Why Is Proper Roof Flashing So Important?

Proper valley flashing techniques is one of the most important installation aspects of a new roof. When installed correctly, the roof flashing provides a weather-tight seal against the elements. Poorly constructed/installed valleys may cause roof leaks and are very difficult to repair. Proper valley construction and installation is very important for proper roof drainage.

Where Can A Closed Cut California Valley Be Used?

For the Timberline® Series Shingle installations:

Closed Cut California Valleys are acceptable on slope of 4/12 or greater unless prohibited by local codes.

All other shingles:

  1. GAF does not recommend the use of the California Valleys or any valley that does not follow the guidelines as established by ARMA or the NRCA.

  2. Leaks may occur if California Valleys are installed with the wrong shingles.

How Is A Closed Cut California Valley Constructed?

Valley Valley Valley

  1. Install Weather Watch® or StormGuard® over the entire valley length and then install Roof Deck Protection with a minimum 6” overlap into the valley.

  2.  Install starter shingles and the shingles on the lower slope or lesser height…extend the end shingle of each course at least 12” onto the adjoining roof.

  3. Press shingles into the valley and nail as directed on the bundle with the exception that no nails are within 6” of the valley centerline.

  4. Additional fasteners… place two nails at the end of the shingle that has crossed the valley; one on the nail line, 1” from the edge and one positioned 1” from the edge at the top of the headlap.

  5. Snap a chalk line 2” back from the valley centerline on the adjoining roof.

  6. Install one row of shingles, end-to-end, with the butt edge towards the valley, along the chalk line (see Fig.1).

  7. Fasten the row of shingles in the valley with 4 nails per shingle along the nail line.

  8. To complete the valley, start from the valley and work towards the rake edge. Position each shingle starting a course with the tip of the shingle at the butt edge of the vertically installed shingle. Fasten shingles as usual with the exception of staying 6” away from the valley centerline. Start the first course with a full length shingle; the second course with enough trimmed off of the shingle to maintain a 6” offset from the first course; the third course trimmed to maintain a 5” offset from the second course; the fourth course trimmed to maintain a 6” offset from the third course; and the fifth course should start the pattern over again with a full shingle.

Note: Vertical shingles that have sealant on the top surface in the headlap must be hand sealed along the bottom butt edge in the valley.

Valley Illiustration

Where can I get more information?

GAF Technical Services can assist you… with these and other questions you may have regarding your new roof installation. GAF Technical Services can be contacted at 800-ROOF-411 (800-766-3411). Also, the GAF website is a great resource for just about any question you may have or for additional information you may require. Please visit: www.gaf.com.