Timber frame inspections: Everything you need for a fire

Health and safety rules for construction sites take full account of the risk posed by stockpiling combustible material. The solution is to either store it in a number of locations or deliver it to the site when it is needed, avoiding the storage problem altogether. So it’s a bit odd that it’s fine to take those materials, join them together into an enormous combustible framework, with plenty of available oxygen, and then hope nobody turns up with the missing third element – ignition.

In Peckham two weeks ago, somebody did. The result was an inferno that set alight two blocks of maisonettes on the other side of the street and caused more than 300 people to flee their homes. About 150 fire fighters were kept busy and the BBC reported a London Fire Brigade spokesperson saying the fire, which melted cars parked in the road, appeared to have “spread very rapidly”. Yes.

I don’t know how much of the 39 flat timber-frame development was erected but I suspect from the extent of the warped scaffold that work was well advanced.

As it happens, the BBC reporters could have cut-and-pasted their copy from articles published in April this year, when a fire caused the evacuation of a residential area in Blackpool. In that incident, 70 fire fighters tackled a blaze that started on a timber-frame flat development. About 150 residents were evacuated to the local sports centre.

At that time, I was carrying out weekly inspections on a four-storey timber-frame development of social housing flats. This was quite a hard job, because it’s difficult to concentrate once you become aware that you’re standing on top of a bonfire.

My town centre regeneration site is pinched between occupied flats, shops and a pub. The timber-framed panels were being pre-insulated in a factory with the usual foam insulation board (a petroleum industry by-product known for its combustibility) to meet Part L standards, and the entire structure was being assembled by on-site carpenters. On this securely hoarded site, the diligent contractors had strategically placed extinguishers, but the risk of somebody wilfully igniting the frame late at night was always present.

Thankfully, that vulnerable stage has now passed, the plasterboarding, external rendering and fire-stopping works are complete and my visits are less troubled, but wouldn’t it make more sense to restrict the size of timber frameworks before this stage?

Of course that might be easier to achieve on a football-pitch-sized site like the one at Peckham, but on a multistorey development, each storey has to be weather-proofed as it’s erected, before the finishings can be applied.

The contractors tell me that timber-frame suppliers required them to apply controlled loading to the frame at each storey, which they expected to settle by only 24mm over the entire height. To achieve this, shrink-wrapped pallets of plasterboard were crane-lifted into strategic locations. This loading strategy was aimed at reducing the settlement after occupation, but I can’t help thinking that the weight of fire-protective plasterboarding would serve a dual-purpose if only it could have been fixed in situ. Alas, plasterboard hates moisture, let alone rain, and even with protected flooring, it is hard to keep it dry. Encasing scaffolds within tarpaulins and fitting them with top hats doesn’t make it easy to lift in framework panels, and my colleague in the fire service tells me they had the devil’s own job trying to hose down a building site fire inside a protected scaffold.

I don’t claim to have a solution to this problem – perhaps the fire brigade will call for temporary site sprinkler systems, perhaps the building inspectors will call for the materials to be treated with fire-retarding chemicals. Whatever happens, timber frame ticks all the sustainability boxes, so we need to find a way of sustaining it long enough to get the building finished.