This specification covers the manufacture and requirements of Type II heavy-duty asphalt-impregnated and coated glass-fiber venting base sheet with mineral surfacing on the top side and coarse mineral granules on the bottom side for use as the first ply of a roofing membrane. The mat shall be a thin porous sheet of uniformly distributed glass fibers, with or without the addition of reinforcing strands, or glass yarns, which are bonded with a water-resistant resinous binder, and shall be permitted to contain holes designated for attachment with mopping asphalt. The material shall conform to physical (longitudinal and transverse breaking strength, and diameter and center-to-center spacing of spot-mopping holes, pliability, loss and behavior on heating, ash content, and moisture) and dimensional (mass, width, and area) property requirements. The finished product shall not crack nor be so sticky as to cause tearing or other damage upon being unrolled at given temperatures.

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.