Why Your Windows Leak After Heavy Rain—and What to Do About It

C.E. Larusso
Written by C.E. Larusso
Updated May 19, 2022
beige home with single driveway
Photo: Iriana Shiyan / Adobe Stock

Highlights

  • Confirm that the leak is coming from your window and not the roof, walls, or siding.

  • Damaged or missing flashing or sealant are common causes of window leaks.

  • Make sure your window overhangs and sills are angled to lead water away from your home.

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Your windows connect you to the world outside, but you don’t want to be too connected. Nothing drives this home as much as a big rainstorm. A storm may look beautifully dramatic through your big picture windows from the comfort of a warm, dry living room, but it gets too close for comfort if moisture starts to creep in beneath the panes. 

Windows that leak when it rains can quickly damage your home and lead to urgent electrical hazards and the appearance of mold and rot. You need to nip the problem in the bud as soon as possible. Here are the steps to determine the source of your leak and make the repairs you need before the next big rainfall.

How to Spot a Leaking Window

It may seem obvious: you see dark patches of moisture on the walls or water pooled near the windowsill in the morning after the big storm. You might think the window must be to blame, but it’s not always that simple. In many cases, these may be symptoms of a problem with the wall, siding, gutters, or roof. 

Make sure you know how to distinguish between roof leaks and window leaks and check for signs of the following issues. 

1. Clogged Gutters and Roof Issues

If you see stains along the top of the window frame, check the gutters first: they may be clogged or broken, sending water cascading down the side of your house and damaging the walls and siding. If the gutters look okay, it may be a more complex issue with your roof. Once you rule out the window, you should consult with a roofing contractor to determine the cause of the problem. 

2. Long-Term Leakage 

Beyond the moisture accumulating near your window, look for other telltale signs of long-term leakage. These include rotting wood on the exterior window frame or sill, peeling paint on the walls near the window, and peeling or chipped paint on the interior sill. 

3. Condensation 

Another issue that may appear to be rain leakage is the buildup of condensation on your window panes, created when the heated air in your home comes into contact with cool outdoor air. If you see condensation on the outside of your window panes, it may be a sign of poor insulation or ventilation in your home. Condensation on the inside of the panes indicates that the argon gas that forms an insulating barrier between them is leaking. In this case, contact the manufacturer since your warranty may cover this.  

If you can’t confirm that the window is to blame, call in a local window contractor to take a look before investing too much time or money to remedy what may be the wrong problem.

3 Likely Causes of a Leaking Window

window leak due to rain storm
Photo: William A. Morgan / Adobe Stock

Once you’re certain that the window is the source of your leak, consider three common culprits.

1. Failing Flashing

Flashing is the thin layer of material, sometimes flexible and sometimes rigid, that overlaps the house wrapping on parts of a building susceptible to leaks, such as roofs and windows. Improperly installed, damaged, or even missing flashing neglected during a window replacement is probably the most common cause of window leaks and the first thing to look at. 

Without a reliable and continuous layer of flashing, any moisture that gets behind your siding or works its way into brick will begin to drip into the window opening. If your leak originates from the top of the window, it’s almost certainly due to poor flashing.

Replacing the flashing is a complicated, potentially expensive job for which you need to hire a pro. Speak to a few different window repair companies. The average cost of professional window repair falls between $165 and $550.

2. Poorly Angled Overhangs or Sills

In a well-designed home, it should be difficult for too much moisture to reach your window, even during heavy rainfall. The sloping overhangs you commonly see above windows and door frames are built precisely for this purpose, to direct water away from potential entry points. 

Likewise, it’s why windowsills are angled away from the house. Don’t forget to check the fascia board—the strip of wood behind your gutters—to make sure they’re not angled inward and directing water towards your windows.

3. Damaged or Missing Sealant

Sealant and caulk are other essential tools in the fight against leakage. When a window lets moisture into your home, missing or damaged sealant is often to blame. Inadequate or absent sealant allows the free passage of air between inside and out, undermining energy efficiency and your efforts to regulate the temperature of your home. If you see water coming in from multiple sides of the window, damaged sealant is the most likely cause.

Look for gaps, cracks, or ruptures in the caulk around the frame, between the frame and the glass, and any sealant joints in the stone or brick walls surrounding your window. The good news is that DIY caulking a window is an easy job. Use silicone caulk to reseal areas as necessary.

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