A roof that leaks only in heavy rain usually has a small opening that light rain never reaches. In a downpour, water runs deeper and faster, backs up behind chimneys and walls, and wind pushes it sideways under shingle edges and flashing. The usual culprits are wall or chimney flashing, clogged valleys, cracked pipe boots and roofs that are too flat for shingles.
Why heavy rain finds gaps light rain misses
In a light rain, water runs down the roof in a thin film and drains before it builds up. In a hard storm, the roof carries far more water at once. It piles up against anything in its path, like a chimney, a skylight or the wall above a porch roof. It fills valleys and gutters. And wind drives it uphill and sideways, into seams that normally stay dry. Pine Bluff gets more than 5 inches of rain a month from March through May, often in short, heavy bursts, so these leaks show up most in spring.
The most common causes
- Step and counter flashing where the roof meets a wall or chimney
- Valleys packed with pine needles that back water up under the shingles
- Pipe boots with a small split on the uphill side
- Porch and addition roofs too flat for shingles
- Gutters that overflow and push water under the roof edge
- Wind-lifted shingles that lost their seal
Clues that point to the source
- Only with wind from one direction: flashing or siding on that side of the house.
- Near a chimney or fireplace: chimney flashing. See chimney leak repair.
- Under an inside corner of the roof: a valley. See roof valley leak repair.
- Near an outside wall: the roof edge, drip edge or an overflowing gutter.
- Under a porch or addition: a low slope or a bad tie-in to the house.
How to find it
Check the attic during or right after a heavy rain with a flashlight and look for fresh drips or wet wood. Mark the spot. If the rain has stopped, a hose test on one section of roof at a time, with someone watching inside, recreates the storm and pinpoints the gap. See how to find a roof leak from the attic.
Is it dangerous to wait?
Every heavy rain soaks the same spot a little more. Over months that means rotted decking, wet insulation and a stained or sagging ceiling. The repair itself is usually small, often flashing or a boot, so fixing it early keeps it cheap.
Why does my roof leak in heavy rain but not in snow?
Snow melts slowly and runs off gently, so it rarely reaches the same gaps that wind-driven rain does. A leak only in snow points to something else, like ice damming at the eaves. In Pine Bluff, rain is the far more common cause.
Can gutters cause a heavy-rain leak?
Yes. When gutters fill with pine needles and leaves, water in a downpour spills back over the edge and under the first row of shingles. On roofs without drip edge, that water soaks the fascia and the edge of the decking and can show up as a stain along an outside wall. Cleaning gutters before spring storm season in Pine Bluff prevents a lot of these leaks. See gutter leak repair.
Can a roof leak only in heavy rain be flashing?
Yes. Flashing is the most common cause, because water builds up against walls and chimneys only in heavy rain.
Will sealant fix a heavy-rain leak?
Sealant rarely lasts. The lasting fix is correct flashing, a cleared and rebuilt valley or a new boot, depending on the cause.
Why does my roof leak only when it storms with wind?
Wind drives rain sideways and up under shingle edges and flashing that normally stay dry.
How do roofers find a leak that only happens in heavy rain?
With an attic check during rain, or a hose test that recreates the storm one section at a time.