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Richard Nelson By Richard Nelson • October 25, 2017

A Valley on My Roof? - Roofing Language Explained: Valleys

Shingle roof with woven valley
Valley without metal flashing.


Valleys and Flashing explained in simple terms.

It may sound odd to learn that you have a valley on your roof. The place where two roof surfaces intersect is called a valley. This is one of the most common areas for a roof to leak. Non-permeable materials such as metal sheets or roof rolls are placed over these joins to seal out moisture. 

Weathered shingles and valley with flashing
Asphalt shingles and metal flashing on a damaged Canadian roof. 


Definition of a Roof Valley

The greatest portion of a roof is a flat expanse that is covered with a non-permeable material, such as asphalt shingles, metal tiles or slate tiles, to protect the roof structure and the interior of the building. When two roof surfaces meet, a valley is created. The valley creates a channel that allows moisture to run off the roof.

Importance of Flashing in Valleys

Valley with metal flashing to protect from rain damage
Water flows onto and down the metal flashing in the valley.

If your roofer says to put flashing in the valleys, the contractor is concerned that moisture may penetrate between joins. Flashing is placed in a valley to create an impermeable seal. Valleys often deteriorate more quickly than other portions of a roof, particularly if leaves and debris build up in the channel. If valleys become clogged, water will not run off. As debris accumulates, the flashing weakens and corrodes.

If your roof leaks, a roofing expert can inspect the roof surface and valleys to find the source. Roofr works with vetted roofing contractors who are licensed to work in your area. Each independent contractor provides a guarantee for labor and a warranty for materials. Roofr makes sure you're satisfied with the quality of work. Our goal is to hear you say, "My roofer did an excellent job. My roof looks great, the valleys are well-sealed and there are no problems."

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