Published: 29 June 2026

Quick Answer

Window condensation in Melbourne winter happens when warm, moist indoor air hits cold glass — it’s not a fault with your windows, it’s a ventilation and humidity problem. You can fix most cases with better ventilation, a dehumidifier ($80–$300), window insulation film ($20–$60 per window), or secondary glazing ($150–$400 per window). Left untreated, condensation causes mould, rotting timber frames, and health issues — act before July deepens.

Cartoon illustration of a Melbourne home exterior in winter with heavy condensation on windows
Heavy condensation on single-glazed windows is a common Melbourne winter problem — warm indoor air hits cold glass and moisture falls out, and if left untreated it leads to mould on frames, sills, and nearby walls.

If you’ve noticed water pooling on your windowsills every morning, streaks running down glass, or a persistent damp smell near windows during winter, you’re not alone. Condensation is one of the most common complaints from Melbourne homeowners, particularly in SE suburbs like Dandenong, Narre Warren, and Cranbourne where older housing stock — built before double-glazing was standard — is common.

The good news: most condensation problems are fixable without replacing your windows. Here’s how to diagnose the cause and fix it yourself, or know when to call a professional.

Why Do Windows Get Condensation in Melbourne Winter?

Condensation forms when warm, moisture-laden air inside your home contacts a cold surface — your single-glazed window glass. Melbourne’s winters (June–August) are particularly prone to this because:

  • Indoor heating creates warm, moist air from cooking, showers, breathing, and drying laundry
  • Single-glazed windows (common in homes built before 2000) have surface temperatures as low as 4–8°C on cold mornings
  • Modern draught-sealing paradoxically traps moisture inside because fresh air can’t circulate
  • Older brick veneer homes in SE Melbourne have limited ceiling-to-floor insulation, keeping walls and frames cold
Pro tip: The dew point tells you when condensation will form. In a typical Melbourne winter living room (20°C, 60–70% relative humidity), condensation appears on any surface below 12–15°C — which is exactly where single-glazed glass sits on a cold night.
Cartoon illustration of condensation water droplets on a window frame and pooling on the timber sill
Water pooling on the windowsill is the first visible sign of heavy condensation — it means the humidity inside is high enough to rain on your glass, and the sill timber is absorbing moisture each morning.

Step 1: Identify Where the Moisture Is Coming From

Before spending money on window film or a dehumidifier, find the humidity source. Run through this checklist:

Source Contribution to Indoor Humidity Fix
Drying laundry indoors Very high — adds 2–4 litres of moisture per load Dry outdoors or use ducted dryer vented outside
Unflued gas heater High — combustion releases water vapour directly into room Use flued heater or ventilate room while running
Cooking without rangehood Moderate — boiling water adds significant moisture Run rangehood, open kitchen window while cooking
Long hot showers, no exhaust fan Moderate — each 10-minute shower adds ~0.5 litres Run exhaust fan during and 15 minutes after shower
Aquariums, indoor plants (many) Low to moderate — ongoing slow evaporation Move near windows with ventilation
Breathing and occupants Low but constant — averages 0.3L per person per hour Ventilate with trickle vents or window opening

Step 2: Improve Ventilation (Free to $150)

Open Windows Briefly in the Morning

Even 5–10 minutes of cross-ventilation in the morning flushes humid overnight air and drops the dew point significantly. Open opposite windows in the house to create a through-draft. Yes, it’s cold — but it works.

Install Trickle Vents

Trickle vents are small slots drilled into window frames or walls that allow constant low-level air exchange. They cost $15–$40 per vent at Mitre 10 or your local hardware store, and many modern aluminium window frames can have them fitted without tools. Check with the manufacturer before drilling into uPVC frames.

Use Exhaust Fans Properly

Kitchen rangehood and bathroom exhaust fans must vent outside — not into the roof cavity. Check that your exhaust fan has external ducting. Run the bathroom fan for at least 15 minutes after showering.

Pro tip: A simple digital hygrometer (around $15 from Bunnings or Total Tools) shows indoor humidity in real time. Aim for 40–55% relative humidity in winter — above 60% is where condensation and mould risk climbs sharply.

Step 3: Reduce Humidity at the Source ($80–$300)

Portable Dehumidifier

A portable compressor dehumidifier is the single most effective fix for severe condensation. It pulls moisture directly from the air before it reaches your windows. In Melbourne’s climate:

Dehumidifier Type Capacity Cost Best For
Desiccant (e.g., Ionmax ION612) 7 litres/day $180–$250 Single bedroom or small living room; works in cold rooms
Compressor (e.g., Inventor 20L) 20 litres/day $220–$380 Open plan living areas; more efficient above 15°C
Peltier (mini, no-brand) 0.5–1 litre/day $50–$90 Very small bedrooms only; not effective for whole rooms

In Melbourne’s winter, desiccant models work better than compressor types in unheated rooms (like bedrooms overnight) because compressor dehumidifiers struggle below 15°C. Run the dehumidifier in the rooms most affected — usually bedrooms and the living room.

Cartoon illustration of a homeowner emptying a portable dehumidifier water tank in a Melbourne bedroom
Emptying a portable dehumidifier — in a well-sealed Melbourne bedroom in winter, a good desiccant unit can pull 1–2 litres of moisture from the air overnight, which is moisture that would otherwise end up on your windows and sills.

Step 4: Insulate the Cold Glass Surface ($20–$400 per window)

If ventilation and humidity control aren’t enough — or if you have a rental property you can’t modify heavily — insulating the glass surface itself raises the temperature so condensation doesn’t form.

Window Insulation Film (DIY, $20–$60 per window)

Secondary glazing film is a transparent shrink-wrap film applied to the window frame with double-sided tape, then heat-shrunk flat with a hair dryer. It creates a trapped air gap that raises the inner glass surface temperature by 3–6°C. Brands include 3M Window Insulation Film Kit and Magiflex.

The film is not permanent — it can be removed at the end of winter without damaging paint. It does reduce clarity slightly but is nearly invisible on windows you don’t look through closely.

How to apply window insulation film:

  1. Clean the frame thoroughly — film won’t bond to dusty or painted surfaces
  2. Apply double-sided tape around the window frame perimeter (inside of the frame, not the glass)
  3. Cut film with 5cm clearance on each side
  4. Press film onto the tape, pulling taut to avoid creases
  5. Use a hair dryer on medium heat, moving in overlapping passes until film shrinks taut
  6. Trim excess with a box cutter

Secondary Glazing Panels ($150–$400 per window)

For a semi-permanent upgrade, secondary glazing adds a second panel inside the existing window — either a magnetic acrylic panel (like Magnetite) or a DIY aluminium-framed glass panel. These are popular in SE Melbourne rental units because they’re removable and don’t require building permits.

Pro tip: Secondary glazing also dramatically reduces noise from main roads — very useful in Dandenong and Cranbourne near the Princes Highway and train lines.

Step 5: Address Mould That Has Already Formed

If you already have mould on window frames, sills, or nearby walls, treat it before it spreads:

Surface Mould Severity Treatment Cost
Painted timber sill Surface only (black spots) White vinegar or diluted bleach (1:10), scrub, repaint with mould-resistant paint $20–$50 DIY
Aluminium frame (black staining) Surface mould in gaskets Spray with Selleys Rapid Mould Killer, wipe; replace gaskets if cracked $15–$30 DIY
Wall plaster beside window Penetrating mould (pink or black patches) Prime with Zinsser Mould Killer, repaint with Dulux Wash & Wear mould-resistant $60–$150 DIY
Timber frame (soft, black throughout) Structural rot Replace frame section — call a licensed carpenter $300–$800 professional
Wall cavity (musty smell but no visible mould) Internal mould — potential WHS issue Engage a licensed building inspector $250–$600 professional
Safety warning: If mould covers more than one square metre or has penetrated into wall cavities, don’t disturb it yourself. Mould remediation at this scale can release mycotoxin spores — engage a certified mould remediation specialist. This is especially important in homes with young children, elderly residents, or anyone with respiratory conditions.
Cartoon illustration of a safety expert in P2 mask and gloves cleaning mould from a window sill
Tackling mould on a windowsill — wear a P2 mask and gloves when cleaning mould, even small patches, as disturbing the spores without protection can cause respiratory irritation. Always treat and repaint with mould-resistant paint to stop regrowth.

Troubleshooting: What Your Condensation Pattern Tells You

Pattern Likely Cause Action
Only bedroom windows, every morning Breathing/occupants overnight, poor ventilation Trickle vent, crack window before bed, desiccant dehumidifier
Whole house, worst in kitchen and bathroom High humidity generation — cooking, showers, laundry Improve exhaust fans, stop drying laundry indoors, ventilate while cooking
Only north-facing windows Unlikely — check for air leak around frame allowing outside moisture in Re-seal frame with silicone; check weep holes on aluminium frames aren’t blocked
Between the glass panes (double-glazed windows) Failed IGU (insulated glass unit) — seal has broken down Call a glazier to replace the IGU — this is not DIY-fixable
Walls and ceiling, not just windows Interstitial condensation — moisture in wall cavity, or rising damp Call a building inspector — may need vapour barrier or subfloor ventilation

When to Call a Professional

DIY fixes handle most condensation problems. Call a licensed tradesperson when:

  • Double-glazed windows fog between the panes — the IGU seal has failed. A glazier replaces the glass unit (typically $200–$500 per window). You cannot fix this without replacing the sealed unit.
  • Mould appears on walls away from windows, or on ceilings — this may indicate a roof leak, failed waterproofing, or rising damp that’s unrelated to ventilation. A licensed builder or building inspector can pinpoint the source.
  • Timber window frames feel soft or spongy — structural rot has set in. A licensed carpenter must assess and replace the affected timber before mould spreads to the wall framing.
  • Your unflued gas heater is the humidity culprit — converting to a ducted or reverse-cycle system is a licensed gas fitting job in Victoria. Only a licensed gasfitter registered with Energy Safe Victoria can connect or modify gas appliances.

Top 10 Tips and Gotchas for Melbourne Window Condensation

  1. Don’t seal every draught at once without adding ventilation. Draught-sealing without trickle vents traps humidity, making condensation worse. Add passive ventilation before blocking every gap.
  2. Wipe sills daily if condensation is severe. Leaving water to sit on timber sills accelerates rot. A 30-second wipe each morning buys you time while you implement longer fixes.
  3. Reverse-cycle air conditioners also dehumidify. Running your split system in heating mode removes moisture as it heats — often more efficient than a separate dehumidifier in Melbourne’s moderate winters.
  4. Check that roof insulation isn’t blocking roof vents. Blocked roof vents reduce air exchange through the roof cavity, which pushes moisture back down through ceilings.
  5. Don’t use unflued LPG heaters for whole-home heating. Portable LPG heaters release enormous amounts of water vapour — up to 1.6 litres of moisture per kilogram of LPG burned. They’re for spot heating only.
  6. Window insulation film is renter-friendly. It peels off without damage to paint, making it ideal for rental properties in Frankston, Cranbourne, and Pakenham where landlords won’t approve permanent changes.
  7. Condensation on internal walls (not just glass) signals a bigger problem. This is interstitial condensation inside the wall cavity — get a builder to check your vapour barrier and subfloor ventilation.
  8. Mould-resistant paint is not the same as regular white paint. Standard paint will re-mould within months. Use Dulux Wash & Wear, Solver Cleanability or Taubmans Endure with added mould inhibitor for lasting protection.
  9. Check weep holes on aluminium windows. Most aluminium frames have small holes at the bottom that drain condensation away. If these are blocked with dirt or silicone, water pools inside the frame and breeds mould. Clear them with a toothpick.
  10. Measure your humidity before spending money. A $15 hygrometer from Bunnings or Mitre 10 shows whether your home is actually over 60% RH — if humidity is fine and condensation persists, the problem is the glass temperature, not the air, and insulation film is the fix.
Cartoon illustration of a safety expert holding a hygrometer showing high indoor humidity
A digital hygrometer shows 65% relative humidity — above the 55% threshold where condensation risk rises sharply on cold glass. At this level, running a dehumidifier or improving ventilation before bed will measurably reduce morning window condensation.

Local Melbourne Resources

FAQ: Window Condensation in Melbourne Winter

Is condensation on windows covered by home insurance?

Generally, no. Condensation is considered a maintenance and ventilation issue, not sudden accidental damage. However, if condensation has led to structural rot in frames or wall framing, a building defects claim may apply — check your policy with your insurer. Mould arising from a leaking roof or burst pipe (a covered event) may be claimable.

My windows fog up but then clear by mid-morning — do I still need to act?

Yes. Even if condensation evaporates by 9am, the water has been sitting on timber sills and frame joints every morning. Over a Melbourne winter of 60–90 days, that repeated wetting and drying causes timber to rot and mould to establish in joints. The clearing is just the room warming up — the nightly damage is still happening.

Does opening windows in winter actually help, or does it let in cold damp air?

It helps. Melbourne’s outdoor winter air, while cold (6–12°C), is typically drier than heavily occupied indoor air. Opening windows for 5–10 minutes flushes moisture-laden indoor air and replaces it with drier outdoor air that, once reheated indoors, holds much less relative humidity. The small heat loss is worth it — most heating systems recover within 15 minutes.

My double-glazed windows have fog between the panes — can I fix this myself?

No. Fog between the panes means the hermetic seal on the IGU (insulated glass unit) has failed, allowing moist air in. The only fix is replacing the IGU, which must be done by a glazier. The frame usually stays; only the sealed glass unit is replaced. In Melbourne, this typically costs $200–$500 per window depending on size.

Is it worth upgrading to double glazing to fix condensation in Melbourne?

For owner-occupiers planning to stay long-term: yes, for heavily affected rooms. Double glazing raises the inner glass surface temperature by 8–12°C compared to single glazing, eliminating condensation on the glass almost completely. Costs range from $600–$1,500 per window installed in Melbourne. But if budget is a constraint, window insulation film ($30–$60 per window DIY) achieves 60–70% of the thermal benefit for a fraction of the cost.

We have a bathroom with no exhaust fan — can I just open a window instead?

Opening a window during a shower helps but isn’t as effective as an exhaust fan, because bathroom fans are designed to rapidly remove moisture-laden air mechanically. If you can’t install an exhaust fan (e.g., a rental), open the window fully during the shower and leave it open for 20 minutes afterwards, and keep the bathroom door closed so moisture doesn’t migrate to the rest of the house. A battery-operated portable dehumidifier in the bathroom is also effective.