Vermiculite concrete lends itself to providing both drainage slope and high insulating values to various types of precast concrete units such as core type structural slabs, channel slabs, and prestressed single and double tees. Vermiculite cast-in-place concrete provides smooth surface for applying the built up roofing membrane. Should additional venting be required the use of roof vents similar to McKinley Roof Vents should be installed -- one vent for each thousand square