A draft at a window can come through moving sash seals, perimeter caulk, a lock that does not compress the weatherstripping, or gaps between the frame and wall. Locating the exact path matters because indiscriminate caulking can block drainage or miss the real leak.
Separate sash leakage from frame leakage
With the window closed, slowly move your hand or a light strip around the sash and frame on a windy day. Air at the moving joint points to weatherstripping; leakage between trim and wall may come from perimeter sealing.
Check lock alignment and weatherstrip compression
A loose or misaligned lock can keep the sash from compressing its seal. Clean the track, inspect weatherstripping for crushing or tears, and adjust hardware only as the window design allows.
Do not block drainage openings
Many windows have small weep openings that drain water outside. Do not plug them with caulk or foam while chasing a draft; blocked drainage can trap water in the frame.
Large frame gaps may need insulation
If air comes from behind trim or visible gaps exist between the frame and wall, insulation or air sealing may be missing. Removing finishes and working at the rough opening is more involved than replacing weatherstripping and may justify professional repair.
Sources
- U.S. Department of Energy — Energy Saver — Residential energy efficiency, heating and cooling, and equipment use.