Valley flashing is specialized flashing material, typically metal or a reinforced roofing membrane, installed at a roof valley, the interior angle where two roof planes meet, specifically designed to handle the significant concentrated water flow this location experiences during rainfall.
Because a valley collects water from two entire roof sections, it experiences dramatically more water volume per square foot than a typical flat roof plane, making this flashing’s material quality and installation care particularly consequential.
Two primary installation approaches exist for valleys, open metal valleys that expose the flashing, and closed valleys where shingles are woven or cut to cover the flashing entirely, each with different aesthetic and performance tradeoffs.
What Does Valley Flashing Involve?
- Metal, typically aluminum or galvanized steel, or reinforced membrane material
- Either open or closed installation style
- Adequate width to accommodate expected water volume
- Underlayment reinforcement given the concentrated exposure
Why Is Valley Flashing Important?
Given how much water concentrates and flows through a valley during rain, this flashing represents one of the most critical waterproofing details on the entire roof, and inadequate material, width, or installation quality here disproportionately increases overall leak risk compared to similar deficiencies elsewhere on the roof. This is why valleys are consistently identified as a leading source of roof leaks industry-wide.
Open metal valleys generally shed debris more effectively and can handle higher water volumes than closed valleys, making them a common recommendation in regions with heavy rainfall or significant tree debris, even though closed valleys can offer a more seamless, uniform shingle appearance some homeowners prefer. Discussing these tradeoffs with a roofing contractor helps determine the best fit for a specific home and climate.
Valley Flashing vs. Roof Valley
Roof valley describes the physical intersection where two roof planes meet and slope toward each other. Valley flashing is the specific waterproofing material installed at that location to manage the concentrated water flow the valley’s geometry creates.