Roof Valley Flashing Overlap

A lap is the part of a flashing that covers or overlaps any part of the similarly shaped component and these can be described as an end lap overlap or underlap.

Roof valley flashing overlap.

Shingles should overlap the valley lining by at least 6 inches. Installing drip edge on a humpy old roof dealing with dips and making clean overlaps metal drip edge flashing is installed on the perimeter of a roof to direct water away from the fascia into the gutters and to keep wind blown rain videos roofing wrb flashing drip edge installation on an existing roof. Properly sized and installed valley flashing is key to channeling water safely off the roof. Overlap each piece of flashing by at least 6 inches 150 mm.

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. Step 6 install the flashing. Step 9 cut corners and apply cement. With a metal liner nail 1 2 inch outside the liner.

Cut the top layer of shingles along the chalkline. An overlap must run over not under. With a roll roofing valley keep the nails at least 6 inches from the valley centerline. 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.

Extend entire width of flashing completely to the bottom of the roof valley. The flashing shall be a minimum of 4 inches 102 mm high and 4 inches 102 mm wide. An overlap must run downhill the direction of the water flow. Seal each shingle to the liner and overlapping shingle with a 3 inch wide bead of plastic roofing cement.

Remember to caulk the underside of the flashing with a sealant. To splice the pieces add roofing cement to the lower piece and install the upper piece with at least a six inch overlap. 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. Laps should comply with the following criteria.

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. First apply asphalt plastic cement under the overlap area then place and nail down the second piece of flashing. Moving up the valley install any additional roof flashing as required to cover the entire length. Flashing against a vertical sidewall shall be by the step flashing method.