Why Does My Roof Leak in the Valley?

What is a roof valley?

A valley is the inside corner where two sloping sections of roof meet. Rain from both slopes drains into it and runs down it to the roof edge.

Any roof with an L-shape, a bump-out or a dormer has them. There are two families, open and closed, usually easy to tell apart from the ground.

A closed valley still has a lining under the shingles. You just can't see it. Every valley type leans on that hidden layer when water gets past the surface.

How much water does a valley handle in a Florida storm?

A lot, and fast. NOAA estimates that about 2 inches of rain in one hour happens on average about once a year in Sarasota and Bradenton, and about 3 inches in an hour about once every 10 years. The valley carries that rain off both slopes that feed it.

Downtown Bradenton is nearly the same (2.00 and 3.00 inches in an hour). In the peak five minutes of a storm Sarasota sees about once every two years, rain falls at a rate of 7.76 inches an hour.

The stream also grows as it runs downhill. GAF builds that into its open valleys: the gap between the shingles starts at 6 inches at the top and widens 1/8 inch per foot toward the eaves to handle the increasing water volume.

How are valley leaks repaired?

By fixing the valley, not the stain: clear it, lift the shingles or tiles along it, replace damaged metal or lining, and lay the covering back to the maker's spec.

Water can enter well uphill of the stain (see how to trace where a roof leak starts). Once the valley is confirmed as the source:

1. Find it and photograph it

   A drone-assisted inspection shows the whole valley from above. The findings go into a written photo report you keep, with a line-by-line estimate.

2. Clear the valley and check the metal

   Debris comes out first, since it may be the whole cause. A clean valley is when holes and corrosion in the metal are easiest to spot.

3. Open it up and replace what failed

   The lining goes in before the shingles, so reaching a torn liner or corroded metal means lifting the shingles or tiles along the valley and replacing what failed.

4. Lay it back by the book

   Nails at least 6 inches from center, the overlapping shingles trimmed 2 inches back, corners clipped, all per that shingle maker's instructions. On tile, the tiles are reset along the new metal.

A single misplaced nail or a clog means a small fix. Metal corroded along its run, or a liner failed in several places, means rebuilding the valley top to bottom, since patching one spot leaves the rest waiting to leak. Either way, a leaking valley is rarely a reason to replace an otherwise sound roof.

Leaks at walls, chimneys and pipe boots are a different repair, covered in why roofs leak at flashing. Valley repairs carry our 1-year workmanship warranty unless the contract says otherwise, and there's no deposit on repairs.