Understanding Open Valley Installation
Open valleys are a crucial part of roofing, channeling water off the roof and preventing leaks. Owens Corning provides detailed guidelines for installing open valleys to ensure durability and effectiveness.
Key Steps for Installing Open Valleys
- Self-Adhered Underlayment:
- Material: Use a self-adhered underlayment meeting ASTM D1970.
- Width: Ensure the underlayment is at least 36 inches wide.
- Placement: Center it in the valley and secure with just enough nails to hold it in place. Overlap end laps by 6 inches.
- Metal Flashing:
- Material: Use a minimum 26-gauge metal flashing at least 24 inches wide.
- Placement: Center the flashing in the valley, trimming the lower edge flush with the eave drip edge.
- Overlap: If using multiple pieces, overlap the upper piece over the lower by at least 12 inches, bonding with ASTM D4586 roofing cement.
- Nailing: Space nails 8 to 12 inches apart, 1 inch from the edge. Start on one side and work up, then return to nail the other side, pressing the flashing firmly into the valley.
- Chalk Lines and Bleeder Shingle Installation:
- Chalk Lines: Snap a chalk line 3 inches on either side of the valley, diverging 1/8 inch per foot.
- Bleeder Shingle: Install along the chalk lines with the head lap away from the line, using a standard nailing pattern.
- Full Shingles: Place full shingles with the bottom corner to the edge of the bleeder shingle. Follow the standard nailing pattern, with the nail closest to the valley installed in the nail line of the bleeder below.
- Avoid Roofing Cement:
- Roofing cement is not recommended or required, as incorrect installation can trap water at bleeder end joints.
- If used, apply roofing cement at or above the nail line.
Additional Tips for Installation
- Roof Pitches:
- Certain roof pitches can affect shingle offset when running the book pattern from the bleeder. Ensure shingle offset is no less than 4 inches for correct installation.
Conclusion
Following Owens Corning’s detailed recommendations for installing open valleys ensures proper water drainage and roof durability. Adhering to these guidelines helps prevent leaks and extends the lifespan of your roofing system.
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Disclaimer: This article is intended for informational purposes only. For professional advice, consult experts in the field.
