Homeowner symptom guide · Melbourne
Condensation on Windows: Why It Happens & What to Do
Condensation forming on the inside surface of windows is a very common experience in Melbourne homes during winter — but it ranges from a normal, manageable occurrence to a sign of excessive indoor humidity that can cause mould, timber damage, and health issues. Understanding the cause helps determine the right response.
Take the free home risk check →Common Causes
- • Single glazing with cold exterior: single-glazed windows have surface temperatures close to outdoor air temperature. Warm, humid indoor air contacting this cold surface cools below its dew point and condenses. This is normal physics in Melbourne winters.
- • Insufficient ventilation: modern homes sealed for energy efficiency retain more moisture from cooking, showering, breathing, and drying laundry. Without adequate ventilation to exhaust this moisture, indoor humidity rises until condensation occurs on any cool surface.
- • Unflued gas heating: gas heaters that exhaust combustion products inside the home (LPG bayonet heaters, some older ducted systems) produce significant water vapour as a combustion byproduct, dramatically increasing indoor humidity.
- • Double-glazed unit seal failure: condensation between the glass panes of a double-glazed unit (fogging inside the unit) indicates the hermetic seal has failed, the desiccant has been exhausted, and the insulating properties of the unit are significantly reduced.
When to Be Concerned
- Condensation is consistently so heavy that it runs down the glass and pools on the window sill
- You can see mould growth on window reveals, sills, or wall areas adjacent to windows
- Condensation is forming inside double-glazed units (between panes)
- Condensation appears on walls as well as windows — indicates very high indoor humidity
What to Do
- 1 Increase ventilation: run the exhaust fan in bathrooms and the kitchen range hood when cooking and for at least 10 minutes after finishing. Open windows briefly in the morning to exchange moist overnight air.
- 2 Switch heater type: replace unflued gas heaters with reverse cycle air conditioning or flued gas systems that exhaust combustion products outside.
- 3 Use a hygrometer to measure indoor humidity — target 40–60% relative humidity in living areas. Consistent readings above 70% indicate a ventilation problem.
- 4 For double-glazed unit fogging (between panes): the affected unit must be replaced — the seal cannot be repaired.
Frequently Asked Questions
-
Does condensation on windows mean my home has a damp problem?
Not necessarily — condensation on single-glazed windows in winter is very common in Melbourne homes and is primarily a function of indoor-outdoor temperature difference and humidity, not a structural damp problem. However, if it's severe, persistent, or accompanied by mould on walls, a ventilation assessment is warranted.
-
Does window film or secondary glazing reduce condensation?
Yes — both raise the inner glass surface temperature, reducing condensation. Insulating film can significantly reduce, though not eliminate, condensation on single-glazed windows. Addressing excessive indoor humidity through ventilation is still the most effective long-term approach.
See how your whole home scores — free
Answer 32 plain-English questions about your home and get an instant risk score across 8 categories.
Start the free home check →