Fix a Drafty Window Frame and Reclaim Your Comfort

Diagnose Where the Draft Is Coming From

Before you grab the caulk gun, take time to find the real source of the draft. That way you’re fixing the right problem, not just covering it up.

Start by closing the window and running your hand slowly around the frame, sash edges, and even where the trim meets the wall. Move inch by inch and pay attention to temperature changes or moving air. On a windy day or in winter, this is especially easy to feel.

For a more precise test, hold a lit incense stick, a candle, or a thin strip of toilet paper near the frame. Move it slowly along the perimeter. If the flame flickers or the smoke/strip is pulled in one direction, you’ve found an air leak. Check these common trouble spots: where the interior trim meets the wall, where the window sash meets the frame, chipped or missing exterior caulk, and gaps at the window stool (the interior “sill” piece).

Write down or lightly mark the drafty areas with painter’s tape. If the window is loose, hard to latch, or visibly out of square, you may have a framing or hardware issue that this repair can improve—but not completely solve. In that case, this project will still reduce drafts, even if the window eventually needs replacement.

Step 1: Prepare the Window Area

Good preparation makes the repair cleaner, longer‑lasting, and easier to finish nicely.

Clear the area around the window so you have room to work—move furniture a few feet back and remove blinds, curtains, or trim pieces that are in your way. Lay down a drop cloth or an old sheet to catch dust, old caulk, and paint chips. If the window is high or wide, set up a stable step stool or small ladder instead of overstretching.

Clean the interior frame, sash edges, and trim with a mild cleaner and a rag. Remove dirt, cobwebs, and any loose paint flakes. On the outside, brush away debris and loose material using a stiff brush. The goal is to create a solid, clean surface where new caulk and foam can bond well.

Inspect existing caulk (inside and outside). If it’s cracked, separated, moldy, or pulling away, plan to remove it where you’ll be sealing. Use a utility knife or caulk removal tool to carefully cut along the edges of the old bead and peel it away. Don’t dig aggressively into the siding or window frame—just remove what’s obviously loose or failing. After removal, wipe the area with a damp cloth and let it dry completely before sealing.

Step 2: Seal Interior Gaps Around the Trim

Most interior drafts around window frames come from gaps between the trim and the wall. Sealing these with paintable caulk is one of the quickest, most effective fixes.

Choose a high‑quality, paintable acrylic latex caulk (often labeled “for doors and windows” or “for trim”). Load it into a caulk gun and cut the tip at a 45‑degree angle to create a small opening—start smaller than you think you need; you can always cut more off if necessary.

Hold the gun at that same 45‑degree angle and apply steady pressure on the trigger as you pull the tip along the gap where the trim meets the wall. Move slowly enough to lay down a continuous bead but not so slowly that it piles up. It’s better to do two light passes than one thick, messy one.

Immediately after applying a bead (don’t wait more than a minute or two), smooth it with a damp finger or a caulk‑smoothing tool. Press gently to push the caulk into the gap and create a neat, slightly concave line. Keep a damp rag nearby to wipe your finger or tool as you go.

Work your way around the entire window: sides, top, and bottom. If you find any visible cracks in the trim joints themselves (like at the corners), fill those too. Let the caulk cure according to the product instructions—often 30 minutes to a few hours before painting, and up to 24 hours for a full cure.

Step 3: Insulate Hidden Gaps With Low-Expansion Foam

If you feel strong drafts along the edges of the frame or behind the trim, the problem may be in the wall cavity around the window. You can improve this without tearing out the whole wall by using low‑expansion spray foam.

Carefully pry off the interior casing (trim) if needed, starting at a corner. Slide a putty knife between the trim and wall to gently separate paint and caulk, then use a flat pry bar to lift the trim away. Work slowly to avoid cracking the wood. Label the back of each piece with its location so reinstallation is simple.

With the trim removed, you’ll see the gap between the window frame and the rough opening. If it’s already filled with crumbling foam or completely empty, this is a major source of drafts. Use low‑expansion spray foam specifically designed for windows and doors—regular foam can expand too much and warp the frame.

Insert the foam nozzle into the gap and apply a light, steady bead about halfway into the depth of the cavity. The foam will expand to fill more of the space, so avoid overfilling. It’s better to make several light passes and let each one expand than to jam the space solid on the first try. Wipe off any foam that gets on the visible frame immediately, following the can’s instructions.

Allow the foam to cure fully, usually several hours. Once dry, trim any excess that protrudes past the face of the wall with a utility knife or small saw so that the trim can sit flat again. Reinstall the casing using finish nails, then recaulk around it as needed. This hidden insulation upgrade can make an immediate difference in comfort.

Step 4: Improve the Seal Where the Sash Meets the Frame

If the air is coming through where the movable part of the window (the sash) meets the frame, your weatherstripping may be worn, missing, or never installed properly in the first place.

Open the window and inspect the sides, top, and bottom of the sash. Look for old felt strips, vinyl seals, or rubber gaskets that are flattened, torn, or missing sections. Also check the meeting rail (where the two sashes touch on a double‑hung window) and the bottom rail where it meets the sill.

For a quick, renter‑friendly fix, you can use adhesive foam weatherstripping. Clean the surfaces thoroughly and let them dry. Cut pieces of foam to length and stick them where the sash meets the frame—usually along the sides and top for a single‑hung or double‑hung window, and along the bottom edge for a casement. Close the window gently the first time to make sure the foam compresses without preventing full closure.

For a more durable solution, consider replacing worn factory-style weatherstripping with a similar profile from a home center or the window manufacturer. This can involve sliding old strips out of grooves and pressing or tacking new ones into place. The exact method depends on your window type (wood, vinyl, or aluminum), so check installation guides or the manufacturer’s website for specifics.

Once the new seals are in place, close and lock the window. The lock often pulls the sash tighter against the weatherstripping, improving the seal. Test again for drafts with your hand or incense to confirm the improvement and adjust as needed.

Step 5: Refresh the Exterior Seal and Check Slope

The exterior side of the window is your first defense against wind and water. If the seal is failing out there, interior fixes can only do so much.

On a dry day, examine the exterior perimeter of the window where it meets the siding, brick, or stucco. Look for cracked, missing, or separated caulk; gaps between trim and cladding; or areas where paint has peeled away down to bare wood. Also look at the sill or bottom edge: it should slope slightly away from the house to shed water.

Use a utility knife or scraper to carefully remove loose or failed caulk. Brush off dust and debris, then wipe with a damp cloth and let dry. Choose an exterior‑grade window and door caulk—usually a paintable acrylic latex or a high‑quality polyurethane or silicone if the joint won’t be painted. Follow the same basic technique as indoors: steady bead, then tool it smooth.

Pay special attention to the top of the window and any horizontal ledges where water can sit. If the sill or exterior stool is flat or sloped toward the window, consider adding a small, sloped wood or PVC sill nose, or at least ensuring the caulk lines and flashing are solid so water can’t sit against the frame.

Finish by touching up bare wood or new trim pieces with a compatible exterior primer and paint. Well‑sealed and painted exterior surfaces resist moisture, which helps prevent future gaps, rot, and drafts. Once everything is dry, repeat your draft test from inside—you should feel a noticeable reduction in air movement around the window.

Conclusion

Fixing a drafty window frame doesn’t require a full replacement or a major remodel. By systematically tracking down leaks, sealing interior trim gaps, insulating hidden cavities with low‑expansion foam, upgrading weatherstripping, and renewing exterior caulk, you can dramatically improve comfort and reduce energy loss with tools most DIYers already own.

These steps are straightforward, repeatable, and scale well—once you’ve done one window, you can move through the rest of your home with confidence. Tackle the worst offenders first, test your results, and adjust materials and techniques as you go. Your home will feel more comfortable, your energy bills may drop, and you’ll have one more core repair skill ready for your next Fix Ready project.

Sources

• [U.S. Department of Energy – Air Sealing Your Home](https://www.energy.gov/energysaver/air-sealing-your-home) - Explains common air leak locations and recommended sealing methods for energy efficiency
• [EPA ENERGY STAR – Windows, Doors and Skylights](https://www.energystar.gov/products/building_products/residential_windows_doors_and_skylights) - Provides guidance on energy performance and factors that affect window efficiency
• [Fine Homebuilding – How to Replace Window Weatherstripping](https://www.finehomebuilding.com/2021/11/24/how-to-replace-window-weatherstripping) - Step‑by‑step details and illustrations for updating weatherstripping on older windows
• [Family Handyman – How to Install Spray Foam Around Windows and Doors](https://www.familyhandyman.com/project/how-to-use-expanding-foam/) - Practical tips on using low‑expansion foam safely and effectively near window frames
• [This Old House – How to Caulk Like a Pro](https://www.thisoldhouse.com/painting/21015227/how-to-caulk-like-a-pro) - Demonstrates proper caulking techniques for clean, durable joints around interior and exterior trim