How to Fix Drafty Windows
Drafty windows can add $200–$400 per year to energy bills. Most drafts come from failed weatherstripping around the sash, gaps in the window frame caulking, or a warped sash that no longer contacts the frame evenly. Almost all drafty window fixes are under $50 and take an afternoon.
Likely Causes
- 1Worn, compressed, or missing weatherstripping around the sash
- 2Failed or missing caulk at the window frame-to-wall joint
- 3Warped or swollen sash not closing flush to the frame
- 4Broken sash lock that doesn't draw sash tight to frame
- 5Old single-pane glass with minimal insulating value
Low urgency for safety, but each drafty window wastes money continuously. Fix before heating or cooling season.
How to Fix It: Step by Step
- 1Find the air leaks
On a cold day, hold a lit incense stick near the window perimeter. The smoke will deflect toward any air infiltration point. Common locations: sash corners, lock areas, and the joint between frame and wall.
- 2Replace weatherstripping
Remove old weatherstripping from the sash channels. Clean the channel surface. Cut new foam or V-strip weatherstripping to length and press or nail into place. The sash should compress the stripping when closed.
- 3Caulk the exterior frame joint
Apply paintable silicone caulk along the joint between the window frame and the exterior siding or brick. Tool smooth with a wet finger. Also caulk interior trim-to-wall gaps.
- 4Apply rope caulk for winter (temporary)
Rope caulk (Mortite or similar) is a soft, putty-like product you press into gaps around the sash. It's temporary, peels off in spring, and costs $3–$5 per window.
- 5Install window insulation film
Shrink-wrap window kits (3M or similar) install over the interior of the frame, creating a dead air insulation layer. Effective for single-pane windows — reduces heat loss by 25–50%.
Materials & Tools Needed
Warning Signs It's Getting Worse
- ⚠Condensation or frost on the interior glass or frame
- ⚠Window won't latch or lock
- ⚠Wood frame or sill feels soft (rot)
When to Call a Professional
Consider window replacement if the sash is visibly warped beyond what weatherstripping can compensate for, if the glass is single-pane throughout and energy bills are very high, or if the window frame itself is rotting.
Not sure where to start?
Describe your problem and get a personalized repair plan — likely causes, repair steps, materials, and cost estimates.
Get My Repair Plan