Draft Coming From Windows — Find & Fix It

The most overlooked truth: most window drafts don't actually come through the glass — they come from the gap between the frame and the wall, or through failed weatherstripping around the sash. Sealing the wrong spot is the #1 DIY mistake here.

Step 1 — Locate the Draft Precisely

1. On a cold or windy day, hold a lit incense stick or a thin strip of tissue near the window edges. Watch for the smoke or paper to deflect.
2. Check these zones in order: sash meeting rail (where upper and lower sash meet), sash sides (between sash and frame), frame-to-wall junction (inside trim), and the exterior casing (outside, caulk line).
3. Feel for cold air with a wet hand — it amplifies temperature differences.

Step 2 — Match the Fix to the Source

• Around the sash (moving parts): Replace or add weatherstripping foam tape or V-strip. This is the most common fix and costs under $10.
• Between frame and wall (static gap): Use a foam backer rod to fill the gap, then seal with paintable caulk. Do NOT use expanding foam on operable windows — it can bind the frame.
• Exterior caulk line cracked: Scrape old caulk, apply exterior silicone caulk rated for -40°C (important in Canada).
• Single-pane or old glass radiating cold: Add interior window insulation film — creates a dead-air buffer, can reduce heat loss by 30–40%.

Step 3 — Temporary / Emergency Fix (Tonight)

1. Press rope caulk into the sash gap — it's removable in spring, no damage, works immediately.
2. Hang a thermal curtain over the window — stops radiant cold and convective drafts from reaching the room.

When to Call a Pro

If the window frame itself is rotted, warped, or the gap exceeds 6mm around the entire frame, you're looking at a window replacement — not a patch job. Continuing to seal over structural failure wastes time and money.

Pro tip: In Canadian winters, interior window film + V-strip weatherstripping is the highest ROI combination you can do in under an hour. The film alone can make a single-pane window perform closer to a double-pane by trapping a still-air layer — the same principle as double glazing, for about $5 per window.