When a roof valley needs to be shingled, there are steps to take in order to make it waterproof. When it rains or snows, there is going to be more water in the valleys of the roof than in the other sections. This is because it gives a natural flow to the water as it runs off. Paying special attention to this will ensure that you will not have any problems with your roof after completing it. As a do-it-yourself project, it is not difficult to do, but you must follow certain procedures.
Step 1 - Snap Chalk Line
Before you begin laying down the shingles it must be protected with a metal flashing. This flashing must be about 18 inches wide for adequate coverage on both sides. Snap a chalk line down the length of the edges of the valley nine inches from the center.
Step 2 - Install Metal Flashing
The flashing should be thin aluminum that is easy to bend and work with. Lay the flashing on the valley and carefully use a rubber roller to create the crease for the valley angle. Line up the edges of the metal flashing with the chalk lines and secure with roofing nails. Cut off the excess material with tin snips. Use a six- inch scraper and spread roofing tar along the edges of the flashing for a waterproof seal.
Step 3 - Apply Mineral Roofing Felt
Snap another chalk line that is 18 inches from the center of the valley. Roll out the roofing material and cut it to fit in the lines of the opening. Roll it down the valley and secure with roofing nails. The material should be at the top edge of the valley and the bottom edge. Cut with tin ships or utility knife.
Step 4 - Determine Shingle Lines
Lay a shingle on the valley without nailing it in. Line it up so 1/3 of the shingle is on either side of the valley. Mark each outside edge of the shingle with a marker. Snap a chalk line along these lines as a reference point. Measure out three inches from the valley edge and snap another chalk line on each side. There should be no nails past this three-inch mark.
Step 5 - Install First Valley Roof Shingle
Starting at the bottom edge of the valley, begin laying down the shingles. Cut the tabs off of one shingle and lay it on the bottom edge with a 1/4 inch overhang. Press the shingle into the valley and make sure that it is flat against the surface of the roof. Place a roofing nail in each corner and one in the center on its appropriate side.
Step 6 - Shingle Valley
From this starter shingle, continue moving up the valley roof. The next shingle should be directly atop the first one. Each successive shingle should be then placed with a six-inch overlap, or until the adhesive strip contacts the bottom of the shingle tabs. Continue until you reach the top edge of the valley roof.