried out by BRE.  We believe it is important that some clarifications are provided to ensure that there is a clear understanding of the research work undertaken as part of the TF2000 project at Cardington and how the results from the project have been used to develop best practice guidance for the industry.

The first point relates to the reference to work carried out by BRE in 2005 entitled ‘Cavity Barriers: Final factual report of the experimental programme’. This research focussed on the time taken for fire to enter the timber frame cavity in ad hoc fire tests without any glazing in place. The times achieved in the ad hoc fire tests cannot be related directly to the 30 minute requirement in Approved Document B (AD B). For absolute clarity, the 30 minute requirement in AD B relates to the performance of elements of construction in a standardised fire resistance test. The results of the research have not been correlated with performance in a standardised fire resistance test as this was not within the scope of the project and therefore there is no robust technical basis for comparing the research results with the requirement. 

The article states that BRE provided the ‘seal of approval at the highest level’. The TF2000 project was a collaborative programme of research involving BRE, TRADA, industry and the UK government. The final report was produced by the project team in consultation with a large steering group representing a range of key stakeholders. The primary output from this project which is not referenced in the article is ‘Multi-storey timber-frame buildings – a design guide’ (BR 454). The publication of this design guide does not represent approval of multi-storey timber-frame constructions as each design and construction will be project specific and will be subject to scrutiny by the appropriate approvals authority. 

The article claims that as a consequence of the compartment fire test on the TF2000 building, ‘timber frame was given a clean bill of health in the UK’. This appears to be based on the BRE quote ‘The compartment fire test met the stated objectives of the programme’. The primary objective of the compartment fire test was to ‘evaluate the performance of a medium-rise six storey timber-frame building subject to a severe natural fire exposure’. Much of the information published in BR454 is a direct consequence of this evaluation. It points out that quality of workmanship is vital in relation to the success of fire safety provisions. It also makes clear that the correct location and installation of cavity barriers and fire stopping is important in maintaining the integrity of the structure wherever the material within the cavity provides a medium for fire spread. The quality of workmanship on site is important in ensuring the performance of many different construction products within any type of building. It is for this reason that BRE recommends the quality of workmanship and installation is subject to appropriate checks by a competent person and specifically, in relation to fire protection products, installation is carried out by an installer approved by an independent third party (such as LPCB – see www.redbooklive.com and LPS 1531 – Approved Installer of Passive Fire Protection Products).

Much of the rest of the article relates to the post-test fire spread where a small seat of combustion led to extensive fire spread within the cavity. It is claimed that BRE ignored this cavity fire incident. This is very far from the truth. The post-test fire incident was fully reported to the project partners and ultimately led to a collaborative research project ‘Understanding fire risks in combustible cavities’ awarded to Chiltern International Fire with BRE as partner. BRE acted impartially and accurately reported events that took place. The results from this project informed the guidance in BR454.

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