How to Install Roof Valley Flashing

You've come to a valley in your steel roof project and you need to install some valley flashing. When you install valley flashing for a steel roof there are several important steps to follow to avoid premature deterioration of your roof installation. Here's how to install valley flashing so you can enjoy your steel roof for years to come.

Difficulty: Moderately Challenging

Instructions

1. Measure the length of the roof valley and calculate the amount of valley flashing you'll need. Include an extra 4 inches for each overlapping piece that you need to install.

2. Install valley battens on either side of where the valley flashing is installed. Attach the valley to the top flange and extend 3/4 of an inch over the edge of the flange. If the roof has a fascia, extend the valley past it by 3/4 of an inch as well. Scribe the valley to the fascia if needed.

3. Set roof valley flashing in a bead of caulking and use metal roofing nails to attach the flashing to the flange. Overlap each piece the required amount for the slope of roof you are installing. The minimum is 4 inches.

4. Account for the pitch of the roof when laying out the lap on the valley flashing. The lower the pitch the greater the lap needed to protect the roof from ice dams.

5. Spray granules on any cuts made to eliminate premature rusting of the cut material. Caulk in any gaps created by the installation process to avoid water infiltration underneath the installed flashing.

Tips & Warnings

• If your valley will terminate on a lower roof panel, lay that panel first before you install the upper valley flashing.
• Flashing for other types of roofing requires a different technique then the one described here. Check with the manufacturer of the roofing materials to see what type of valley flashing they recommend for their product.