Home > How To > Roofing > Underlayment for Shallow Roofs Roofing Posted on: September 11, 2015 Field Guide Sample Underlayment for Shallow Roofs On roofs from 2:12 to 4:12, start with a 19-in. starter course, then lap succeeding courses by 19 in. With a standard 36-in. roll of felt, this will provide double coverage. Visit the JLC Field Guide or a complete professional reference guide on Roofing with Asphalt Shingles.