Coated felt roofing, commonly referred to as underlayment or tarpaper, is asphalt-impregnated paper that provides a second layer of protection under the main roofing. There are a number of different types and weights of felt roofing, and the shingle manufacturer usually provides instructions as to which type is needed.
Apply the first row of roofing felt by starting at the bottom of the roof area, aligning it on one bottom corner and applying five or six staples. This will hold the felt roofing in place but still allow you to straighten it as needed.
Roll the roofing felt to the other side of the roof along the front edge. Pull the felt out smooth and cut it so that it is even with a rake edge. The sidelap should be about 12 inches. Tack the edge down with plenty of staples.
Glue down the headlap area of the first row near the gutters with roofing adhesive in order to protect against water backing up from the gutters. Then, move along the first row and tack staples evenly to affix the coated felt roofing to the deck.
Apply the next layer the same way by overlapping between two and six inches at the headlap and about 12 inches on the sidelap. Continue up the roofing until you reach the ridge.
Apply the paper across the top of the roof's ridge and staple it on the other side. If necessary, cut the felt roofing for a ridge vent at the spot of the opening.
Apply the felt roofing at valleys and hips by laying the felt across the area to the other side, carrying over at least 18 inches. If a vertical wall meets the roofing area, continue laying the roofing felt up the wall area for roughly five inches. Continue to tack the roofing felt in place with staples.
Ensure the roofing felt, once applied, is evenly tacked in place and there are no large bubbles before moving forward with applying your shingles.
The minimum overlap on the top edge, known as a headlap, of the coated felt roofing is two inches. However, while a six-inch headlap will cost you more in terms of material, it will protect your home much better.
Do not lay roofing felt on a wet plywood deck because the moisture will turn into steam that could potentially blow a hole through the underlayment and eventually distort and bubble shingles.