Kiama and the broader South Coast, Gerringong, Gerroa, Berry, Kangaroo Valley, are among the most popular short-stay rental destinations in NSW. Owners of holiday lets in these areas face a specific set of mould challenges that differ from permanent residential properties: intermittent occupancy (which means neither regular cleaning nor consistent ventilation), high coastal humidity, basalt and sandstone construction in heritage Kiama homes, and the guest-facing cleanliness expectation that any mould discovery triggers a negative review within hours. This guide is written for holiday let owners who want a practical maintenance strategy. See our more general absentee owner guide for context, and if your holiday let sits further south again, our Nowra and Shoalhaven service coverage guide sets out the same holiday-let approach for Culburra Beach, Currarong and the wider Shoalhaven. Just south of Kiama, our guide to winter shutdown mould in Gerringong and Gerroa holiday homes covers the same intermittent-occupancy risk in more detail, with a focus on the specific danger of a closed-up property through the coldest, most humid months. The intermittent-occupancy risk that drives mould in a holiday let isn’t limited to short-stay rentals either: our guide to mould removal in Port Kembla and Warrawong covers a similar pattern in older, industrial-era housing that sits closed up or lightly used for long stretches. The same intermittent-occupancy risk applies just as directly a little further north, to the mix of full-time and weekender beach cottages covered in our guide to mould in Bulli and Thirroul.
Quick Answer (BLUF)
The biggest risk factor for mould in a holiday let is not the guests, it is the periods between bookings when windows are closed, ventilation stops, and coastal humidity builds inside the building unchecked. A systematic ventilation protocol on departure, regular inspection and treatment, and an annual preventive fogging treatment are the three most cost-effective interventions.
Why Holiday Lets Are More Vulnerable Than Owner-Occupied Homes
Intermittent Occupancy
When a property is occupied full-time, human activity, opening windows, running fans, moving air through the building, provides a degree of natural ventilation. A holiday let that is unoccupied Monday to Thursday has four days of static, stagnant air sitting inside a coastal building. In Kiama’s high-humidity microclimate (the Kiama headland and surrounding areas regularly record some of the highest coastal humidity readings in the Illawarra region), three or four unoccupied days is long enough for surface mould to establish on cool surfaces.
Inconsistent Ventilation
Guests do not ventilate the way a diligent homeowner does. They close windows against noise and leave the air conditioning running. They may not use bathroom exhaust fans. They leave damp towels in enclosed spaces and don’t air the bedroom in the morning. No criticism of guests, this is simply not their property or concern.
High Turnover Cleaning Protocols
A standard holiday let cleanout between guests focuses on surface cleanliness: vacuuming, mopping, linen, and bench tops. It does not typically include inspection of the inside of wardrobes, bathroom ceiling condition, or behind furniture, the places mould most commonly starts. By the time a cleaner notices mould, it is visible and has been growing for some time.
Kiama’s Specific Climate
Kiama sits on a basalt headland that catches both prevailing north-east sea breezes and the south-westerly weather patterns that come off the Illawarra Escarpment. The combination of direct sea exposure, basalt stone walls in many heritage properties (the town has a high concentration of 19th-century basalt construction around the CBD, blowhole area, and old residential streets), and the surrounding agricultural land that generates its own humidity means that Kiama consistently records higher relative humidity than anywhere else in the Illawarra region.
Basalt stone walls in heritage properties are highly porous and absorb moisture directly. Unlike the cavity wall construction of later buildings, these walls have no barrier against moisture ingress, and mould on interior plaster or render of a stone Kiama cottage is a direct result of moisture absorbed through the external face.
A Practical Mould Prevention Protocol for Holiday Let Owners
The Departure Ventilation Procedure
Brief your cleaner (and, via a house rules card, your guests) to follow these steps on departure:
- Open all windows and internal doors for the final 30 minutes of occupancy
- Run all bathroom exhaust fans on manual for 30 minutes before leaving
- Leave wardrobe doors ajar
- In winter, leave the heating on low (18-19°C) rather than turning it off completely, a cold, humid building is worse than a gently warmed one
After the cleaner has finished and locked up:
- Use a smart plug timer to run ceiling fans and bathroom exhaust fans for 2 hours after lockup (this is easy and inexpensive to set up with a $30 smart plug and the property’s WiFi)
Between-Booking Inspection Checklist (Weekly or Each Turnover)
Add these to your cleaner’s checklist with a photo report:
- Bathroom ceiling, any spots or discolouration
- Inside wardrobes and behind wardrobe doors
- Behind and under beds (south-facing walls in particular)
- Laundry wall and ceiling
- Under kitchen and bathroom sinks
Catching mould when it is a 10cm spot is a 15-minute job. Catching it when it is three walls of a bedroom is a $3,000+ job.
Seasonal Treatments
Pre-autumn treatment (March): As the season turns and humidity rises, schedule a professional antifungal fogging treatment. This deposits antimicrobial protection on all surfaces throughout the property and significantly delays mould establishment over the high-risk winter period.
Annual inspection (June, July): A professional mould inspection with moisture metering at the start of winter identifies any developing problems before they become visible or guest-facing.
Post-storm check: After any significant weather event, east coast lows track along the NSW coast regularly between March and June, check for any water ingress signs: damp patches, tide marks on ceilings, water under external doors.
Managing a Guest Mould Discovery
Despite best efforts, a guest may discover and report mould during a stay. Your response matters for both the guest relationship and for your ongoing platform standing (Airbnb, Stayz).
Respond promptly: Acknowledge the report immediately, apologise for the inconvenience, and commit to a resolution.
Offer appropriate remedy: Depending on the severity, a small bathroom ceiling spot vs. a bedroom wall covered in mould, this might range from an apology and an immediate cleaning visit to a partial refund or relocation.
Arrange professional treatment: After the stay, arrange professional treatment before the next booking. Do not simply re-clean and continue.
Document and fix the cause: If mould is recurring in the same location, there is a structural cause. A professional inspection should be arranged to identify and address it.
FAQs
How often should I have a holiday let professionally treated for mould?
For a Kiama or South Coast coastal property, an annual fogging treatment at the start of autumn (March-April) plus a winter inspection (June-July) is a minimum. Properties with higher occupancy or known moisture issues may benefit from a mid-year treatment as well.
Is mould in a Kiama basalt stone cottage different from mould in a modern home?
The mould species are the same, but the moisture pathway is different. Basalt absorbs and holds moisture from the external environment, and mould in stone cottages is often a result of moisture moving through the wall fabric rather than condensation or a plumbing leak. Treatment must address the surface mould and the moisture management of the wall, adding internal insulation or a vapour-permeable lime render can help.
Do I need to disclose mould history to guests or platforms?
Hosts are required by platform policies (Airbnb, Stayz) and general consumer law to accurately describe the property. Ongoing or recurring mould issues that affect habitability should be disclosed. A past mould problem that has been professionally remediated does not need to be disclosed in your listing description, but if asked directly by a guest, honest and accurate answers are advisable both legally and reputationally.
I own a weekender in the Southern Highlands rather than on the coast. Does the same intermittent-occupancy risk apply?
Yes, the same principle applies, a property that sits closed up between visits loses the ventilation benefit of daily occupancy, but the underlying mould mechanism is different. The Southern Highlands’ colder winter climate drives condensation-based mould rather than the coastal humidity covered in this guide. See our guide to mould removal in the Southern Highlands for how that cold-climate pattern plays out and what a seasonal protocol looks like for a Bowral, Moss Vale or Robertson property.