Roof Valley Flashing Overlap

With a roll roofing valley keep the nails at least 6 inches from the valley centerline.

Roof valley flashing overlap.

Seal each shingle to the liner and overlapping shingle with a 3 inch wide bead of plastic roofing cement. Flashing against a vertical sidewall shall be by the step flashing method. Valley flashing is metal or sometimes peel and stick material that protects an important area on the roof where two slopes come together to form a valley. Shingles should overlap the valley lining by at least 6 inches.

Slip a piece of sheet metal flashing under the top layer of shingles to protect the bottom layer in the valley while you cut the shingles with a hook blade. An overlap must run downhill the direction of the water flow. Cut bottom of flashing so the entire width of the valley flashing extends approximately 1 2 to 3 4 over the fascia trim board along eaves the following photos illustrate removal and replacement of a closed cut valley with new open metal valley. To splice the pieces add roofing cement to the lower piece and install the upper piece with at least a six inch overlap.

Cut the top layer of shingles along the chalkline. Now nail this first flashing at both its far ends. At the end of the vertical sidewall the step flashing shall be turned out in a manner that directs water away from the wall and onto the roof and or gutter. Laps should comply with the following criteria.

Moving up the valley install any additional roof flashing as required to cover the entire length. Remember to caulk the underside of the flashing with a sealant. Overlap each piece of flashing by at least 6 inches 150 mm. Fold the top of the flashing over the ridge and nail it off every ten inches or so along the outer edge of the flashing now this valley will carry water off the roof and away from the house.

An overlap must run over not under. Step 9 cut corners and apply cement. Install valley battens on both ends of the roof valley then attach first flashing 3 4 inches over the roof flange and another 3 4 inches over the fascia if any is present. The flashing shall be a minimum of 4 inches 102 mm high and 4 inches 102 mm wide.

Step 6 install the flashing. Properly sized and installed valley flashing is key to channeling water safely off the roof. With a metal liner nail 1 2 inch outside the liner. First apply asphalt plastic cement under the overlap area then place and nail down the second piece of flashing.