Why Does My Roof Leak Only When It Is Windy?

Why does a roof leak only when it is windy?

Wind pushes rain sideways and uphill. Rain that would run off a roof in calm weather gets driven into gaps that normally stay dry.

A roof sheds water the way a coat does: rain lands high and runs down over the layers. Every joint is built so the upper piece covers the lower one. That works when rain falls straight down. When wind pushes the rain, water moves sideways, and it can go up and under those layers instead of down over them.

The Florida Division of Emergency Management explains it with numbers. It says rain is driven against a house with great penetrating force above 60 mph, and that water can be pushed about 3 1/2 inches up through a crack at 100 mph, about 6 inches at 130 mph and about 8 inches at 150 mph. Those are hurricane speeds. The same thing happens at lower speeds, just over a shorter distance. A gap that is fine in a calm rain can leak in a gusty one.

It also says attic and indoor air pressure is usually a little lower than outside during a storm, which pulls water in through cracks. So wind both pushes and pulls.

Who it affects: any Florida roof, especially one with many vents, pipes and joints for water to find. When it happens: Gulf Coast thunderstorms with strong gusts, tropical storms, hurricanes, and the windy days after winter cold fronts.

How do you figure out where a wind-driven leak is coming from?

Write down the wind direction, the time and where the water shows. That pattern tells a roofer where to look.

You cannot test for wind-driven rain on a calm day, so the notes you take during the storm are the best evidence. Stay safe: do not climb on the roof, and do not go in the attic during lightning or if wiring is wet.

1. Note the wind direction

   Write down which way the wind was blowing. If the leak only happens with wind from the south, look at the south side of the roof and the south-facing walls.

2. Note where the water showed up

   Which room, which wall, which part of the ceiling. Take photos with the date. Put a bucket and towels down. For tips, see how to slow a leak until help comes.

3. Check the attic after the storm

   When it is safe, look under the roof deck, near vents, the ridge and the low edges. Step only on the joists. Follow our guide to checking your attic for a roof leak.

4. Look from the ground

   With binoculars, look for lifted shingles, slipped tiles, loose ridge caps, hanging soffit pieces and vents that look crooked.

5. Have the roof inspected on a dry day

   A roofer can look at the vents, ridge, flashing and soffits, test in stages and find a spot that only opens in a gust. A tile roof often needs a drone look first.

What should you do after a storm leak?

Dry it, photograph it, and get the roof looked at on the next dry day.

Wind-driven leaks are easy to dismiss because they stop when the weather does. But the water that got in does not leave. It can soak insulation and wood, and the EPA says damp materials should be dried within 24 to 48 hours to prevent mold growth. Our page on hidden storm damage lists what to look for after a storm.

Coastline Roofing repairs roofs after storms, including temporary repairs and tarps when a roof cannot wait. We inspect the roof and send a written photo report showing where water got in. See our roof repair and emergency tarping pages.