Note 1. If a cavity closer is also required to function as a cavity
barrier to prevent fire spread, it should provide at least 30
minutes fire resistance, (B. Reg. A.D. B3 Section 6 [Vol. 1] and 9
[Vol. 2]).Note 2. A breather membrane is an alternative to conventional
bituminous felt as an under-tiling layer. It has the benefit of
restricting liquid water penetration whilst allowing water vapour
transfer from within the roof space. This permits air circulation
without perforating the under-tiling layer.Eaves and Ridge---Alternative Treatment