Many homes use 3-tab shingles as a roof covering. When a roof has two or more planes, each plane meets its neighboring plane at either a hip or valley; hips cover outside corners and valleys cover inside corners. Because a valley collects water from two roof planes, its shingles must shed twice the water that the shingles on the roof plane above the valley must shed. Roofers secure flashing material to the roof's felt paper in the valleys prior to installing 3-tab shingles. Roofers do not nail 3-tab shingles to the center of a valley's flashing.
Things You'll Need
36-inch-wide flashing material
1-inch roofing nails
Unroll a section of 36-inch-wide flashing material over the valley, starting at the bottom of the valley and extending the flashing 12 inches past the top of the valley. Cut the flashing material to size with a utility knife.
Center the flashing material on the valley. Secure the flashing material to the roof's felt paper with 1-inch roofing nails, using a hammer to drive the nails. Place the nails 2 inches from the edge of the flashing material and every 8 inches up both sides.
Extend the 3-tab shingles on one of the roof's planes past the valley at least 12 inches. Secure all of the 3-tab shingles to the roof plane with the 1-inch roofing nails, using the local building codes as a placement guide, except for the shingles covering the flashing material.
Secure the 3-tab shingles covering the flashing material with the 1-inch roofing nails. Keep the nails closest to the center of the valley, at least 6 inches away from the lowest point in the valley.
Extend all of the shingles on the roof's second plane, except for the shingles covering the valley. Secure each shingle to the roof deck with the 1-inch roofing nails, using the local building codes as a nail placement guide.
Lay all of the second roof plane's shingles covering the valley in place. Do not nail the shingles.
Stretch a chalk box's chalk line up the center of the valley. Pull the line tight and snap a line. The line represents the center of the valley and covers the loose shingles' tabs.
Remove the loose shingles from the valley.
Cut each 3-tab shingle to size with the utility knife. Follow the chalk line on the shingle's tabs with the knife. Once the chalk line disappears on the shingle's body, angle the knife toward the top of the shingle's body. Cut all of the shingle's using the same method.
Cover each exposed nail in the valley with roofing cement, using a trowel to apply the roofing cement.
Secure the cut 3-tab shingles to the valley, starting at the bottom of the valley and working toward the top. Drive the 1-inch roofing nails into the part of the cut shingle extending out into the roof's plane, and press the part of the cut shingle in the valley into the roofing cement. Do not drive nails within 6 inches of the center of the valley.