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Hazard
Fires in thatched roofs

Hazard Knowledge

Thatched roofs are constructed from dry vegetation, usually long straw, combed wheat or water reed. The materials are tightly bundled together and attached using spurges, strips of split timber or reed. To prevent loss of materials this can be covered in a fine mesh. 

Removing long straw thatch is costly and difficult, so a process of spar coating is used. Original layers are left in place and built upon with newer materials. Although wire mesh should be removed during spar coating it may be left in place and all other fixings will remain. This layering process can mean older thatches are over 2m in depth and older thatching material can contain harmful mould spores. Consider the use of RPE to prevent inspiration of mould spores, even when not working in a smoke-filled area.

Thatches built or replaced recently should be built with fire resisting building board (FRBB) to protect roof timbers. This provides a minimum of 30 minutes’ fire protection and should remain in place to prevent firespread to roof timbers. Older thatches may be open boarded, which may allow internal firefighting actions.

Fixings are often combustible, and their Integrity will be affected by fire. Failure of support can lead to large sections of thatch to fall from the roof. The density and depth can mean that thatch weighs more than 34kg per square metre. Personnel should not work beneath burnt or burning sections; consider the use of cordons. 

Wire mesh covering the thatch will conduct electricity and heat. Rusted and torn mesh can cause cuts and infection. 

The ridge of a thatched roof is created using bundled organic material which may burn, and sections of the thatch may collapse as fixings are burnt. This may prohibit the use of roof ladders at thatch fires.