(1) Where a crawl space is unheated, a ground cover shall be provided consisting of not less than,
(a) 50 mm of asphalt paving material,
(b) 100 mm of 15 MPa Portland cement concrete,
(c) Type S roll roofing, or
(d) 0.10 mm polyethylene.
(2) Joints in sheet-type ground cover required in Sentence (1) shall be lapped not less than 100 mm and weighted down.