1.1 This specification covers asphalt-impregnated and coated glass-fiber base sheet with fine mineral surfacing on the top side and coarse mineral granules on the bottom side for use as the first ply of a roofing membrane. These base sheets provide for the lateral release of pressure in roofing systems because they are not solidly attached and the coarse granular surface provides an open, porous channel in the horizontal plane beneath the membrane. The base sheets may be with or without perforations or embossings.

1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.