Slopes BUR COAL TAR Slope Felt 0" to 1/2" Per Foot (max.) (0 to 4%) Tarred Organic Felt 0" to 1/4" Per Foot (max.) (0 to 2%) Tar-Glas Felt Premium Tar-Glas Felt 0" to 1/4" Per Foot (max.) (0 to 2%) Tarred Organic Felt with Tar-Glas Ply Koppers does permit slopes up to 1/2" per foot for short-run crickets or saddles for drainage, provided there are provisions for back-nailing and the areas do not encompass more than 15% of the total roof area.  Return to General Requirements and Considerations for the Designer