In Corrimal, Woonona, Bellambi and the streets around them, mould usually starts in one of two places: under the floor of an older cottage sitting on slow-draining ground, or on the coldest wall of a newer, well-sealed townhouse. Illawarra Mould Removal passes enquiries from this strip to an independent local remediation professional, who works out which of those you have before quoting any treatment.
The climate on the flats
The Bureau of Meteorology’s Bellambi AWS station, right on this stretch of coast, records a mean annual rainfall of 1,148.5 mm with rain of at least 1 mm on about 93 days a year. Bellambi’s mean 9am relative humidity peaks at 76% in February, and February is also its wettest month at 150.5 mm on average. Being on the water, Bellambi’s winter nights are milder than inland, with a mean July minimum of 10.2°C, so the main problem here is less about cold surfaces and more about humid air and wet ground that are slow to dry.
Three patterns in the northern suburbs
Colliery-era cottages. Corrimal, Woonona and Balgownie grew around the district’s collieries, and many of the original miners’ cottages, weatherboards and interwar brick homes are still standing. They have often been renovated above the floor while the subfloor was left alone. Vents get painted shut, buried behind raised garden beds or closed in when a veranda or sunroom is built over them. Once air stops moving under the floor, ground moisture goes up into bearers, joists and the underside of the boards. The first sign is usually a smell, not a stain; our musty smell guide explains how to narrow down where it comes from.
Low ground near Towradgi Creek and Bellambi Lagoon. Much of Towradgi, Bellambi and East Corrimal sits on flat coastal plain with little natural fall. After a run of wet weather the soil can stay saturated long after the rain stops, which keeps subfloor humidity high even under houses whose vents are clear. Where an older house here also has a blocked vent, the two problems compound.
Townhouses along the Princes Highway. Older homes along the corridor have steadily been replaced by townhouses and dual occupancies. Tighter building envelopes hold the moisture from showers, cooking and clothes dried indoors, and it condenses on the coldest surface: an external bedroom wall, a wardrobe corner, an ensuite ceiling. NSW Health’s mould factsheet recommends running exhaust fans when showering, cooking and drying clothes and limiting unflued gas heaters, and that is most of the fix in a newer townhouse once any leak has been ruled out.
What gets arranged here
- Subfloor and roof void mould treatment for the older raised homes: treatment of affected timbers plus the ventilation and drainage correction that stops it coming back.
- Mould inspection and moisture investigation before treating an older home, because rising damp, a buried vent and a slow plumbing leak can look identical from the lounge room. Our rising damp vs condensation guide explains how they are told apart.
- Bathroom and ceiling mould removal for townhouse condensation, paired with a check that the exhaust fan actually vents outside.
Price depends on subfloor size and access, how much timber or lining is affected and what ventilation work is needed; the mould removal cost guide explains each factor, and the independent contractor quotes after assessment. Bulli and the villages to the north are covered on our Thirroul page; Fairy Meadow and the city are on the Wollongong page.
Frequently asked questions
Our Woonona weatherboard smells musty but we cannot see any mould. What now?
That usually points below the floorboards. Moisture readings in the subfloor show whether it is blocked ventilation, saturated ground or a leak, and treatment only makes sense once that is known.
We renovated a Corrimal cottage and mould has appeared behind the wardrobes. Why now?
New windows and draught sealing keep in moisture that used to escape, so it condenses on the coolest surfaces, such as external walls behind furniture. It means the airflow needs rebalancing, not that the renovation was faulty.
Why does mould seem worse near Towradgi Creek and Bellambi Lagoon than a few streets inland?
Flat, low ground drains slowly after rain, so soil under the house stays wet for longer and subfloor humidity has less chance to drop between wet spells. It is one factor an inspection weighs alongside the age and ventilation of the house.
Is mould in a two-year-old townhouse worth a professional look?
If it comes back after cleaning, yes. Confirming that it is condensation rather than a leak, before spending money on the wrong fix, is the point; sometimes the answer is simply an exhaust fan that vents into the roof space.