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Fix a window seal that leaks

We'll locate the leak, inspect the weatherstripping and caulk, and fix or replace the seal—or tell you when to call a pro.

Troubleshooting · Home maintenance
15–45 min
What you'll need
  • Replacement weatherstripping (foam, vinyl, or rubber—match existing type)
  • Exterior-grade silicone or urethane caulk (for exterior gaps)
  • Caulk gun and putty knife (to remove old caulk)
  • Damp cloth (for cleaning)
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Steps

Goal: Confirm where the draft is, inspect the weatherstripping and caulk, and fix or replace the seal.

  • Close the window and run your hand along the sash edges, meeting rail, and frame. Feel for cold air. On a windy day, hold a lit candle or incense near the edges.
  • Good: You feel drafts—proceed to Inspect weatherstripping.
  • Bad: No drafts—you may be done. If the window leaks water or has fog between panes, that is a different problem.

Inspect weatherstripping

Goal: Check the weatherstripping condition to decide whether to reseat or replace.

  • Look at the weatherstripping where the sash meets the frame—top, sides, and bottom. Check for wear (flattened or compressed), tears, gaps at corners, or missing sections.
  • Foam and vinyl strips compress over time and lose their seal. Brittle, cracked, or pulled-away strips need replacement.
  • Good: You see worn or damaged strips—proceed to Replace weatherstripping. Loose but intact—proceed to Reseat weatherstripping.
  • Bad: Strips look fine—check Caulk around the frame.

Reseat weatherstripping

Goal: Press loose weatherstripping back into place so it seals.

  • If the strip is loose but not worn, press it back into the channel or reattach it. Foam strips with adhesive may have peeled; clean the surface and press firmly.
  • For strips in a groove, push the strip fully into the channel. If it will not stay, replace the strip.
  • Good: The weatherstripping is flush against the frame and the seal improves—done.
  • Bad: Still loose or still leaks—replace the weatherstripping.

Replace weatherstripping

Goal: Remove old weatherstripping and install new strips that seal properly.

  • Remove the old strip by pulling it from the channel or peeling adhesive-backed strips. Take a sample to a hardware store to match type and size, or measure the length and thickness.
  • Install the new strip—press adhesive-backed strips firmly; for channel strips, start at one end and work along the length. Cut to fit at corners.
  • Good: You see a continuous seal with no gaps. Test for drafts—you should feel none.
  • Bad: Still leaks—check caulk around the frame.

Recaulk the frame

Goal: Seal gaps where the window frame meets the wall.

  • Check the caulk where the frame meets the wall—interior and exterior. Cracked, peeling, or missing caulk lets air in.
  • Scrape out old caulk with a putty knife. Clean the surface with rubbing alcohol and let it dry.
  • Apply a continuous bead of caulk—interior-grade for inside, exterior-grade silicone or urethane for outside. Tool the bead with a wet finger or caulk tool for a smooth seal.
  • Good: You see no gaps and a clean, continuous seal. Test for drafts—you should feel none.
  • Bad: Still leaks—call a window professional.

When to get help

Call a window professional if:

  • The window is on an upper floor and requires a ladder.
  • The frame is warped or damaged.
  • You have replaced the weatherstripping and recaulked but it still leaks.
  • The window is a large picture or commercial unit.

For related fixes, see Fix a window that leaks, Fix a door weatherstrip that leaks, Fix a window that sticks, or Fix a window that has fog between panes.

Verification

  • No drafts when you run your hand along the window perimeter.
  • Weatherstripping is continuous with no gaps at corners or joints.
  • Caulk around the frame is continuous with no cracks or gaps.
  • The window closes and the seal compresses properly.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm symptom Locate where drafts enter—sash edges, frame, or meeting rail.
  2. Inspect weatherstripping Check for wear, compression, tears, or gaps.
  3. Clean and reseat Clean the surface; reseat loose weatherstripping.
  4. Replace weatherstripping and recaulk Remove old strip; install new weatherstripping; recaulk gaps.
  5. Call a pro High windows, damaged frame, or repeated failures—call a window professional.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Where the leak occurs (top, bottom, sides, meeting rail)
  • Condition of weatherstripping (worn, torn, missing)
  • Condition of caulk around the frame
  • Steps already tried

Do you feel drafts at the window?

Run your hand along the sash edges, meeting rail, and frame when the window is closed. On a windy day, hold a lit candle or incense near the edges.

Close the window. Run your hand along the perimeter. Yes: You feel drafts—proceed to inspect weatherstripping. No: If no drafts, you may be done. If unsure, test on a windy day.

Yes No

You can change your answer later.

Is the weatherstripping worn, torn, or missing?

Check the weatherstripping around the sash. Worn or compressed strips no longer seal. Tears and gaps let air in.

Look at the weatherstripping on top, sides, and bottom of the sash. Worn or damaged: Replace the strip. Loose but intact: Reseat it. Good: Strip looks fine—check caulk around the frame.

Yes No

You can change your answer later.

Replace weatherstripping

Remove the old strip. Take a sample to a hardware store or measure length and thickness. Install new weatherstripping that matches the type. Press adhesive-backed strips firmly; for channel strips, work along the length. Cut to fit at corners. Test the seal.

Done

Is the weatherstripping loose or is the caulk cracked?

Loose strips can be reseated. Cracked or missing caulk around the frame lets air in.

If the strip is loose, press it back into the channel or reattach it. If the caulk around the frame is cracked or missing, scrape out the old caulk and apply new caulk. Good: Seal improves—done. Bad: Still leaks—replace weatherstripping or call a pro.

Yes No

You can change your answer later.

Check caulk around the frame

Cracked or missing caulk where the frame meets the wall lets air in.

Inspect the caulk where the frame meets the wall—interior and exterior. If cracked or missing, scrape out old caulk and apply new. Good: Seal improves—done. Bad: Still leaks or window is high—call a window professional.

Yes No

You can change your answer later.

Seal is fixed

No drafts at the window. The weatherstripping and caulk seal properly. No further action needed.

Done

No action needed or different problem

If no drafts, you are done. If the window leaks water, sticks, or has fog between panes, see the relevant guide.

Done

Call a window professional

Call a window professional if: the window is on an upper floor and requires a ladder; the frame is warped or damaged; you have replaced the weatherstripping and recaulked but it still leaks; or the window is a large picture or commercial unit.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why does a window seal leak air or drafts?
Common causes: worn or compressed weatherstripping that no longer seals, torn or missing strips, cracked or missing caulk around the frame, or gaps at the meeting rail. Check the weatherstripping and caulk first.
Can I fix window seal leaks myself?
Yes. Most leaks are fixed by cleaning, reseating, or replacing the weatherstripping and recaulking gaps. You can buy foam, vinyl, or rubber weatherstripping at hardware stores. If the window is high or the frame is damaged, call a pro.
When should I call a pro for window seal leaks?
Call a window professional if the window is on an upper floor and requires a ladder, the frame is warped or damaged, you have replaced the weatherstripping and recaulked but it still leaks, or the window is a large picture or commercial unit.

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