(1)
Except as required in Sentence (2), when underlay is used beneath shingles, it shall be
(a)
asphalt-saturated sheathing paper weighing not less than 0.195 kg/m², or
(b)
No. 15 plain or perforated asphalt-saturated felt. (See Note A-9.26.6.1.(1))
(2)
Underlay used beneath wood shingles shall be breather type.