Drafty Windows: Causes and Fixes

Common causes

• Worn or missing weatherstripping around the sash.
• A sash that does not lock tightly or is out of alignment.
• Cracked or missing caulk or trim seals around the frame.
• Gaps in insulation between the window frame and the wall framing.
• Single-pane glass or failed double-pane seals (cold glass can feel like a draft).

What you can safely check

• On a windy day, hold a lit incense stick or a thin strip of tissue near the edges of the sash and frame. Watch where it flutters.
• Make sure the window is fully closed and locked; locks pull the sashes together.
• Look for cracked caulk outside and gaps under interior trim.
• Check for fog between the panes (foggy windows).

Fixes to try first

• Replace weatherstripping on the sash.
• Re-caulk exterior gaps around the frame with exterior-grade sealant.
• Add low-expansion foam made for windows under the interior trim (it is meant for this; regular foam can bow frames).
• Use removable window film kits for winter as a temporary fix.

When to call a pro

If drafts continue after weatherstripping, frames are soft or rotted, sashes will not stay up, or several windows are drafty, have a window pro evaluate repair versus replacement. See the cost to replace 10 windows.