Condensation on the Inside of Windows

Why the glass and not the walls

Air holds a certain amount of water vapour depending on its temperature. When warm indoor air touches a cold surface it cools locally and can no longer hold that vapour, so it condenses. Window glass is almost always the coldest interior surface in a room, which makes it the first place the problem becomes visible. The walls are doing the same thing at a lower rate where you cannot see it.

Where the moisture is coming from

Showers, cooking, laundry, dishwashers, houseplants and simply breathing all add water to indoor air. Modern homes are sealed tightly, so unless it is actively removed it accumulates. A house that was fine last winter can start condensing after a bathroom fan fails or a family gets larger.

Why it matters more than the puddle suggests

Persistent condensation runs down onto sills and into frames, where it feeds mould and rots timber. On older wood windows it lifts paint and softens putty. The visible water is the least of it; the damage happens in the joint below where nobody looks until it is soft.

What actually fixes it

Ventilation and source control: run bathroom and kitchen extraction properly, vent the dryer outside, and increase air exchange. Cleaning the glass does not affect it in any way, and we would rather tell you that than sell you a service that will not change the outcome.