Why Is There Condensation Inside My Windows?

First determine where the moisture actually is. Condensation on the room-facing surface is different from moisture trapped between panes.

Interior surface condensation

Indoor air contains moisture. When humid air contacts sufficiently cold glass, water can condense on the surface.

Between the panes

Moisture trapped inside an insulated glass unit may mean the sealed assembly is no longer performing as intended. Surface cleaning won't remove moisture sealed between panes.

Exterior condensation

Moisture on the outdoor surface can happen under certain weather conditions and doesn't necessarily indicate a problem with the window.

What should I do about recurring interior condensation?

Use bathroom exhaust ventilation, use kitchen ventilation where appropriate, review indoor humidity, and wipe up water that collects on trim or sills.

When does the window need attention?

Investigate further when:

• Moisture remains between panes.
• Trim is deteriorating.
• Water appears during rain.
• Mold repeatedly grows around the opening.
• The window is also drafty or damaged.

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