How to Prevent Condensation and Mould on Windows in Melbourne Homes

Why Windows Condense in Melbourne Homes

Melbourne’s winter temperatures regularly drop to 5–8°C in the south-east suburbs, while indoor heating keeps homes at 18–22°C. The cold glass surface causes warm humid air to hit its dew point and deposit liquid water. This is a physics problem as much as a ventilation problem.

Homes most affected are:

• Built before 1990 with single-pane aluminium windows
• Homes with gas cooking, gas heating, or high occupancy
• Poorly ventilated bathrooms and laundries where moisture migrates
• Homes near wetlands in Pakenham, Officer, and Cranbourne where ambient humidity is higher

Step-by-Step: How to Prevent Window Condensation

Step 1: Measure Your Indoor Humidity

Buy a digital hygrometer (available at most hardware stores for $15–$30) and measure indoor humidity in the rooms with the worst condensation. Target: below 50% relative humidity in winter. If your readings are consistently above 60%, moisture generation in the home is the primary cause.

Step 2: Improve Ventilation

The fastest fix is more air exchange. In practice this means:

• Run exhaust fans for 20 minutes after every shower, bath, or cooking session
• Open windows 5–10 minutes per day even in winter — a brief cross-ventilation flush replaces moist indoor air
• Check exhaust fan ducting goes to outside, not into the ceiling cavity — a common fault in Melbourne townhouses built in the 2000s
• Vent your dryer outside. A vented dryer deposits 2–4 litres of water vapour per load into the air if ducted internally

Step 3: Add a Window Insulation Film

Secondary window films (available at Bunnings and hardware stores, $20–$60 per window) adhere to the inside of the glass and create a thin air gap that raises the surface temperature of the glass. When the glass is warmer, condensation reduces. These are a cost-effective first step before committing to double glazing.

Step 4: Install Secondary Glazing or Upgrade Windows

If films don’t solve the problem, the next step is secondary glazing (an acrylic or glass panel mounted inside the existing window frame, creating a double-pane effect) or full window replacement with double-glazed units. Secondary glazing costs $150–$400 per window installed vs $600–$1,500 per window for full replacement double glazing.

Step 5: Fix Mould if It’s Already Present

Window condensation creates mould on frames, sills, and surrounding walls. Clean existing mould with a 70% white vinegar solution or a mould removal spray (avoid bleach on painted surfaces — it damages the paint film without killing mould roots). For mould penetrating plaster, the affected area usually needs cutting out and replastering.

When Is Condensation Between the Panes?

If you see fogging or water droplets between the two panes of a double-glazed window, the inert gas seal has failed and the unit must be replaced. This cannot be fixed with cleaning or films. A replacement IGU (Insulated Glass Unit) costs $200–$600 per pane installed, depending on size. Most Melbourne window companies offer a repair service where only the glass unit is replaced, not the frame.

Condensation vs Mould: Understanding the Difference

Top 10 Tips and Gotchas

1. Don’t just wipe it. Wiping condensation off windows daily without fixing the cause guarantees mould will grow on the window seal and frame within weeks.
2. Gas unflued heaters are major contributors. Portable LPG or natural gas heaters burn fuel and produce water vapour — a single unit can add 1-–2 litres of moisture per hour to your indoor air.
3. Pot plants add humidity. A dozen indoor plants in a small Melbourne apartment measurably increases humidity. Move plants near windows in winter.
4. Cold corners collect mould first. External corner walls and north-facing rooms (which get less sun) are coldest. Check behind furniture in these spots.
5. Aluminium frames conduct cold. Standard aluminium window frames have no thermal break — the frame itself gets nearly as cold as the glass. Thermal break aluminium or uPVC frames solve this.
6. Silica gel dehumidifier crystals work in small enclosed spaces like wardrobes but are ineffective for whole rooms — use a powered dehumidifier instead.
7. A powered dehumidifier (35–50L/day capacity) costs $250–$500 and can transform a persistently damp bedroom in Melbourne winters.
8. Check your subfloor. Melbourne homes on piers often have damp subfloor spaces that wick moisture up through floors and contribute to indoor humidity.
9. Ventilate after cooking. Boiling 2 litres of water releases 2 litres of steam. Run the rangehood and crack a window every time you cook.
10. Safety note: If you see large-scale mould growth covering multiple walls (beyond just window frames), consult a professional mould inspector — extensive mould indicates a structural moisture problem, not just condensation.

Local Melbourne Resources

• Bunnings Insulation & Draught Proofing — window films, draught seals, and exhaust fan replacements
• Mitre 10 — hygrometers, mould removal sprays, and dehumidifiers
• Secondary Glazing Australia — DIY and professional secondary glazing solutions
• Victorian Building Authority — information on waterproofing standards and building compliance

Frequently Asked Questions