Junction of compartment walls and roofs

If a fire penetrates a roof near a compartment wall there is a risk that it will spread over the roof to the adjoining compartment. Where a compartment wall meets a roof it should – (a) where the roof covering has a designation of AA, AB or AC (see paragraph 5.21), on a substrate or deck of a material of limited combustibility, for a width of not less than 1.5 m on either side of the junction – be taken up to meet the underside of the roof covering or deck and the junction fire-stopped [see Diagram 4.2(a)]. Where double skinned insulated roof sheeting is used it should incorporate a firebreak formed by a band of material of limited combustibility not less than 300 mm wide centred over the wall. Note – Thermoplastic rooflights which by virtue of paragraph 5.25 are regarded as having an AA (National class) designation or BROOF(t4) (European class) are not suitable for use in the zone described above. However, where the building is of Purpose Group 1, 2(b), 3 or 5 and is not more than 15 m in height a combustible substrate of timber boarding, wood wool slabs or timber tiling battens may be carried over the compartment wall provided it is fully bedded in mortar, or no less suitable material, over the entire width of the wall [see Diagram 4.2(b)]; or (b) be extended up through the roof to a height of not less than 375 mm above the top surface of the roof covering [see Diagram 4.2(c)]. In paragraph (a) where roof support members pass through the wall they should be fire protected for a length of not less than 1.5 m on either side of the wall in order to avoid distortion at the junction.