Window Leaks When It Rains: Finding the Source

A window that leaks in the rain is letting water past one of five places: the seal between the glass and the sash, the joints of the frame, the drainage at the bottom of the frame (the sill track and its weep holes), the sill itself, or the flashing that ties the window into the wall. The first three are often things a homeowner can check and sometimes fix. A leak at the flashing, or water showing up in the wall beside or below the window, usually points to how the window was installed.

Not all water is a leak. ProVia's care guide says several window styles let water into the sill area by design, capture it and drain it to the outside, and that water in the sill does not indicate a problem unless it overflows onto the interior sill or wall ³. The question is where the water ends up, and the steps below trace it.

Step 1: Note where and when the water appears

Where the water shows up says a lot about where it came in:

• On the glass or the inside of the sash, near the edge of the pane: look at the glazing seal.
• Pooled in the bottom track, spilling over the inside edge: look at the drainage first.
• At a corner of the frame: look at the frame joints.
• Below the window, on the wall, or as a stain on the ceiling under it: water is likely getting behind the window, which points to the flashing or the wall around it.

Also note the weather. A leak only in wind-driven rain from one direction is different from one in any rain. And rule out condensation: water that forms on the inside of cold glass in winter comes from indoor humidity, not rain. Window condensation covers that.

Step 2: Check the weep holes and sill track

Weep holes are small openings that let water drain out of the frame, usually flat holes or slots at the outside bottom of the frame ¹. The Department of Energy's Building America Solution Center says that when they are clogged or caulked, trapped water can build up in the frame and eventually damage the framing, sheathing and insulation ¹.

Its test is simple: mist the outside glass, or pour water into the inside track, and watch whether water comes out of the weep holes ¹. If it does not, the guide suggests removing any caulk over the holes, loosening debris with a flathead screwdriver or crochet hook without pushing it deeper, clearing the channel with a pipe cleaner or small brush, and testing again ¹. ProVia's care guide likewise says to keep the sill track and weep holes clear of dirt and debris so water can flow to the outside ³.

The most common self-inflicted cause is caulk. The DOE guide warns that weep holes can be caulked over by accident ¹, and Andersen's installation article says sealant should not go on the bottom flange of a window if water is to drain out of that area ⁴. Caulk at the bottom of the window can trap water rather than keep it out.

Step 3: Check the glazing seal

The glazing seal is where the glass meets the sash. On older wood windows, that is glazing putty. The National Park Service says glazing putty should be checked for cracked, loose or missing sections, which let water soak the wood, especially at the joints ⁶. The brief treats reglazing, removing the old putty and setting new, as part of routine wood window repair ⁶.

Factory-made windows usually seat the glass with gaskets or sealant rather than putty. If that seal has a gap, check the window's warranty before anyone works on it. Fogging between the panes is a different failure, explained in foggy window between panes.

Step 4: Check the frame joints and exterior caulk

Look at the corners of the frame and where the frame meets the siding or trim. The National Park Service says windows should be inspected for water entering around the edges of the frame, and those joints caulked ⁶. ProVia's guide says to inspect exterior caulking regularly and replace it when needed, and its warranty treats caulking as the owner's maintenance, not part of the window ³.

Caulk has limits. It is the visible outer line, not the main barrier. Andersen's installation article says sealant should never be used as a waterproofing detail ⁴, and another Andersen article notes that sealants and tapes work until they do not ⁵. Caulking the outside of the frame joints is reasonable upkeep; caulking over a leak whose source you have not found can hide it. Caulk around windows explains where caulk goes and where it should not.

Step 5: Consider the sill and the flashing

If the drainage works, the glazing is sound and the caulk is intact, and water still appears, the problem is probably behind the window. Windows interrupt the wall's water barrier, and the Building America Solution Center says many homes suffer water intrusion around windows, often unnoticed until damage inside the wall is extensive ². It says flashing is laid in overlapping layers so water sheds outward: a pan at the sill, side flashing over the pan, and head flashing over the sides, all tied into the wall's drainage layer ².

When that sequence is wrong, water goes behind the wall. Andersen describes a job with no head flashing that relied on a caulked casing, where water got behind the stucco and led to rotted sheathing and framing, moldy insulation and damaged drywall ⁴. Another Andersen article calls a missing head flashing one of the most overlooked details its author sees ⁵.

A homeowner cannot see flashing without removing trim or siding. Signs that point to it:

• Water on the wall below the window, or stains spreading from the lower corners.
• Soft or discolored wood at the sill or the framing below it; see rotted window frame: repair or replace.
• A leak that began soon after new windows went in.

Installation defect or wear?

A leak in a window installed within the last few years, coming from behind the frame, is often an installation question. A manufacturer warranty may exclude it: ProVia's warranty excludes damage resulting from improper installation ³. The installer's own workmanship warranty is the one to read. Window warranties explained covers the difference, and how are replacement windows installed shows what correct flashing looks like.

On an older window, a leak is more often wear: failed putty, cracked caulk, blocked drainage or rot. Those can often be repaired. When the frame is soft, the sash is failing, or the leak is from flashing that can only be redone with the window out, replacement may make more sense. Repair or replace windows walks through that decision.

What repairs cost

Fixr's window repair guide (updated January 21, 2026) gives these ranges ⁷:

Fixr notes that a leak that has gone on for a while can add water damage, mold remediation and insulation replacement to the bill ⁷, which is why hidden damage found when trim comes off can move a quote. More repair figures are in window repair cost. For drafts rather than water, see drafty windows: what to try first.

Before you call anyone

Write down where the water appears, in what weather, and since when. Run the weep-hole test and photograph the result. Then ask each company how it will find the source before it quotes a fix, whether it will open the trim to check the flashing, and what its workmanship warranty covers. Is the installer licensed in your state? If replacement is the answer, you can compare quotes from window installers.

We are not affiliated with the manufacturers named.

About these figures

• ¹ Official record: DOE Building America Solution Center guide to weep holes: what they are, the water test, cleaning steps and the risk of caulking them over, checked October 27, 2026.
• ² Official record: DOE Building America Solution Center guide to window flashing: water intrusion around windows and the pan, side and head flashing sequence, checked October 27, 2026.
• ³ Reported: ProVia care and warranty card: water in the sill area by design, keeping weep holes clear, exterior caulking as owner maintenance and the improper-installation exclusion, checked October 27, 2026.
• ⁴ Reported: Andersen article on a failed installation: missing head flashing, sealant not a waterproofing detail, bottom flange drainage and resulting damage, checked October 27, 2026.
• ⁵ Reported: Andersen article on installation mistakes: missing head flashing and the limits of sealants and tapes, checked October 27, 2026.
• ⁶ Official record: National Park Service Preservation Brief 9 on inspecting glazing putty and frame joints for water entry and on reglazing as routine repair, checked October 27, 2026.
• ⁷ Reported: Fixr window repair ranges for leaks ($50 to $600), resealing ($50 to $400), flashing ($250 to $600) and water damage ($150 to $1,000), and the added costs of an ongoing leak, updated January 21, 2026, checked October 27, 2026.