In-place Weights per 100 sq. ft. In order that the "Felt Shall Not Touch Felt" standard is met, experience shows that an average in-place continuous firmly bonded interply film of coal tar pitch of not less than 20 pounds per square (9.1 kg/9.3m2) is adequate for membrane construction. This weight should only be used as a guide. More importantly, attention should be given to proper kettle and point of application temperatures for sound built-up roof constructions. For coal tar, experience shows that an average in-place top pour of coal tar pitch of not less than 70 pounds per square (31.8 kg/9.3m2) is adequate.  Return to Application Considerations and Specifications