Roofing felt is an asphalt-infused paper that makes up the middle layer of most typical house roofs. It is generally installed on top of plywood or oriented strand board decking and underneath the top layer of shingles. Roofing felt helps waterproof the decking if water becomes dammed up on the roof and runs back under the shingles. It also provides a slight cushion between the shingles and the decking, making your roof more impact-resistant. Do-it-yourselfers can perform the installation.
Strip the shingles from the roof with a pitchfork or flat shovel. Start at the ridge line and work your way down, scraping underneath the shingles and prying up to release the nails. Slide the shingles over the edge of the roof where they can be picked up later.
Remove the old drip edge from the edge of the roof with a pry bar or claw hammer.
Pry up the plastic washer nails that hold the old felt in place, using a pry bar. Any nails that tear through the felt must be pried from the roof or driven in flush to keep from tearing the new felt. Strip off the felt.
Measure the width of the roof face with a tape measure and cut a piece of felt 4 to 6 inches longer than the width of the roof with a utility knife. Nail the first end down 1 to 2 inches from the end of the roof with the hammer and plastic washer nails and roll the felt out parallel to the bottom edge of the roof face, nailing it in place every 10 to 12 inches.
Pull the felt tight as you go to ensure a smooth surface for the shingles to be nailed over. Nail the far edge down firmly and measure and cut the next piece of felt.
Overlap the rows by 4 to 6 inches to provide complete coverage of the decking and nail the second row down with the same technique. Continue adding rows up to a few inches from the peak of the roof.
Roll out and attach felt to the opposite face of the roof, using the same technique until you reach the peak. Cut a piece of felt long enough to cover the peak, using a utility knife, and install the felt folded over the peak and overlapping on top of the top row of felt on each side of the peak.
Trim any excess felt at the ends and along the edge of the roof with a utility knife to make it nice and neat. Install new drip edge along all edges of the roof with a hammer and roofing nails, overlapping the edges of the roofing felt.