Roof felt, or tar paper, as it is commonly called, is a waterproof fiberglass product impregnated with an asphaltic tar compound and is used for temporary roofing or as an underlayment under shingles or other permanent roofing materials. Here is how you install it.
Steps
1 Figure your roof area, and calculate how much felt you will need for the job .
2. Clean the roof decking of any debris, protruding nails, or other objects or materials that will damage the roof felt .
3. Make sure the surface is dry. Never apply roof felt over wet or damp decking, as this condition will cause the decking to warp or buckle, and possibly rot.
4. Replace any damaged or rotten material on the roof decking
5. Begin at the bottom of the decking, on one end, and roll the felt length way, along the lower edge of your roof. For hip type shed roofs, begin at the hip, allowing a foot or so of the felt to hang over the hip
6. Allow the lower edge of the felt to overhand the eave about 1/2 to 3/4 inch so water will drip off without wetting the decking underneath.
7. Tack the end of the felt where you begin rolling it to hold it in place while the rest is unrolled.
8. Pull the felt tight from the opposite end, taking care not to rip it, but making sure it lays flat on the roof surface.
9. Nail the felt with simplex or plastic cap felting nails. These should be spaced at about 12 inch centers along the bottom edge, and 30-36 centers along the top, since subsequent overlaps will be nailed through the top of the last layer applied. Be careful to drive nails flush and not penetrate the felt, or you will have a leak.
10. Cut the felt at the opposite end of your roof, and roll felt back in the opposite direction, allowing about 4 inches of overlap to the first layer. Most roof felt has guide lines stencilled on it to ensure you apply it in straight, parallel lines.
11. Overlap the ridge of your roof about one foot, then apply the material in the same manner on the opposite side.
12. Cover all nail heads with a roofing mastic or tar if this is going to be more than a temporary waterproofing measure.
Tips
Use a heavy duty felt for long term weatherproofing. Felt comes in either 15 pound or 30 pound ratings, and the 30 pound, as the name implies, is twice as strong as the 15 pound.
For a more permanent roof coverage, use roll roofing, which has a mineral aggregate coating to stand up to the elements for a longer period of time.
If the roof felt tears, cut a piece large enough to cover the tear with lots of overlap, slip the top under the next lap above it, and nail into place.
Warnings
Never step on roof felt before it is securely nailed, as it may slide, causing you to fall off the roof.
Use ladders with caution, and have someone available in case of accidents.
