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A valley is where two roof planes meet and hand all of their water to one channel a few inches wide. It moves faster there, it carries granules with it, and it finds any fastener placed in its path. It is also built three different ways, and which one is on the roof decides what a repair can be before anything else is discussed.
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What this covers
An open valley runs metal down the center with the shingles cut back either side. A closed-cut valley runs one plane across and cuts the other back over it. A woven valley interlaces the courses from both planes. They are repaired differently and they fail differently, so identifying the construction comes before a scope is written.
Two planes of collected water pass through a channel a few inches wide, at speed. That is why granule loss shows in a valley before it shows in the field, and why a detail that would be harmless in the middle of a slope is a leak in the valley line.
Nails set inside the valley are one of the more common defects found up there — each one a hole in the fastest-moving water on the roof, sealed with whatever was to hand. They are found by looking rather than by testing, and they change the repair from a patch to a section.
What to know
In a closed-cut or woven valley the courses are interlocked with the planes either side, so lifting a failed section means unsealing shingles up-slope on both roofs. The honest repair is usually a length of valley taken from ridge to eave rather than a square cut around a stain, and an estimate that promises the second is describing something that will be the first.
Current practice puts a self-adhered membrane under a valley precisely because that is where water backs up and where fasteners land. On an older roof it may never have been there, or it may have been skipped. A repair is the moment when that gets established, and it belongs in the record either way.
The classic valley backup in colder markets is ice. Here it is leaves. A valley that dies into a gutter under a tree line packs solid every autumn, water backs up under the cut edge, and the failure gets reported the following spring as a roof leak. The repair and the maintenance interval are two separate outputs of the same visit.
Choose a starting point
A short, non-diagnostic guide for working out what kind of assessment conversation to prepare for.
Decision support
Four situations, and the sensible next move for each. It does not diagnose a roof, decide insurance coverage, or stand in for somebody looking at the property.
Questions
Rarely. The valley is built out of the courses either side of it, so reaching the failed part means releasing them. A contractor promising an isolated patch in a closed-cut valley is describing something that is not how the assembly goes together.
Both work when they are built correctly. Open valleys are easier to inspect and easier to repair, and metal is visible from the ground. Closed-cut valleys are usually chosen for appearance. The difference that matters to an owner is repairability, which is worth knowing at replacement rather than at the first leak.
On a new roof, some loose granule wash is expected and settles down. Continuing accumulation, particularly with visible mat showing on the slopes above, is wear rather than shedding. Photograph it, date it, and compare in a year — that comparison is worth more than any single opinion about it.
Two things that get confused with each other. The roofing answer is whether the valley, its underlayment and its cut edge are sound where water backs up behind the debris. The maintenance answer is the interval at which that outlet is cleared, and possibly an additional outlet beneath the valley, because a valley hands two planes of water to one point. Doing the first without the second means repairing the same detail again.
Assessment request
Short, routing-only questions. Nothing here asks you to diagnose the roof yourself.