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Hazard

Fires in timber buildings under construction

Hazard Knowledge

Through advances in technology and engineering, timber buildings are becoming more common. Rather than the traditional timber post and beam frame, they now use many different types of construction. The BRE knowledge sheets contain information on this type of construction method.

Timber buildings may include:

  • Structural insulated panels
  • Cross laminated timber
  • Glued laminated timber
  • Laminated veneered lumber
  • Gang nailed timber truss
  • Engineered timber joists

Timber construction is sometimes used when extending buildings that were constructed using more traditional methods. They may be extended at ground level or as an additional structure on the top of an existing building.

New builds could also have lower floors of traditional masonry or steel construction, with upper floors using timber construction methods.

 

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Figure 7: Timber frame extension on a traditionally constructed building - photograph courtesy of the Building Research Establishment

 

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Figure 8: The same building following a fire in the timber frame extension - photograph courtesy of the Building Research Establishment

Timber construction relies on passive and active fire protection, which should be in place in a completed building. However, if the timber construction is incomplete, without elements of fire protection, the timber provides a combustible fuel source. Refer to National Operational Guidance: Fires and firefighting for information on fire loading.

Previous incidents, such as a new development of flats in Colindale, North London in 2006 (image below) prove that the physical principles and phenomena of fire are fairly consistent and not restricted by size.

 

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Figure 9: Timber building under construction at Colindale, London - photograph courtesy of London Fire Brigade

Collapse

The speed of combustion may result in a rapid and sudden collapse, not just from timber burning through, but also at the points where different structures are joined. This can be due to the fixings themselves or because the timber in the area of the fixing has burned away. The heat generated means that other structural members may collapse, along with any scaffolding or temporary supports.

The collapse of a timber building may also impact on scaffolding, other temporary structures, and plant and machinery, such as cranes and lifts.

Access and egress routes

Due to the speed of fire development in timber buildings, access and egress routes may quickly become compromised. This may impact on the evacuation of the building, and on access and egress routes for firefighters or fire and rescue service vehicles.

There may be a temporary external means of escape for a timber building, provided for use until the permanent means of escape is completed, but this may become quickly compromised in a fire.

External firespread

Building regulations provide guidelines for separating distances between existing properties and newly constructed timber buildings. However, the radiated heat or firespread may affect adjacent or adjoining property, vehicles, street furniture and road surfaces. Large volumes of flying embers (firebrands) may travel some distance from the initial incident, resulting in spot fires. For further information refer to the hazard of 'External firespread' in National Operational Guidance: Fires in buildings.