Installing Pre-shingle Flashings

If you will install an open metal valley, the valley flashing must be installed after the underlayment and before the shingles; follow the instructions here. If you will be installing a woven or closed-cut valley, there is no need for valley flashing. However, a strip of WSU is highly recommended.

Roofers sometimes make their own valley flashings out of sheet metal, but you are better off buying ready-made valley flashing. The type with a center spine (or ridge) works best because it channels water more efficiently and permits expansion and contraction of the metal. Valley flashing with nailing clips prevents puncturing of the flashing, but you can also nail the flashing directly if you do so carefully.

The drip edge along the rake is also installed at this time. In most cases, you will use the same type of drip edge as you used for the eave.

Checklist

Time
1 to 2 hours to cut and install flashings for a valley and rake ends

Tools
Tin snips, tape measure, hammer, chalkline

Skills
Measuring and cutting metal, driving nails

Prep
Apply the underlayment, preferably with a strip of WSU along the valley.

Materials
Valley flashing, roofing nails