How to Stop Window Condensation and Mold on Sills

Condensation forms on windows when warm, moist indoor air meets cold glass. Over time, this moisture can cause mold on window sills and frames. Here's how to clean it up and prevent it.

Why Windows Get Condensation

• High indoor humidity from cooking, showers and drying clothes
• Poor ventilation
• Cold outside temperatures
• Single-pane or older windows

How to Clean Mold on Sills

1. Wear gloves and open the window for ventilation.
2. Wipe away moisture with a towel.
3. Clean the mold with a mold and mildew cleaner suitable for the surface, following the label. On painted sills, a little dish soap and water can remove light mildew.
4. Dry the area completely.

If mold keeps returning or covers a large area, have the window checked for leaks.

How to Prevent Condensation

• Lower humidity: Aim for 30–50% indoor humidity. Use a dehumidifier.
• Ventilate: Run exhaust fans when cooking and showering.
• Open curtains and blinds during the day so air can reach the glass.
• Open windows briefly each day to let moist air out.
• Dry clothes outdoors or in a vented dryer.
• Use window insulation film on older windows.

Wipe Daily in Winter

Keep a microfiber cloth near the window and wipe condensation every morning.

FAQ

Is condensation between double-pane glass a problem? Yes. It usually means the window seal has failed, and the window may need repair or replacement.

Can plants cause condensation? Many houseplants add moisture to the air. Move them away from windows if condensation is a problem.