Bituminous-felt built-up roof coverings shall comply with the following requirements-

a) the exposed layer or layers shall comply with the requirements of C.A.S. NO. A30, Bitumen roofing felt surfaced with natural mineral granules of slate or stone rolled into the surface during manufacture in such a manner as to form a closely compacted surface;

b) unexposed layers shall be of mineral-stabilized asphaltic roofing felt or asphalt-saturated felt;

c) such coverings shall be laid on a continuous deck of tounge-and-groove wrought timber boarding or concrete or other approved material, with a minimum fall of 1 in 70 torwards rainwater outlets;

d) when the slope of a roof exceed 1 in 4, the built up roof covering shall be fixed to the deck.