Why Roof Valleys Leak and How They're Repaired

Why valleys matter

A valley is where two roof slopes meet in an inside corner. Both slopes drain into it, so it carries far more water than the rest of the roof, and it often holds leaves and pine straw. Small mistakes in a valley show up as leaks quickly.

Common causes of valley leaks

• Nails too close to the valley center. Nails placed in the water path open holes right where the most water flows.
• Missing or short underlayment. Valleys should have a self-adhering membrane or valley lining under the shingles. See ice and water shield in NC.
• Poorly cut shingles in closed-cut valleys, with untrimmed upper corners that direct water sideways under the shingles.
• Debris buildup that dams water and pushes it under shingle edges.
• Worn or corroded metal in open metal valleys.
• Valleys that end against a wall without proper flashing.

How valley repairs are done

A lasting repair usually means removing the shingles along the valley, replacing the valley underlayment, and rebuilding the valley — closed-cut, woven or open metal — with nails kept out of the water path. Damaged decking under the valley is replaced first. See open metal vs closed-cut valleys.

Prevention

Keep valleys clear of debris, trim back overhanging branches, and make sure gutters at the bottom of valleys aren't overflowing. Valleys often dump water at one corner of the gutter, which may need a larger downspout or a diverter. See gutter repair.

If you have a stain near an inside corner of the roof, a roof repair inspection will check the valley from end to end.

Frequently Asked Questions