The most popular building method for new social housing in the UK is a potential fire risk, government statistics have indicated, as fire safety experts warned that thousands of people could be living in unsafe blocks of flats.
According to a senior figure at one leading insurer, it could be "when, not if" a blaze in a block built using a central timber frame causes significant loss of life.
The experts point to a series of incidents where a relatively minor blaze in a flat has spread to the building's central core, often without residents or fire crews knowing until flames erupt elsewhere.
Timber-frame construction, in which a traditional-looking block is erected around a wooden skeleton, now accounts for 60% of all new social housing. Once reserved primarily for individual houses, the method – cheaper, faster to build and more environmentally friendly than masonry or steel and concrete – is now used for blocks of up to six or seven storeys.
The timber-frame industry insists its buildings are fully fire safe because combustible cavities are surrounded by fireproof walls. However, a number of fire brigades and fire experts say that while this method works in tests, too many timber-frame blocks are poorly constructed or else modified by residents. Even mounting a flat-screen TV without proper tools can punch holes in a fire-resistant internal wall, potentially allowing fire to spread into a common cavity, they say.
In one case in December investigators believe a major blaze at flats in Salford happened when a workman soldered a tiny exterior overflow pipe. Builders had neglected to fit fireproofing behind the pipe, allowing flames to spread. Residents were evacuated but the entire block had to be demolished at a cost of about £2m.
These worries are now backed by official data. Statistics released by the Department of Communities and Local Government (CLG) show fires in timber-frame dwellings have a greater average spread than those in traditionally built homes. While the number of blazes involved is relatively small, "the differences in proportions observed are unlikely to be the result of chance variation", statisticians conclude.
Jim Glockling, technical director of the Fire Protection Association, which investigates fire safety for insurers and others, said it was impossible to know how many buildings might be affected, but it could be significant. "Often these blocks are put up four at a time. When we investigate a fire and find a construction fault in one, can we assume the other three buildings are perfect? Possibly not. They might need a close look too."
The common advice that residents should stay in their homes if a fire breaks out elsewhere in the building, on the assumption that it will be contained, might need to be changed, he added: "If fires are going to behave in extraordinary ways then we need to start looking at evacuation procedures."
The statistics show no difference in death or injury rates. However, some believe that this could be largely a matter of good fortune. "At the moment we are mainly seeing disproportionate financial losses from fire in timber-frame buildings," a senior figure at a major insurance company said, asking not to be identified. "But the obvious worry is people being trapped if a fire spreads unexpectedly. It could be when, not if, we see a major tragedy."
Critics say the rapid expansion of the construction method has not been matched by improved knowledge among both contractors and residents. Plumbers and electricians need to use special tools to install services inside timber frame blocks, which is not always the case. Those living in the flats often don't even know how the building was built, as it is covered in brick, and make unsafe modifications, even as simple as installing extra electrical sockets in a fireproofing wall.
"There are dangers in a design if it assumes that the people who live in it are perfect," said Ian Cox, head of the Royal Berkshire Fire & Rescue Service and director of fire protection at the Chief Fire Officers' Association (CFOA). "With a building like this you need more active management to keep things safe. We are not against this type of building if it is done properly. But we think we need more testing."
Another concern is that it is often impossible even for firefighters to tell whether a building has a timber frame. Peter Holland, vice-president of the CFOA and Lancashire's chief fire officer, said: "It can be a real worry if you get to a fire and you don't know what you're going to be facing. You could think you're tackling a fire in a single room and then suddenly the roof is on fire."
The UK Timber Frame Association said it would examine the new statistics. "It's the first time we've been shown evidence like this and we will engage with the CLG over it," said its managing director, Joe Martoccia. "But it does involve a small number of fires, so we should be cautious [not to] read too much into it immediately."
The fire minister, Bob Neill, said: "We take fire safety very seriously and are aware of the questions raised about timber-framed buildings. The new government is listening to the public's concerns carefully and will tackle them head-on."
He added: "However, I also want to reassure people that on the whole we have a very good record in this country of making our buildings safe and reducing fire deaths."
Early warningIn September 1999, a government-commissioned test saw a six-storey timber-frame block of flats constructed at Cardington, near Bedford, before the living room of a third-floor apartment was deliberately set ablaze.
The results seemed impressive. While temperatures inside the flat soon reached 900C, when the fire was extinguished more than an hour later there was no sign of it having spread to other parts of the building. The firefighters and scientists went home.
But just before midnight, fire crews were called back after flames unexpectedly erupted again. Unknown to the testers, the fire had spread to a central timber cavity and then upwards.
It took firefighters five hours to bring the blaze under control. "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," Sam Webb, an architect and fire safety expert wrote in an article about the incident.
It was nonetheless declared a success. "The compartment fire test met the stated objectives of the programme," said the report. The company who led the experiment insists there was no cover-up; it was just that the test was considered to be over when the initial fire was put out.