Reduction of the number of pitched roof cavity barriers, social housing, Enfield.

My client was adding lightweight steel-framed pitched roofs above existing flat roofs in blocks of 3-4 storey residential flat/maisonettes as part of an upgrade.  The client considered that it did not need to provide cavity barriers at every party wall location, and had appealed to the local building control authority. ADB Volume 2 recommends that the separating elements of adjoining flats possess a one hour fire resistance according to BS 476, and with most timber-joisted roof construction this would mean that a one hour fire resisting vertical barrier (cavity barrier) would need to be erected above each party wall. With a strong background in assessing the fire resistance of elements of construction from previous work at the governments’ Fire Research Station (see My Publications on this website) I assessed that there would be (with slight modification) at least one hour fire resistance in the existing roof construction for fire attack upwards from the flat of fire origin and then downwards on the other side of the party wall. I made a thorough inspection of the building and prepared a carefully argued report covering life safety, property protection and fire-fighting that was accepted by the Appeals Panel of the LDSA. I was then able to agree with the client that, for this particular project with its robust construction, cavity barriers were only needed at nominally 20m centres. This resulted in cost savings of more than £50,000.

Client: Langley Waterproofing Systems Ltd.