Drafty Window — Causes and Fixes

Common Symptoms

• Cold air coming through window in winter
• Window glass or frame feels cold to the touch
• Visible air movement around window frame on windy days
• Higher-than-expected heating bills
• Condensation forming on interior window frame

Most Likely Causes

1. 1

   Worn or Compressed Weatherstripping (Most Common)

   Foam, felt, or V-strip weatherstripping around the window sash compresses and hardens over years of use, eventually losing its ability to form an airtight seal when the window closes. Foam tape typically lasts 3–5 years before it flattens permanently. V-strip (tension seal) lasts longer but can crack or pull away from the channel. Worn weatherstripping is the #1 cause of window drafts and the easiest fix.

2. 2

   Failed or Missing Caulk Around the Frame

   The caulk joint between the window frame and the interior wall, and between the exterior frame and siding, cracks and shrinks over time — especially with temperature cycling. A hairline crack in exterior caulk can allow significant air infiltration on windy days. Check both the interior (where frame meets drywall or trim) and exterior (where frame meets siding or brick mold) caulk lines.

3. 3

   Crumbling Glazing Compound (Older Single-Pane Windows)

   Older wood-frame single-pane windows use a putty-like glazing compound to seal the glass pane to the frame. After 15–25 years, glazing compound dries out, cracks, and pulls away from the glass or wood, creating gaps between the glass edge and the wood sash. Wind-driven air passes directly through these gaps. This is especially common on windows with northern exposure.

4. 4

   Warped or Sagging Sash

   Wooden window sashes absorb moisture and can warp over time, creating a gap on one side of the sash even when the window is locked. A bowed sash that makes contact at the center but not the edges, or contacts on one side but not the other, will always leak air regardless of weatherstripping condition.

5. 5

   Sash Lock Not Pulling Frame Tight

   On double-hung windows, the cam-style sash lock is designed to draw the upper and lower sashes together tightly. If the lock mechanism is worn, or the sashes have shifted so the lock keeper is misaligned, the window won't close to a full seal even with new weatherstripping in place. Check lock alignment and engagement before replacing weatherstripping.

Quick DIY Checks

1. 1Step 1 — Locate the draft with a candle or incense stick: on a windy day, close all windows and doors in the room. Hold a lit candle or incense stick 1–2 inches from the window perimeter — move it slowly around the entire frame, sash perimeter, and corner joints. A flickering flame or deflected smoke stream indicates the leak location. Mark each spot with masking tape before moving to the next. This test is faster and more reliable than feeling with your hand.
2. 2Step 2 — Inspect weatherstripping for cracks or permanent compression: with the window closed, inspect the weatherstripping on all four sides of the sash. Foam tape that shows permanent grooves or compression (won't spring back when pressed) has failed. V-strip that is cracked, creased flat, or has pulled away from the channel needs replacement. Replace the entire run, not just the damaged section — piecemeal repairs create new gaps at the seams.
3. 3Step 3 — Replace foam tape or V-strip weatherstripping: for foam tape, clean the channel with rubbing alcohol and let it dry, then press new self-adhesive foam tape firmly in place. For V-strip (tension seal), cut the strip to length with scissors, fold it into a V profile, and press it into the channel or nail it with the supplied tacks at 3-inch intervals with the open side of the V facing outward toward the sash edge so it presses against the sash as it closes.

Repair vs Replace

Recommended Tools & Parts

• Foam Weatherstripping Tape (Self-Adhesive)

  Compressible foam tape with pressure-sensitive adhesive backing. Available in multiple widths and thicknesses — measure your sash channel depth before buying. EPDM foam lasts longer than standard polyurethane foam. Apply to clean, dry surfaces at temperatures above 50°F for good adhesion.

  $5–$12

  Buy on Amazon →

• V-Strip Weatherstripping (Tension Seal)

  Folded metal or plastic strip that creates a tension seal against the window sash. More durable than foam tape and better for channels where the sash slides. Available in bronze, aluminum, or plastic. Cut with scissors and nail or press-fit into the channel with the open V facing outward.

  $8–$18

  Buy on Amazon →

• Window and Door Caulk (Paintable Silicone or Latex)

  Flexible paintable caulk for sealing the joint between the window frame and interior trim or exterior siding. Use a paintable formula (not 100% silicone) for interior applications where you plan to paint. For exterior joints exposed to weather, use a siliconized acrylic or 100% silicone formula rated for exterior use.

  $5–$10 per tube

  Buy on Amazon →

• Caulk Gun

  Standard 1/10-gallon (10 oz) caulk gun for applying caulk cartridges. A ratchet-rod gun is fine for occasional use; a smooth-rod (dripless) gun gives better flow control and stops the bead cleanly when you release pressure. A basic model works for this job.

  $8–$20

  Buy on Amazon →

• Rope Caulk (Seasonal Window Sealer)

  Soft, pliable gray putty rope pressed into window frame gaps for a quick, temporary draft block. Leaves no damage or residue on window trim when removed. Works on irregular gaps where liquid caulk won't bridge. One roll typically covers 2–3 windows. Excellent emergency fix before the permanent repair.

  $4–$8 per roll

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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