The junction between a compartment wall and the roof of a building should be capable of restricting fire spread between compartments. A compartment wall should be taken up to meet the underside of the roof covering or deck and fire stopped where necessary at the wall/roof junction.

A compartment wall should not be stopped at ceiling level while using a cavity barrier in the roof space to continue the line of compartment to the roof. The construction of the wall, particularly between any ceiling and the roof, should not contain imperfections that would provide a route for fire penetration or premature failure of the fire resistance performance of the wall. The gap between the wall and the underside of the roof should be as small as practicable (generally not greater than 50 mm) and be filled with suitable fire stopping material over the full width of the wall.

Where structural roof members such as beams, purlins and rafters are built into or carried across a masonry or concrete compartment wall, any openings for them should be as small as practicable and any gaps should be effectively fire stopped with non-combustible fire stopping material over the full width of the wall. Where a trussed rafter supporting a roof is carried across a compartment wall it should be designed so that failure due to fire in one compartment will not cause failure of any part of the truss in another compartment. No structural roof member should be carried across a compartment wall which is also a separating wall.

The design and detailing of the junction between a compartment wall and any roof valley, gutter or other roof configuration, should be carefully considered so as to ensure that a means is not provided at the junction for premature fire spread between compartments.

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. To reduce that risk, the junction between a compartment wall and a roof should be constructed in accordance with the following:

(a) a zone of the roof at 1.5 m wide on both sides of the wall should have a covering of class BROOF(t4) (European class) or AA, AB or AC (National class) (see table A5 to Appendix A) on a non-combustible (see table A8 to Appendix A) sub-strate or deck. The compartment wall ,should be carried up to the underside of the roof deck and be fire stopped with resilient non- combustible fire stopping material over the full width of the wall (see Diagram 13(A)).

Note: where the roof deck comprises a double- skin insulated sheet, the insulating material directly above the compartment wall should be of limited combustibility (see A18 and Table A7 of Appendix A) for a width of not less than 300 mm which forms a fire stopping seal to the cavity between the inner and outer skins. In the case of a non-insulated double skin roof deck, similar fire stopping should also be provided.

(b) in buildings not more than 15 m high (see Diagram 37, Appendix C) which are used as dwellings, residential (except institutional), offices, or assembly, timber tiling battens or combustible boarding not exceeding 25 mm in thickness used as a substrate to the roof covering may be carried over the compartment wall, provided that they are fully bedded in mortar or other suitable non-combustible fire stopping material for the full width of the wall, and any cavities within the thickness of the roof, above and below the sarking felt or similar membrane along the line of the wall and at the eaves are adequately fire stopped (see Diagram 13(B)).

(c) As an alternative to (a) or (b) above the compartment wall may be extended above the line of the external roof surface by a height of not less than 375 mm to form a parapet wall (see Diagram 13(C)).

(d) As an alternative to (a), (b) or (c) above for any building type, any other system which has been shown by test to be equally effective in restricting the spread of fire at a compartment wall/roof junction may be used.

3.2.5.11 Junction of compartment wall and roof