What Is Dead Valley?
Dead valleys occur where roof geometry traps water: a dormer or addition tucked behind a chimney, two slopes converging against a wall, or a porch roof meeting the main house at a shallow inside corner. Water arriving there has no slope to carry it out, so it slows, pools, and collects debris — and every shedding-based material (shingles, tile, lap metal) depends on moving water and fails when it stands. Dead valleys are almost always born in design or created by additions, and they announce themselves as the one spot that leaks repeatedly no matter how often it is re-shingled or caulked. The competent treatment changes the rules in that area: strip it, install a fully adhered or welded membrane (ice-and-water shield at minimum, TPO or modified bitumen for larger pockets) carried well up the adjoining walls and under the surrounding shingles, and keep it cleared of leaves. Homeowners can spot candidates as roof pockets where debris accumulates, and should treat any repeat leak near one as geometry, not material.
Important Distinction
Note: A dead valley is not a normal valley: a valley is a channel that drains, a dead valley is a pocket that cannot. Shingling a dead valley is a common original-construction error — the fix is a welded or self-adhered membrane in that area, not better shingles.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Dead Valley Relates to Other Topics
A dead valley is where two slopes drain into a spot with no exit path; leaves and granules settle there, the debris dams the water, and a shingle roof ends up holding a pond it was never designed to hold.
The right fix for a dead valley is usually flat-roof membrane in that one spot, even on a shingle roof - shingles shed moving water and cannot seal standing water, so the material has to change where the drainage does.
Related To Dead Valley
A true valley drains: two planes meet and the water accelerates out. A dead valley is the same meeting with no exit. The first is a normal detail handled with membrane and metal; the second is a design flaw that needs its own engineered fix.
Questions about Dead Valley?
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