Most household mould in the Illawarra comes from moisture made indoors, by showers, cooking, drying clothes and breathing, that has no easy way out, in a coastal climate where the outside air is often humid too. The prevention that works is removing that moisture at the source with exhaust fans ducted outside, adding reliable whole-house ventilation where the house is tightly sealed, and keeping wall and window surfaces warm enough not to condense. Ventilation prevents new mould; it does not remove mould that is already there.
Why coastal and newer homes struggle
Older homes leaked air; renovations and newer construction seal those gaps. The Australian Government’s YourHome ventilation and airtightness guide warns that an airtight house with inadequate ventilation may lead to condensation, mould and high indoor carbon dioxide, and that as airtightness increases so does the need for reliable ventilation. It also points out that opening windows is not reliable ventilation, because it depends on someone remembering to do it.
On the coast the outside air is often humid too, so airing alone dries a house less. Salt air also wears down silicone seals, flashings and metal fixings faster on exposed beachfront homes in places like Austinmer, Thirroul, Coledale and Kiama, opening gaps where rain gets into walls. That is a maintenance issue, but it shows up as mould.
The options, from basic to whole-house
Exhaust fans in every wet area
The foundation for every home. A fan in the bathroom, laundry and over the cooktop removes moisture where it is made, before it spreads through the house. For it to work:
- It must be ducted to the outside, not into the roof space or a wall cavity. YourHome’s condensation guide recommends venting bathroom, laundry and kitchen exhaust directly outdoors. A fan into the roof is often worse than none; see bathroom exhaust fan venting.
- It should run on after the shower or cooking stops, on a timer or humidity sensor.
- A rangehood that recirculates removes grease but returns the steam to the kitchen; one ducted outside removes both.
Continuous extract ventilation
A central fan draws air steadily from wet areas and exhausts it outside, with replacement air coming in through controlled vents or the building’s own gaps.
Positive pressure ventilation
A roof-mounted unit pushes filtered air into the house so humid air is forced out through gaps. It suits some older, leakier homes, but ask the installer how it handles damp or hot roof-space air.
Heat-recovery ventilation (HRV or ERV)
A balanced system extracts stale, humid air from wet areas and living spaces and supplies fresh outside air through a heat exchanger. YourHome describes these (mechanical ventilation heat recovery) as a total ventilation system for well-sealed homes that draws in outside air and recovers heat from outgoing humid air. An energy recovery unit (ERV) also exchanges some moisture, which can matter in a humid coastal summer when outside air is wetter than you want inside. Best suited to new builds, major renovations and well-sealed homes with recurring condensation.
Which approach suits which home
| Home | Start with |
|---|---|
| Older home, weak or missing fans | Fans in every wet area, ducted outside, with run-on timers |
| Older home with a raised timber floor | Wet-area fans plus clear subfloor vents or subfloor fans; see subfloor ventilation |
| Modern, well-sealed home with condensation | Fix any fan ducted into the roof, then consider HRV or ERV |
| Apartment with limited options | Wet-area fans, dehumidifier in problem rooms, airing habits |
| Beachfront home with mould on many surfaces | Ventilation plus dehumidifying, and a check of seals and flashings |
Habits and surfaces matter as much as equipment
- Air out by the conditions, not the calendar. Opening up helps when the air outside is drier than inside, typically on clear, cool, dry days. On muggy days or during a humid sea breeze, closing up and dehumidifying works better.
- Use a dehumidifier in closed-up bedrooms and problem rooms. See do dehumidifiers help with mould.
- Dry clothes outside where you can, and avoid unflued gas heaters, which YourHome advises against in its condensation guidance.
- Move furniture off cold external walls to let air reach them.
- Warm the cold surfaces. Ventilation removes moisture from the air; insulation, double glazing and thermally broken window frames keep surfaces above dew point, which YourHome lists alongside ventilation. Cold walls and thermal bridges are covered in cavity wall condensation.
- Check coastal seals yearly. Silicone around windows, doors, roof penetrations and skylights on exposed homes should be inspected and redone when it hardens or shrinks.
- Measure. A hygrometer in a bedroom or wardrobe shows whether a change is working.
New builds: mistakes that cause early mould
New homes in growth areas such as Calderwood, Shell Cove and West Dapto sometimes show mould within the first year or two. The usual causes:
- Construction moisture sealed in. Slabs, rain-wetted framing and wet trades release moisture; closed up too early, it ends up in the linings. A new home that smells musty is a warning sign.
- Minimum or misdirected exhaust. Fans that are undersized, switch off with the light, or duct into the ceiling; rangehoods that recirculate.
- Wet area waterproofing defects. Thin, short or uncured membranes show up as mould beside the shower or damp in the room below.
- Air leaks at service penetrations. Gaps around pipes, cables and downlights let moist air into wall and ceiling cavities.
If you are building, ask for moisture readings of framing and slab before linings go on, and consider an independent building inspector at key stages. If you find mould in a new home, notify the builder in writing with dated photos and do not let it simply be painted over. In NSW, the statutory warranty period is 6 years for major defects and 2 years for other defects for contracts signed on or after 1 February 2012, and the NSW Government lists waterproofing among examples of a major defect. This is general information, not legal advice. An independent mould inspection gives you a written record to rely on.
What ventilation will not fix
Ventilation does not kill existing mould, clean out wall cavities or roof spaces, or stop water coming in through rising damp, roof leaks or failed waterproofing. If mould is already established, deal with the source and the growth through mould remediation first, then use ventilation to stop it coming back.
Frequently asked questions
Does opening windows prevent mould in Wollongong?
It helps when the outside air is drier than inside, usually on cool, clear days. On humid days or in a damp sea breeze it can add moisture, so close up and use a dehumidifier or mechanical ventilation instead.
My bathroom fan runs but I still get mould. Why?
The usual reasons are that it vents into the ceiling rather than outside, it is too weak for the room or the duct run, it stops as soon as the light goes off, or the moisture is coming from somewhere else such as a wall cavity or subfloor. An inspection will show which.
Why does my beach house get more mould than my old inland home?
Coastal air stays humid for longer, so there is less drying capacity, and salt air wears seals and fixings faster, letting rain into walls. Consistent ventilation, dehumidifying and seal maintenance matter more on the coast.
Does a new home warranty cover mould?
Mould caused by a building defect, such as failed wet area waterproofing, may fall under the NSW statutory warranties, while mould from occupant habits generally will not. Document it, notify the builder in writing, and get independent evidence of the cause.