Don’t be alarmist over timber frame

In 1982, a World in Action television exposé killed the UK timber-frame housing market overnight and it has taken more than 20 years for the industry to recover.

In that programme, poor workmanship was illustrated taking place on UK house building sites. What it failed to show the viewer was the same faults and worse on so-called traditionally built housing sites - which at that time represented 80 per cent of the market.

We all know that wood is combustible. What few people in housing realise is that: a) when we talk about ‘timber frame’ as opposed to ‘traditional construction’ the only difference is that the load-bearing inner leaf of the external wall is timber frame instead of concrete block; and b) timber burns at a very predictable 1/64 of an inch per minute or an inch per hour (25mm per hour).

What this means is that the vast majority of internal partitions, intermediate floors, top floor ceilings, roof frames and stairs in UK dwellings are made from wood and where the wood is used for a structural member its size (cross-sectional area) is designed to provide sufficient ‘meat’ to last at least 30 minutes in a fire.

Where those timbers are between dwellings, they must last at least one hour. This fire resistance is achieved in part by covering the timber with fire-resistant lining boards, for example, plasterboard.

It is fair to say that the cavities on the outside of the frame have to be properly fire proofed with cavity barriers to prevent fire transferring from dwelling to dwelling via window frames and the conventional cavity between the timber frame and the traditional brick-work cladding.

It is worth noting that those same cavity barriers are just as important in traditional construction. Cavity barriers are there to overcome the inherent weakness (from the point of view of fire penetration and transfer) of window and door frames.

Richard Baines, director, Sustainable Development