Underlayment, flashings, and shingles all work together and must be installed in the correct order. If you lay the felt perfectly straight, you can use its lines (instead of horizontal chalklines) to align the shingles. Do not use felt as a temporary protection against rain: If it gets wet it will wrinkle, making it harder to shingle. If you need to temporarily protect a roof, cover it with plastic sheeting or a tarp. When working with a helper, expect to spend several hours to install the drip edge, WSU, and roofing felt on a medium-sized roof. Prep for the project by sweeping the sheathing clean of all debris and making sure there are no nails or splinters poking up. Editor’s tip: Where you meet a hip, apply felt up to the hip and cut the pieces so they fit snugly. Then apply a vertical course of felt along the hip that overlaps on each side. Editor’s tip: When the weather promises to stay dry, many roofers prefer to install underlayment as they go. Apply one or two courses of WSU or felt, install the shingles, then apply more felt when you come within 6 inches of the top edge.
