How to Apply Underlayment to a Roof
Installing roofing felt, or "tar paper," is an important step when roofing a building. Here's how to do it.
Before applying roofing, you'll need to cover the sheathing with roofing felt, also often called "tar paper." Most local codes call for using 30-pound felt. Some roofers prefer to attach felt underlayment with 1-inch roofing nails or special nails with plastic washers, but most codes allow staples, which are easier to drive. For the lower portion of the roof—especially the part that overhangs the eaves and is susceptible to ice dams—it is a good idea to apply self-stick waterproof shingle underlayment (WSU), also called ice guard.
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 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.