We clean about 120 homes a month across the Sunshine Coast, from Caloundra to Noosa. And if there’s one issue that comes up more than any other, it’s mould. Not just in winter — though that’s peak season — but throughout the year.

The Sunshine Coast’s subtropical climate delivers average humidity levels of 60-80% for most of the year. That’s above the 50-60% range where mould starts to thrive. Combine that with periods of heavy rain, limited airflow in modern construction, and the warm temperatures mould loves, and you’ve got near-perfect growing conditions.

Here’s what we’ve learned about mould prevention from actually dealing with it in hundreds of local homes.

Understanding Why the Sunshine Coast Is a Mould Hotspot

Mould needs three things to grow: moisture (relative humidity above 55%), warmth (20-35 degrees Celsius), and organic material to feed on (dust, skin cells, timber, paper, fabrics). The Sunshine Coast provides all three abundantly for 8-10 months of the year.

The Bureau of Meteorology data for Maroochydore shows average humidity above 60% in every month except August and September, and those months still hover around 55-60%. Morning humidity regularly exceeds 80% from November through April.

Modern home construction can make things worse. Energy-efficient homes are well-sealed to reduce air conditioning costs, but that sealing also traps moisture inside. Older Queenslanders with elevated floors and open verandas had natural ventilation that reduced moisture buildup. A sealed, air-conditioned home on a slab in a new Sunshine Coast estate is essentially a humidity trap.

Prevention Strategies That Actually Work

We’ve tried and observed dozens of mould prevention approaches across client homes. Here’s what consistently works.

Ventilation Is Everything

The single most effective mould prevention strategy is consistent airflow. This doesn’t mean opening windows during a humid summer rain — that’ll make things worse. It means strategic ventilation at the right times.

Exhaust fans in bathrooms and kitchens. Every shower produces roughly 1.5 litres of water vapour. That moisture needs somewhere to go. Run your bathroom exhaust fan for at least 20 minutes after showering — not just during. If your fan isn’t vented to the outside (and many cheaper installations aren’t), it’s just pushing moisture into the ceiling cavity, which creates a hidden mould problem.

Cross-ventilation on dry days. When relative humidity drops below 55% (typically on dry, sunny afternoons), open windows on opposite sides of the house to create cross-flow. Even 30 minutes of good cross-ventilation can significantly reduce indoor moisture.

Ceiling fans. Running ceiling fans on low helps circulate air and prevents moisture from settling on surfaces. This is especially important in bedrooms, where breathing produces moisture overnight. A family of four produces roughly 2-3 litres of moisture through breathing during an 8-hour sleep cycle.

Dehumidifiers — When and Where

If your home’s indoor humidity regularly exceeds 65%, a dehumidifier is worth the investment. We’ve seen them make a dramatic difference in homes with persistent mould issues.

A few practical tips from our experience:

Buy a unit rated for a larger area than your room. A dehumidifier rated for 20 square metres will work harder and less efficiently in a 20-square-metre room than a 40-square-metre unit running at lower intensity.

Place it in the most affected area first. Typically that’s the main bedroom, an internal bathroom, or a room with limited natural ventilation.

Empty the reservoir regularly, or better yet, set up continuous drainage using the hose attachment that most units include.

Running costs are reasonable — a typical household dehumidifier uses 200-500 watts, costing roughly $0.15-$0.35 per hour to run on Sunshine Coast electricity rates. Running it for 6-8 hours on humid days costs $1-3 per day, which is far less than remediation costs if mould takes hold.

Surface Management

Mould can’t grow on clean, dry surfaces. Regular cleaning removes the dust and organic matter that mould feeds on.

Wipe down wet surfaces after use. Shower screens, tiles, window sills in bathrooms. A squeegee on shower glass after each use takes 30 seconds and prevents the moisture buildup that leads to black mould in silicone joints.

Clean behind furniture. Wardrobes pushed against external walls are classic mould sites. The gap between the wardrobe and wall has no airflow, and the wall surface is often cooler (especially on south-facing walls), creating condensation. Leave at least a 50mm gap between furniture and external walls.

Address condensation on windows. Single-glazed windows in air-conditioned rooms create condensation as warm, humid outside air meets the cold glass surface. Wipe window sills daily during humid periods, and consider window film or secondary glazing for problem windows.

Products That Work

When prevention fails and you need to treat mould, not all products are equal.

White vinegar (undiluted). Spray it on, leave for an hour, wipe clean. Vinegar kills approximately 82% of mould species, according to research published in the International Journal of Environmental Research and Public Health. It’s non-toxic, cheap, and safe on most surfaces.

Clove oil solution. A quarter teaspoon of clove oil in a litre of water, sprayed on affected surfaces. Clove oil’s active ingredient, eugenol, is a powerful antifungal. This is our go-to for treating mould on painted walls and ceilings without damaging the paint.

Tea tree oil. Two teaspoons in two cups of water. Effective but expensive at scale. We reserve it for small, targeted applications.

Avoid bleach on mould. I know this is counterintuitive, but bleach is not the best choice for mould. It kills surface mould but doesn’t penetrate porous materials like grout, timber, or plasterboard. The mould roots survive and regrow. Bleach also loses effectiveness when mixed with organic matter (which is what mould is). Vinegar and clove oil penetrate better and provide longer-lasting results.

Working with cleaning technology providers like Team400 has helped our team develop data-driven approaches to tracking which prevention methods deliver the best long-term results across different home types and locations on the Coast.

When to Call a Professional

DIY mould treatment works for surface mould on tiles, glass, and painted surfaces. But some situations require professional assessment:

• Mould covering more than 1 square metre in a single area
• Mould inside wall cavities (you’ll usually smell it before you see it)
• Mould on structural timber
• Recurring mould that returns within weeks of treatment
• Any mould in homes with immunocompromised residents

For persistent mould problems, consider getting a building inspection to check for underlying moisture issues — leaking pipes, inadequate drainage, missing vapour barriers, or failed waterproofing in wet areas.

The Sunshine Coast’s climate means mould will always be a challenge. But with consistent ventilation, appropriate humidity management, and regular surface cleaning, it’s a manageable one.