When a significant storm hits the Illawarra, an east coast low, an intense westerly squall off the Escarpment, or a summer electrical storm, the mould clock starts ticking the moment water enters your home. Wollongong and the Illawarra receive some of NSW’s highest rainfall intensities: the Escarpment zone at Bulli, Thirroul, and Helensburgh regularly records more than 1,800mm annually, and single storm events can dump 100mm in under 24 hours. The time between water entry and mould colonisation is 24-48 hours under ideal conditions, and in a warm, humid Illawarra summer, conditions are often ideal. This guide tells you exactly what to do, in order, in the first 72 hours. See our east coast low response plan for the broader strategic response.
Quick Answer (BLUF)
Act within 24 hours of any storm water entry. The priority order is: stop water entry, extract standing water, remove wet porous materials, begin drying with ventilation and dehumidification, and document everything for insurance. Don’t wait until water has dried naturally, by then mould has started.
Hour 0-6: Stop the Water Entry
Before you can address the moisture inside, you need to stop more coming in.
Temporary roof repairs: If a roof tile has blown off or a ridge cap has failed, a tarpaulin over the roof section provides temporary protection while you wait for a licensed roofer. Weighted down with sandbags or secured under battens at the ridge. This is emergency triage, get a roofer out as soon as possible for a proper repair.
Window and door sealing: If a window frame has failed or a door seal has blown, temporary foam tape or weatherstrip in the frame can reduce ongoing ingress until repair.
Gutter clearance: After the rain stops, clear any gutters and downpipes of debris (leaves, twigs) that may have blocked during the storm. A blocked gutter can cause water to back up under the fascia and into the ceiling space, this can continue leaking hours after rain stops. See our guide to blocked gutters, fascia overflow and top-corner mould for how to spot this specific pattern and what to do about it.
Check the subfloor: If you have a raised-floor home in a low-lying Illawarra area (Warrawong, Berkeley, Albion Park), check the subfloor via the access hatch. Standing water in the subfloor after a storm is common and needs to be pumped out immediately.
Hours 6-24: Extract Water and Remove Wet Porous Materials
Once water entry is stopped, focus on what is already inside.
Extract standing water: If you have any significant accumulation (puddles, pooling), use a wet-dry vacuum to extract it. Water that sits on hard floors and begins wicking into the subfloor or into the base of wall plasterboard extends the moisture damage zone with every hour it remains.
Remove wet porous materials:
- Lift and remove wet carpet and underlay, these cannot be dried in place effectively in the Illawarra’s humidity and represent the fastest mould substrate in a flooded room. Seal in bags and remove from the building.
- Remove soaked curtains, fabric, cushions, and rugs from the affected area, take them outside to dry in sun and wind, or to a laundromat
- Move furniture away from any damp wall areas to allow airflow
Do not use a leaf blower or fan that recirculates air without exhausting to outside: This spreads moisture around the room rather than removing it.
Hours 24-48: Begin Active Drying
The drying phase is the most critical for mould prevention. The goal is to reduce the moisture content of all affected building materials to below the mould threshold (approximately 16% for plasterboard, 19% for timber) before mould has time to establish.
Open windows and doors if outdoor conditions allow: On a sunny, low-humidity day (below 60% RH outside), cross-ventilation is highly effective. In the Illawarra after a summer storm when outdoor humidity is 80%+, opening windows into humid air is counterproductive. Check the outdoor conditions before ventilating.
Run a dehumidifier: A portable dehumidifier should be running continuously in affected areas. For a typical Illawarra storm-affected room, a 20-30L/day dehumidifier is appropriate. Empty the tank regularly (it will fill quickly). The dehumidifier works regardless of outdoor humidity, it extracts moisture from the indoor air and collects it.
Use fans in conjunction: Fans (pointing across wet surfaces, not at the wall) increase evaporation rate. Used with a dehumidifier running simultaneously, they accelerate drying significantly.
Monitor with a moisture meter: If you have one, take daily moisture readings at the base of walls and in the floor near the water entry point. You need to see readings decreasing toward the 14-16% target range.
Hours 48-72: Assess and Treat Any Surface Mould
By 48 hours after a significant water event, inspect all affected surfaces closely for early mould growth. In warm, humid conditions, surface mould can be visible within 24 hours, small grey-green or white spots on plasterboard, paint, or timber.
If surface mould is already visible: Apply an antifungal spray or solution (quaternary ammonium or hydrogen peroxide-based) to the affected surfaces, dwell for 10-15 minutes, and wipe. HEPA vacuum the area before applying anything, loose spores should be captured, not spread.
If the water was from a stormwater or drainage overflow (potentially Category 3): Apply a biocidal disinfectant to all surfaces that the water contacted, regardless of whether visible mould is present. The pathogen and nutrient load in floodwater requires disinfection. See our Category 3 water damage guide.
Document, document, document: Photograph everything, water staining, extent of wet areas, any visible mould, with date and time stamps. This documentation is essential for insurance claims. Also note the SES or Bureau of Meteorology storm records for the event date, this can support your claim timeline.
When to Call a Professional
Call a professional mould remediator immediately, don’t wait for the 72-hour assessment, when:
- Any household member has respiratory illness, asthma, or a compromised immune system
- The water entry has been significant (major roof failure, substantial flooding)
- The water source is sewage, floodwater from a waterway, or unknown origin
- You cannot get moisture readings down despite drying equipment
- Mould is already visible within 24-48 hours and is spreading
Contact us for storm-damage guidance; if a contractor is confirmed for your area, urgency is flagged to them as part of your enquiry.
FAQs
Can I stay in my home while it dries after storm damage?
For clean water entry (roof leak, rain through a window) with modest water volumes, staying in other areas of the home is generally safe during the drying phase. If there is sewage backup or floodwater involved, temporarily relocate until the affected area is professionally assessed and treated.
My walls look dry but still smell musty. Is there mould?
A musty smell after a storm event is a reliable indicator that mould growth has begun, even if visible growth is not yet apparent. Mould can be colonising the rear face of plasterboard, inside wall cavities, or in insulation without being visible on the face of the wall. A professional moisture assessment is warranted.
Does storm damage mould void my insurance if I don’t act fast enough?
Your home insurance policy typically requires you to take reasonable steps to minimise damage after an insured event. Failure to take appropriate action can be cited by the insurer as contributory failure to mitigate, potentially reducing or voiding your claim. Acting promptly and documenting your actions protects your claim.
What about a leak we can’t see, like a slow weep inside a wall rather than a storm or a burst pipe?
The timeline is different because there’s usually no obvious event to start the clock. A slow pipe weep inside a wall cavity or under a slab can run for weeks or months before a water bill, a warm patch on the floor or a musty smell gives it away, well past the 72-hour window that applies to a storm or a sudden burst. Our guide to finding a hidden pipe leak before mould does covers the early warning signs and what to do once one is found.
Storms aside, we’ve had a slow appliance leak behind the dishwasher. Does the same 72-hour logic apply?
Broadly, yes, though the discovery point is usually much later than with a storm, since an appliance leak often runs quietly behind cabinetry for weeks before anyone notices. Once found, the same priority order applies: stop the source, assess how far the water travelled, and dry or remove affected material quickly. Our guide to dishwasher and washing machine leak mould covers what’s specific to that kitchen and laundry cavity scenario.
What about a hot water system that’s burst or been slowly weeping?
The same 72-hour window applies, but the risk profile is slightly different again. A sudden tank burst is usually noticed straight away, so the response window starts on time; a slow weep from a corroding tank or a failed relief valve can run for days before anyone finds it, often in a garage, external cupboard or laundry alcove that isn’t checked daily. Our guide to hot water system leak mould covers both failure modes and what a proper response involves.
Does this 72-hour logic still apply after a house fire, given the water comes from firefighting rather than a leak or a storm?
The same underlying clock applies, but the practical response is often slower, through no fault of the homeowner. Firefighting water can soak a much larger area than a typical leak, and access is frequently delayed while safety checks, fire investigation and insurance assessment are completed, which means mould has often had longer to establish by the time drying can properly start. Our guide to mould after a house fire covers why that delay matters and what a proper response looks like once it’s safe to begin.