Roll roofing can easily become damaged in harsh weather or when debris on the roof encourages premature degradation of the material. If there are only a few damaged areas that you see on the roll roofing, it may be worthwhile to replace a few problem areas rather than replacing the entire roof. Keep in mind, however, that patching these areas is only a temporary fix; start saving for a new roof to apply when the patches fail.
Step 1: Use a metal straight edge and sharpie to mark the perimeter of the damaged roll roofing. To save time, try to extend the perimeter so it forms a rectangle over the damaged area.
Step 2: Cut away the old roll roofing using a utility blade and straight edge. Cut through one layer at a time of the roll roofing until you reach a the layer of roll roofing that appears to be sound.
Step 3: Cut one patch from a piece of extra roll roofing for each layer of roll roofing that you had to remove. Use the removed pieces pieces of roll roofing to act as a template so that you can achieve an exact fit when cutting your patches.
Step 3: Clean away any old adhesive on the surface. Apply a layer of roofing cement to the surface of the exposed roll roofing, then press the patch into place. Be sure to remove any air bubbles within the adhesive.
Step 4: Continue adding patches with roofing cement until the patched area is level with the roll roofing surrounding it.
Step 5: Nail around the perimeter of the patch with short roofing nails, making sure to place a nail in each corner.
Step 6: Cut another patch out of roll roofing extends beyond the existing patches by 3 inches. Apply roofing cement to the back of that patch and press it into place.
Step 7: Place a generous bead of roofing cement around the outside perimeter of the patch. Use a putty knife to feather the roofing cement so it covers and seals the perimeter of the patch.