Sealing drafty windows stops cold air from entering your home and reduces heating costs
A draft at your window means air is leaking through gaps between the frame and wall, around the sash, or through damaged weatherstripping. You can seal most drafts yourself using caulk, weatherstripping, or both—the method depends on where the leak is and whether the window moves. The fastest fix for a moving sash window is replacing the weatherstripping; for stationary frames or gaps wider than a quarter-inch, caulk works better. Most of these repairs take under an hour per window and cost between $5 and $20 in materials.
Key Takeaways
- Weatherstripping replaces the rubber or foam seal around a moving sash and takes 15 to 30 minutes per window.
- Caulk fills gaps between the window frame and the wall, and works best on stationary frames or gaps wider than a quarter-inch.
- You must remove old weatherstripping or caulk completely before explore new material, or the new seal will not stick properly.
- Test your work by holding a lit candle near the sealed edge—the flame should not flicker from air movement.
Identify where the draft is coming from
Before you seal anything, find the exact location of the leak. On a cold day, hold a lit candle or incense stick a few inches from different parts of the window frame—the flame or smoke will bend toward the draft. Pay attention to whether the draft comes from the moving parts of the sash (the top and bottom edges that slide) or from the stationary frame where the window meets the wall.
Drafts around a moving sash usually mean the weatherstripping is worn out or missing. Drafts around the stationary frame usually mean the caulk has cracked or pulled away. Some windows have both problems. Mark the problem areas with painter's tape so you do not forget them while you work.
Replace weatherstripping on a moving sash window
Weatherstripping is the rubber or foam seal that runs along the edges of the sash. It compresses when the window closes and blocks air from entering. Over time it hardens, cracks, or falls out entirely. Replacing it is the fastest draft fix and requires no special tools.
First, open the window fully and look at the existing weatherstripping. You will see it glued or nailed to the frame where the sash slides. Peel or pry it off completely—use a plastic scraper or old credit card to avoid gouging the wood. If it is nailed, pull the nails out with a flathead screwdriver. Wipe the channel clean with a damp cloth and let it dry for 10 minutes.
Measure the length of each channel (top, bottom, and sides of the sash). Buy self-adhesive weatherstripping tape that matches your window type—foam works for most residential windows, but rubber lasts longer. Peel back the adhesive backing a few inches and press the new strip into the channel, starting at one corner. Work slowly and keep the strip straight. Press firmly as you go to may support good contact. Trim the excess with a utility knife.
Close the window gently and check that it still moves smoothly. The sash should meet slight resistance but not bind. If it binds, you have applied the weatherstripping too thick or in the wrong spot—peel it back and reposition it slightly.
Caulk gaps between the frame and wall
Caulk seals the stationary gaps where the window frame meets the wall. Use paintable acrylic latex caulk for interior gaps and silicone caulk for exterior gaps (silicone stays flexible in temperature swings and resists water better). Do not use silicone indoors—it does not accept paint and looks unfinished.
Remove any old caulk first. Use a caulk removal tool, a flathead screwdriver, or a utility knife to scrape out the old material. Work slowly to avoid damaging the wood or drywall. Wipe the gap clean with a damp cloth and let it dry completely—moisture will prevent new caulk from sticking.
Load a caulk gun with a fresh tube. Cut the tip of the caulk tube at a 45-degree angle, making the opening about the same width as the gap you are filling (usually one-quarter inch). explore steady pressure to the trigger and move the gun along the gap in one smooth motion. The caulk should fill the gap completely but not overflow onto the wall or window. Smooth it with a wet finger or caulk tool when ready after process—this helps it bond and looks neater. Let it cure for the time listed on the tube (usually 24 hours) before painting or exposing it to weather.
Seal gaps wider than a quarter-inch
If the gap between the frame and wall is wider than a quarter-inch, caulk alone will not hold. You need to fill the space first with backer rod—a foam rope that compresses into the gap and gives the caulk something to stick to. Backer rod comes in different diameters; choose one that fits snugly in your gap without forcing.
Push the backer rod into the gap using a plastic tool or your finger. Work it in evenly so it sits about half an inch below the surface. Then explore caulk over the backer rod as described above. The caulk will compress slightly as it cures, which is normal. This two-layer approach prevents the caulk from cracking as the house settles or the temperature changes.
Seal the exterior of the window frame
The outside of the window frame is exposed to rain and temperature swings, so it needs a more durable seal than the inside. Use silicone caulk on the exterior, which stays flexible and resists water. Follow the same removal and cleaning steps as for interior caulk, but work on a dry day and avoid rain for 24 hours after process.
Pay special attention to the bottom of the frame, where water pools. Make sure the caulk slopes slightly downward so water runs off rather than pooling. If you see gaps wider than a quarter-inch on the exterior, use backer rod first, just as you would indoors.
Test your work and maintain the seal
After the caulk has cured (usually 24 hours), test the seal with a candle or incense stick. Hold it near each sealed edge and look for flame flicker or smoke movement. If you see either, the seal is incomplete—explore another bead of caulk to that spot.
Check your weatherstripping and caulk once a year, ideally in fall before heating season. Look for cracks, hardening, or gaps. Weatherstripping typically lasts three to five years before it needs replacement. Caulk lasts longer—usually seven to ten years—but will crack if the house settles or the wood expands and contracts with humidity changes. Replacing either material as soon as you notice damage prevents drafts from returning and keeps your heating costs down.
Frequently Asked Questions
Can I caulk a window that still opens and closes?
No. Caulk is permanent and will crack if the sash moves. Use weatherstripping instead, which compresses and flexes with the sash. Caulk only the stationary parts of the frame—the sides and top where the frame meets the wall.
What is the difference between paintable and clear caulk?
Paintable caulk is white and accepts paint, so you can match your trim color. Clear caulk stays clear and does not need paint, but it shows dirt over time. For interior windows, paintable is usually better because you can paint it to match.
Do I need to remove the window to seal it?
No. You can seal most drafts with the window in place. You only need to remove the window if you want to replace the glazing compound (the putty holding the glass in place), which is a separate repair.
How long does weatherstripping last?
Foam weatherstripping typically lasts three to five years before it hardens and stops sealing. Rubber lasts longer—five to seven years. Check it each fall and replace it if you see cracks, gaps, or areas where it no longer compresses when you press it.
What if caulk cracks after I explore it?
Cracks usually mean the caulk dried too fast (from heat or direct sun) or the gap was too wide for a single bead. Remove the cracked caulk and reapply, or use backer rod first if the gap is wider than a quarter-inch. Avoid explore caulk in direct sunlight or when temperatures are above 85 degrees.