What to know
- Room-side condensation forms when moist indoor air meets a cold surface.
- Moisture between panes usually indicates a failed insulating-glass seal.
- Brief exterior condensation can occur on efficient glass and is not the same as indoor moisture.
- Persistent water, staining or mould needs prompt investigation rather than cosmetic cleanup alone.
First, locate the moisture
Condensation on the room side often appears during cold weather because warm, humid indoor air reaches glass or frames below its dew point. The risk rises as outdoor temperature falls or indoor humidity rises.
Moisture between panes means the sealed insulating-glass unit has likely lost its seal. That is a glass-unit repair question, not something indoor ventilation will correct. Exterior condensation near sunrise can occur on high-performance low-emissivity glass because the outer surface stays cooler; it may disappear as conditions change.
Reduce indoor moisture and improve airflow
Natural Resources Canada recommends controlling moisture sources and maintaining air circulation near windows. Use kitchen and bathroom exhaust during moisture-producing activities, make sure dryers vent outdoors, and keep heating outlets and the lower glass edge from being blocked by heavy coverings or deep objects.
A portable humidity reading can help you see patterns, but there is no single ideal indoor humidity for every outdoor temperature and house. If water repeatedly accumulates, reduce moisture production and investigate ventilation rather than relying on wiping alone.
When the window may be part of the problem
Higher-performance windows can keep interior surfaces warmer. Features associated with improved resistance include triple glazing, low-emissivity coatings, insulating gas, thermally improved spacers, insulated frames and better airtightness.
New windows are not a cure for every moisture issue. The home works as a system: air sealing without adequate ventilation can change indoor humidity. A qualified professional should investigate widespread condensation, musty odours, staining or deterioration.
Treat mould and leaks seriously
CMHC notes that mould requires moisture to grow and that water may come from indoor activities or leaks. Fixing the moisture source is essential. If the affected area is extensive, keeps returning or involves hidden materials, seek trained help rather than disturbing it yourself.
Sources and further reading
This article provides general information, not building, health, financial or rebate advice. Verify requirements for your home, jurisdiction and program before proceeding.