How a Roof Valley Works
Whenever two roof sections angle together, the seam between them forms a low channel called a valley. Water and snowmelt from both adjoining slopes funnel into this single line and flow downward to the eave.
Because it concentrates runoff from a large area, the valley is the busiest drainage path on your roof. Roofers reinforce it in one of two ways:
- Open valley: a visible strip of metal flashing (often aluminum or galvanized steel) runs down the center, giving water a smooth, durable channel.
- Closed valley: shingles are woven or cut across the seam, hiding the channel underneath while an underlayment membrane carries the water.
Why Valleys Matter in the Spokane & Inland Northwest Climate
In our region, the valley is one of the hardest-working and most vulnerable parts of any roof. Several local conditions put it under extra stress:
- Heavy snow load: snow slides and settles into valleys, then melts slowly, keeping the channel wet for long stretches.
- Freeze-thaw cycles: daytime melt refreezes overnight, and ice can lift shingles or back up under flashing.
- Ice dams: valleys are a common starting point for ice dams, which force water sideways and underneath the roofing.
Because of this, a failed or under-built valley is one of the most frequent sources of leaks on Inland Northwest homes.
Common Valley Problems and How They're Prevented
Most valley leaks trace back to a handful of issues that show up after years of snow and ice:
- Worn or corroded metal that no longer sheds water cleanly.
- Debris buildup from pine needles and leaves that traps moisture and dams the channel.
- Missing ice-and-water shield, the self-sealing membrane that should run the full length of every valley.
A proper installation pairs durable metal flashing with a continuous waterproof membrane underneath. When valleys are badly deteriorated, addressing them is often part of a full roof replacement rather than a patch.
Keeping Your Valleys Healthy
You can extend the life of your valleys and catch trouble early with a few simple habits:
- Keep valleys clear of leaves, needles, and branches so water flows freely.
- After heavy snow, watch for ice ridges or icicles forming along the valley line.
- Check ceilings and attic spaces near valleys for water stains after a thaw.
If you notice staining, lifted shingles, or rust in a valley, have it inspected before the next freeze-thaw season. As a GAF Master Elite contractor, DG Contracting offers a free roof inspection and free estimate across Spokane and North Idaho.