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In 2000 BRE set fire to an apartment inside a six-storey timber-framed building built inside a giant aircraft hangar. This was part of a government-funded project to see how multistorey timber-framed buildings performed in fires, structurally, and how this building type could be efficiently constructed. What is widely known is that the fire compartment performed as predicted – the fire brigade extinguished it in an hour. What wasn’t revealed is that the fire brigade had to be called back two and a half hours later because the fire had spread into the cavity, breaking out in the apartments above. It transpired the plasterboard lining hadn’t been installed properly and the barriers that should have stopped the fire spreading inside the cavity were missing. At the time nothing was done to ensure this wouldn’t happen on all those real multistorey timber-frame buildings that have been built since the test.

We are reaping the legacy of this neglect today.

While everyone has been focusing on the dramatic fires breaking out on half-built multistorey timber-framed jobs, insurers have been getting increasingly concerned about the rising cost of claims associated with completed, large buildings constructed using modern methods. If a fire gets into a cavity with flammable material present, it is very difficult to put out – in some cases demolition is the only answer, which results in disproportionate losses.

Timber frame is in the spotlight because of its inherent flammability. It has become a victim of its own success – there are a lot of large timber-framed buildings out there. Structural insulated panels are also a cause for concern, as is lightweight steel frame. The latter contains flammable material and in a fire, the heat can cause the frame to buckle.

In an attempt to tie down the numbers, RISCAuthority, a research and lobbying body for the insurance industry, has launched a database which includes the building type and construction method of buildings affected by fire. The first set of data reveals that 40% of the losses over £150,000 occurred in buildings constructed using modern methods of construction (MMC). Although RISCAuthority cautions the database may not be 100% accurate as insurers are still getting to grips with it, it nevertheless tells a story. 

The insurers have responded by training their surveyors to look for risks specific to MMC, with large buildings assessed on a case by case basis. They examine structures to see if occupiers have knocked holes in the walls to put in flatscreen televisions, additional sockets and loudspeakers, because this could allow fire to spread in and out of cavities. If they are hit by a big claim, they will go back and see if shoddy construction contributed to fire spread and, if it did, seek legal redress. They may decline to insure a building put up by that builder again. The Fire Protection Association, a fire safety and research organisation advising the insurance industry, advises that if fire spread in an incident is shown to be caused by poor workmanship, all other buildings on the same development put up by the same builder should be inspected for fire safety. If anything, the problem could get worse as buildings age and get knocked about by successive owners.

What can be done about this? First, there shouldn’t be a backlash against MMC. Its popularity is down to speed and cost effectiveness. Timber frame has the added bonus of its excellent sustainability credentials. However we need to recognise that MMC is a more highly-tuned beast than masonry construction, which is inherently forgiving of fire (and noise and thermal mass issues), and needs handling with special care.

First up, we should understand where the risks are – for example, how do fires spread inside cavities and what sort of vapour membranes and sheathing boards inside cavities contribute particularly to fire spread? Is wrapping cavity barriers in PVC a good idea, and why do builders install these with gaps between the barrier and the wall or install no barrier at all? Armed with all this knowledge, high-risk materials and construction techniques can be weeded out.

We also need tougher inspection regimes to ensure proven materials and techniques appear on site. ºÃÉ«ÏÈÉúTV control could ask for detailed drawings showing fire stopping measures and ask for photo evidence of installation. It’s required for Passivhaus certification, so why not MMC? It would focus contractors’ minds and demonstrate to insurers that work has been done properly, which would help keep premiums down.

What about existing buildings? This is a much tougher nut to crack because of the difficulty of inspecting cavities for fire integrity. If we can’t prove these buildings are safe, perhaps a database of buildings constructed using MMC is needed so fire brigades know what they are dealing with when they arrive at an incident. Research into the most effective way of fighting cavity fires, such as pumping inert gases into walls, would also help tackle this issue.

History tells us that doing nothing is not an option – as the system building failures of the sixties prove. The day could come when insurers refuse cover on risky buildings, and mortgage providers refuse loans. That is a legacy to be avoided at all costs.