How to Cover Drafty Windows | Seal Leaks by Location

Cold air sneaking past window edges is a heat-loss source most homeowners can fix themselves. The trick is matching the material to the leak—weatherstripping works on sashes that move, caulk seals the frame perimeter, and a plastic film kit adds a dead-air layer over the glass.

Finding Where the Draft Actually Comes From

Before buying anything, pinpoint the leak. A candle or incense cone held near the window edge will flicker where air enters at the sash-frame interface, along the trim, or through the wall-casing gap. Three test zones cover the possibilities: the moving sash edges, the fixed trim-to-wall joint, and the glass surface.

• Movable sash gaps: air between the sashes or between the sash and frame. Weatherstripping is the fix here.
• Fixed frame-to-wall gaps: the seam where window trim meets the wall or siding. Seal these with caulk or low-expansion foam.
• Glass insulation loss: the glass feels cold but no air moves. Interior window film adds an insulating layer that stops radiant heat loss.

Weatherstripping for Moving Window Sashes

Weatherstripping seals the space where the window opens and closes. The best type depends on gap size and usage frequency. Foam tape works on double-hung windows with gaps up to about 1/4 inch. Open the window, clean the sash edge with rubbing alcohol, measure, cut adhesive-backed foam tape, press it along the bottom of the lower sash and top of the upper sash, then close. V-strip (tension seal) is better for narrower gaps. Clean the sash channel, cut V-strip to length, peel backing, and press it into the channel where the sash contacts the frame. For older windows with uneven gaps, tubular vinyl or silicone gasket strips conform better. A common mistake is applying weatherstripping to a dirty or damp surface, which kills adhesion; clean twice if needed.

Caulk and Foam for Fixed Perimeter Gaps

Gaps between the window frame and wall, or exterior trim and siding, need a permanent seal. These surfaces do not move, so caulk or low-expansion foam is correct. To caulk an exterior perimeter gap, remove old caulk and paint with a putty knife, brush away dust, then apply a continuous bead of exterior-grade caulk around the outside edge where the frame meets the siding. Smooth with a wet finger or caulk tool. On the interior, gaps between trim and wall can be filled with paintable latex caulk or backer rod pushed into deeper openings before caulking. For wider interior gaps (over 1/2 inch), low-expansion foam is more effective—spray in short bursts to avoid bulging, let cure, then trim excess. Weatherstripping belongs where movement happens; caulk belongs where things stay still.

Window Film and Quick Temporary Options

Shrink film kits add an insulating dead-air layer against the glass, especially helpful for single-pane windows in winter. Clean and dry the window frame, apply double-sided tape around the perimeter, attach the plastic sheet, then use a hair dryer to shrink it tight. Trim excess after tightening. The effect is immediate—it removes the cold-glass sensation without affecting the view. For renters or those avoiding adhesives, simpler options work. Draft stoppers placed along the base catch air under the sash; close the window over them. Heavy curtains add an insulating layer over the whole window and stop radiant heat loss, especially if they extend past edges by several inches. Our recommended curtains for drafty windows cover the best thermal fabrics. Rope caulk presses into gaps by hand, stays pliable, and peels off cleanly. These are real solutions but less effective than sealing the air leak itself. If drafts continue, the gap could be in the wall cavity behind the trim, requiring a contractor.