How To Install A Metal Roof Valley Flashing

Best practices for sealing the metal roof valley vary based on the slope of the roof.

How to install a metal roof valley flashing. Low slope roofs slope less than 3 12 use tape sealant between the valley trim and the panel. Shingle the other side of the valley the same way. Snap a chalkline 2 to 3 inches past the valley center on the top layer of shingles. Use fasteners to attach the panel to the structure making sure that there is complete compression of the sealant.

Install an underlayment centered in the roof valley. Stop nailing 6 inches from the center. First clean the debris out of the valley including sawdust nails and whatever else is in there. Use 1 inch galvanized roofing nails.

Attach the flashing panel in place at the bottom. With a clean valley you can lay down some peel and stick roofing membrane. Then install a non corrosive metal valley flashing of 24 minimum width lap successive sheets of metal flashing a minimum of 12 inches and seal laps. Apply an approximately 3 inch width of asphalt roofing cement along the sides of flashing and embed shingles in mastic.

Lay one and two tab shingles as you near the valley so full size shingles will run across the valley. Lay the flashing down in the roof valley and start at the lower end of the roof. Install synthetic roofing underlayment or felt paper according to manufacturer specifications and then install the first piece of valley flashing. Fold the top over the roof ridge and cut the bottom along the drip edge metal.

The top joinery of both valleys when they meet on the same plane of roof is shown here.