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.