Mold on Windows From Condensation

What Condensation Is Telling You

Condensation forms when humid indoor air meets a surface cold enough to drop it below its dew point. Window glass and frames are the coldest interior surfaces in most homes, so they condense first.

That makes windows an indicator. Persistent condensation means indoor humidity is high enough that other, less visible cold surfaces — inside exterior walls, behind furniture, in closets on outside walls — may also be condensing.

Why This Happens in Katy

The regional pattern is counterintuitive. Summer here produces condensation on the outside of cold glass, which is harmless. The problem months are winter, when heated humid indoor air meets glass chilled by a cold front.

Homes that are tightly sealed but under-ventilated hold moisture from cooking, showering, and breathing. Without adequate exhaust, that moisture accumulates and finds the coldest surface available.

Fix the Humidity, Not the Window

Clean It Properly

Growth on glass, metal frames, or vinyl is surface-level and cleans up with detergent and water. Dry the area completely afterward.

The part that matters is the sill and the wall below it. If the sill is soft, discolored, or the paint is bubbling, water has been sitting long enough to get into the material and the problem is no longer cosmetic.

When It Has Gone Past the Window

Staining on the wall beneath the sill, soft drywall, or a musty smell near the window means water has entered the wall assembly. At that point it may also be a failed window seal or flashing rather than condensation.

That distinction matters — a humidity problem is solved with ventilation, while a flashing failure requires opening the wall.