Windows drafty, foggy, or leaking
easy 1–2 h
Tools: incense stick or lit candle, utility knife, caulk gun, screwdriver, tape measure · Materials: exterior-grade silicone or polyurethane caulk, self-adhesive foam or V-strip weatherstripping, rope caulk for winter-only sealing, window insulation film kit
Steps
- On a windy day, hold a candle or incense near the sash edges, the frame-to-wall joint and the lock; where the flame bends, you have found the draft.
- Outside, cut out cracked caulk between the frame and the siding or brick and re-caulk with an exterior sealant; leave the weep holes at the bottom of the frame open.
- Inside, replace flattened weatherstripping on the sash with foam or V-strip, and adjust or replace a lock that no longer pulls the sash tight.
- Check the operation: a sash that drops or will not lock is a balance or hinge problem and lets air through the top gap.
- For a leaking window, look where the water enters: at the sill means the outside caulk or the sill pan; at the top means the flashing or the wall above, not the window.
- For single-pane or old double-hung windows in winter, fit shrink film inside or rope caulk around the sash and take it off in spring.
Stop and call a pro if
- the glass is fogged between the panes — the sealed unit has failed and must be replaced
- water is coming in above the window or the wall below is soft, stained or mouldy
- the frame is rotten, warped or the window will not close — that is a replacement, not a seal
What a pro does that you can't
A window contractor replaces a fogged glass unit without changing the frame, re-flashes a leaking opening, and replaces windows that are past sealing with properly flashed units.
DIY cost: $15–40 in caulk and weatherstripping; $20–40 for a film kit