A valley is the channel where two roof slopes meet at an inward angle. Rain and snowmelt from both slopes run into it, so it carries more water than any other part of the roof. A small flaw that would never matter on an open slope can leak badly here.
Two ways valleys are built
In an open valley, a strip of metal runs down the channel and the shingles stop short of the center, leaving the metal exposed. In a closed valley, shingles cover the channel, either woven across it or cut along a line. Each style works when it is built well. Each has its own weak points.
Why valleys fail
- Debris piles up. Leaves, seeds, and twigs collect in the channel and hold water against the shingles. Water that cannot drain can back up under the edges.
- Wear concentrates in the center. Most of the runoff travels down the middle of the valley, so granules wear off faster there.
- Metal rusts or gets punctured. Exposed metal can rust through, and a dropped branch or a careless boot can poke a hole in it.
- Nails in the wrong place. A nail driven too close to the center line gives water a direct path through the roof.
- Poor cutting or lapping. Shingles cut crooked at the edge of an open valley, or lapped the wrong way, let water slip under.
Valley failures are a common form of roof flashing leaks, so an inspection should include all flashing details.
Signs of a valley leak
Inside, the stain usually sits where two roof planes meet above that room. It may show up mostly in heavy rain, when the valley is carrying its full load. Outside, look from the ground for a worn, dark strip down the center, shingle edges that have curled along the channel, or debris sitting in the low spot.
Keeping valleys clear
Trim branches that hang over the roof, since they drop most of the debris. Keep the gutters at the bottom of the valley open, because a clogged gutter can push water back up the channel. Clearing a valley means getting onto the roof, so hire someone to do it rather than climbing up yourself.
What the repair involves
A roofer clears the debris, then checks the metal and the shingles along the channel. A small puncture or a few worn shingles can be repaired. If the metal has rusted through or the shingles along the valley have worn down, the valley is re-lined and the shingles replaced. Dabbing sealant on a worn valley holds for a short time at best. For other wear patterns, see common asphalt shingle roof leaks.
One more point: if the valley is badly worn and the rest of the roof is old too, that wear is worth noting. It can be a sign that the roof as a whole is near the end of its life, and you may want to plan for that rather than keep patching.
Have a valley looked at
Call Roof Leak Repair Carol Stream IL at (630) 866-1445 if a stain lines up with the spot where two slopes meet. Our roof leak repair service covers valley re-lining and shingle replacement.
Carol Stream Leak & Restoration is a free referral service. We connect Carol Stream homeowners with independent local roofing contractors — no fees to you, ever. Call (630) 866-1445 for fast help with a roof leak.