(1)
Only crawl spaces under 1- storey portions of dwelling units shall be used as warm air plenums.
(2)
Enclosing material in crawl spaces described in Sentence (1), including insulation, shall have a surface flame-spread rating not greater than 150.
(3)
Combustible ground cover used as enclosing material in Sentence (2) shall be covered with noncombustible material. (See Note A-9.18.7.1.(3) and (4))
(4)
Noncombustible material described in Sentence (3) shall
(a)
extend not less than 300 mm beyond the projection of a register opening, and
(b)
have turned-up edges. (See Note A-9.18.7.1.(3) and (4))