Roof valleys are the lowest spots on certain roof designs. For this reason, they can be more prone to leaks compared to the higher flat planes of the roof.

Pooling Water

Roof valleys can be prone to pooling water. Sometimes the problem is with the design of the roof itself. If the pitch of the valley is insufficient for good water flow, stagnant water may collect. Too many sloped planes leading into a single valley can also cause pooling, as can a valley that doesn't have a sufficient opening at the bottom for drainage of the collected water. Outside issues, such as fallen leaves or debris on the roof, can also block valley drainage and cause pooling.

Over time, that pooled water will seep beneath the shingles surrounding the valley and cause a leak in the home. Fixing the drainage issues is the first order of business. Your roofer may need to clear off debris or add diverters on the upward slopes to divert runoff water to other locations. Once this is done, any damage that has developed, such as water-logged shingles, must be repaired.

Damaged Flashing

Valleys have flashing in order to help protect against leaks since the roof valley is exposed to more moisture compared to other parts of the roof. Sometimes a metal flashing strip is installed, which is similar to what is used around chimneys. In other instances, a vinyl flashing trough may be installed. On some roofs, no true flashing is used, and instead, a series of specially made overlapping shingles covers the valley instead.

Regardless of the flashing type, damage and degradation to it can lead to a leak along the roof valley. Metal flashing, for example, can be warped or torn up by high winds. Vinyl troughs can crack, and shingle covers are prone to the same damage as any asphalt shingle. Repairing or replacing the damaged flashing will solve the leak.

Ice Dams

Some leaks are only a concern in winter. Ice dams form when melted ice and snow can't flow off the roof properly, so it backwashes back up the roof and under the shingles. Clogged gutters are a common cause of this backwash, as is debris caught at the end of a roof valley. Sometimes the debris is nothing more than a clump of unmelted ice or the top of forming icicles.

Cleaning the gutters and making sure there is no debris in the valleys cuts down on ice dam formation. If ice clumps often form at the outlet of a valley, your roofer may recommend installing heat cables in the location to minimize the issue.

Contact a roofing company if you are having issues with leaks along the low valleys on your roof.