Older homes have a charm all their own. There’s just something about the look and feel of a place that’s stood the test of time. But any structure built decades ago will eventually start to show its age.

Especially when it rains.

Leaky window frames aren’t uncommon in older homes. But common or not, it’s a problem that needs to be addressed. Water is incredibly corrosive to a home. Even small leaks can lead to structural damage, mold development, or both.

Drywall water damage can be an intrusive and expensive repair, as can mold remediation. And mold doesn’t need anything more than moisture and organic material to grow.

A leaky window makes it oh-so-easy for mold to grow inside walls—completely out of sight—for some time before it becomes noticeable.

In this article, we’ll explore why you’re likely experiencing a leaky window. We’ll walk you through the process of determining the source of the leak. And we’ll even provide guidance on whether it’s best to repair or replace a leaky window.

Let’s get to it.

Why Is Water Leaking Through the Frame?

Although more common in older homes, newer homes can have issues with leaky windows, too. Even the very best building materials don’t last forever. Almost all windows will start to leak eventually.

There are several reasons a window might spring a leak.

Older Homes

Buildings settle over time. Years of fluctuating temperatures and weather conditions cause wood to shrink and expand. This is all very normal.

However, sometimes this shifting causes a window to misalign with its frame, creating gaps.

Improper Installation

Window flashing has to be installed correctly. If it’s not installed right, it can lead to a leak. Additionally, housewrap or building paper are not adequate substitutes for specially designed waterproof flashing.

If either of these were used, you may have an ineffective barrier.

Compromised Sealant

Broken caulking at the window seams, cracked glazing putty between panes, and an inadequate paint seal along the edges of the glass can all lead to water infiltration.

Some of this is to be expected over time.

Identifying the Source of the Leak

Once you’ve spotted a leak, you need to know what’s causing it. After all, new caulk won’t stop the leak if the issue is caused by a misaligned frame.

Before you can fix the problem, you need to fully understand it.

Roof and Wall Leaks

Window leaks can result from a structural issue somewhere else in the home. You’ll want to check the roof, upper floors and siding.

If you notice water stains on the wall above the window or along the top or bottom of the frame, this usually means there’s a leak inside the walls. From the point of entry, water will run downward, enter the frame, and collect along the flat surfaces of the top and bottom.

The source of a leak like this can be difficult to identify. If you can’t determine where the water is getting in, contact a window professional to help diagnose the issue.

Broken Sealant

Windows leaking at the bottom corner of the frame or where the glass meets the sill typically indicates cracked caulking or glazing. Caught early, this issue can usually be repaired by stripping the old sealant and replacing it.

Unless you’re comfortable around a caulking gun, fixing old caulk or glaze should be left to the professionals. At best, mistakes will look messy. And at worst, your hard work won’t stop the leak.

Window Repair vs. Replacement

Sealant can be fixed without replacing the window. But if the problem is more complicated, the new sealant may not be all that’s needed. This is often the case for wooden windows, which are common in older construction.

Check for Damp or Soft Wood

Start by probing the frame with a screwdriver. Then open the window to check the inside of the frame and sash. If the wood gives under light pressure, it has started to decay and needs to be replaced.

Check for Puckering Drywall or Peeling Paint

If the leak has affected the structure around the window, the best way forward is to call a reputable window replacement company. A window professional will perform a full evaluation to determine whether replacement is in order.

They will also help identify the source of the leak. Although the water may be coming from your window, it could be the result of a larger structural issue as discussed above.

Work With the Right Specialist

Window installers don’t always specialize in the work required to locate and mend a hidden leak elsewhere in the home. You may also need to contact a plumber or waterproofing professional.

Keep in mind that replacing the window without fixing the leak will only lead to similar problems down the line.