General Installation Instructions for Atlas Felt Underlayments
Use saturated felt to provide a smooth surface on which to nail shingles and as temporary waterproofing in case of rain. A layer of felt must be applied to a wood deck to provide a vapor retarder between the wood deck and the asphalt fiberglass shingles. Without the felt layer, the wood planking or plywood deck - dried by heated temperatures found in most attics - will draw moisture (including tar and oils from the asphalt) from the shingles. The result will be shingles that are prematurely worn, cracked, brittle, as well as stuck to the wood surface when you attempt to remove them.
Beginning at a bottom corner of the roof, lay felt courses horizontally. Carefully cut off the binding - but don´t cut into the roll - and unravel 2 or 3 feet of the roll. Position the roll of felt so that it can be rolled across the bottom of the roof, even with the eaves. Kneel and hold the roll in both hands. Maneuver the felt into position so that it covers the deck right up to the edge of the rake and eaves but not over the sides of the building.
When you are satisfied that the roll is positioned properly, drive about five nails into the top right-hand corner of the felt. Roll out the felt no more than midway (perhaps 25 feet or so) across the average-size roof. If there is any wind at all, roll out the felt only about 10 feet.
Never walk on felt that has not been nailed down. Pick up the roll with both hands. Pull, straighten, and align the felt along the eaves. Be sure that there are no wrinkles. From behind the roll, reach over and nail down the top of the strip with roofing nails spaced 6 to 8 inches apart. Nail the middle and bottom of the felt similarly.
Roll out the felt toward the other end of the roof. Leave yourself enough room to pull the felt free of wrinkles and set it even with the eaves. Repeat the nailing pattern and remember not to walk on unnailed felt. Unravel a few more feet of felt and cut it with a utility knife. Trim any felt that overlaps the rake. Nail down the last few feet of the first course of felt.
Position the next course of felt so that there is a 2" overlap of the first course of felt. Use the lines printed on the felt as guidelines for lining up the courses. The bottom of the second course of felt should be on top of the first course so that any moisture will flow over the layers of felt.
Roll out a few feet of felt and align the edge of the felt along the rake and the first course. Remember to leave a 2" overlap. Drive about five nails in the top right-hand corner and roll out the felt about halfway (perhaps 25 feet) across the roof. Stand on the first course of felt and work with the second course of felt above you. It is not necessary to completely nail the top edge of the course. A few nails to hold the top in place will be adequate because each top row will become a bottom row once you add another course of felt.
Nail down the bottom and middle of the second course of felt with a pattern of nails every 6 to 8 inches. Remember: never walk on felt that has not been nailed down. Continue laying felt over the remainder of the deck using the same techniques. When you reach the top course, lap about 6 inches of felt over the ridge top. The longer the deck will be exposed to the weather before shingles are applied, the more important it is to lay the felt so that the deck is watertight.
Using a utility knife, slice any wrinkles and nail the felt so that it is smooth. If the deck will be exposed to the weather overnight or longer, apply a very thin coat of asphalt-based roofing cement to waterproof the areas where cuts have been made.
Do not use roofing cement to patch newly installed felt if you will be reshingling the deck the same day. Cement takes several hours to dry and wet cement might ruin your chalk line when you snap lines over the areas. Also freshly laid asphalt-based cement would certainly stick to the line and make it impossible to rewind. If there are cemented areas that must have chalk lines over them, nail a piece of scrap felt over the cemented areas. The deck will be waterproof and the chalk line will remain clean.
When you lay felt in a valley, make certain there are no rips or large wrinkles in the felt. Before you apply the horizontal sections of the felt, install a vertical length of felt down the center of the valley. Several sections of felt can be used, but be certain to overlap the higher sections several inches so that any water will run over the top of the felt.
Very carefully cut off the horizontal sections of the felt at an angle as you reach the center of the valley. If the roof will be exposed overnight or longer, cover nail heads in the valley with a dab of roofing cement.
KEEP ROLLS DRY AND COMPLETELY PROTECTED FROM THE WEATHER. If work is to be done in cold weather, rolls of roofing should be placed in a warm place for 24 hours prior to application.