How to Make Your New Bathroom Mould-Proof: NCC Standards & Practical Tips
Why Mould Forms in Bathrooms
- Steam & humidity: Showers spike humidity; moisture settles in grout, corners and on colder surfaces, causing condensation.
- Insufficient exhaust or make-up air: Fans can’t clear steam if there’s nowhere for fresh air to enter.
- Slow drying in cool climates: Towels and surfaces stay damp longer in Ballarat, encouraging mould growth.
What the NCC Requires (Ventilation, Waterproofing)
The National Construction Code (NCC) sets the benchmark for ventilation in Australia, ensuring high-moisture areas like bathrooms stay safe and compliant. Bathrooms require 25 L/s, which can come from an exhaust fan or natural ventilation via windows. Those windows should open to at least 5% of the floor area, with a minimum of 0.15 square metres.
Mechanical Ventilation
- Minimum exhaust rate: Bathrooms and sanitary compartments: ≥ 25 L/s. Kitchens/laundries: ≥ 40 L/s.
- Discharge to outside: Exhaust MUST vent outdoors (not into a roof space).
- Make-up air matters: Undercut doors or transfer grilles help the fan actually move steam out.
Waterproofing in Wet Areas
- Showers and adjacent junctions: Must be waterproofed, and materials must be moisture-resistant per NCC wet area provisions.
The updated version of the National Construction Code takes aim at mould and moisture-damage with more stringent and detailed ventilation requirements. – Atom Lighting
Practical Tips: Design Choices & Daily Habits
During Design & Build
- Right-sized, right-ducted fan: Specify a fan that delivers ≥ 25 L/s installed and duct it directly outdoors.
- Run-on control: Add a timer or humidity sensor so the fan runs 10–20 minutes after showers.
- Make-up air: Include a discrete door undercut or transfer grille.
- Moisture-smart finishes: Use mould-resistant paints, epoxy grout; consider fewer grout lines via large-format tiles or panels.
- Encourage drying: Heated towel rails and underfloor heating speed up drying in Ballarat’s winters.
- Waterproofing: Ensure this is carried out by a licenced proofer & materials used meet NCC standards.
Everyday Habits That Work
- Vent then dry: Keep the fan running post-shower and squeegee glass/tiles to remove surface water.
- Watch humidity & temp: A small hygrometer helps keep RH roughly 50–70%; maintaining the bathroom near ~23 °C improves drying.
- Rotate textiles: Change bath towels weekly and hand towels every 2–3 days; dry them on a rail, not bunched up.
- Dehumidify when needed: In persistently damp periods, a compact dehumidifier or temporary desiccants helps.
- Stay on top of seals: Reseal grout/silicone periodically; fix drips and leaks promptly.
Water ingress is when water makes its way into a building. It can occur for various reasons and in different ways, including through condensation. This can lead to immediate damage or slow deterioration of building elements. If left untreated, it may lead to severe structural damage and expensive repairs, or health issues from mould growth. – VBA
How Advanced Cabinetry Designs for Mould Resistance
- NCC-aligned ventilation: Correct fan sizing, outdoor discharge and make-up air designed in from the start.
- Wet-area detailing: Robust waterproofing, set-downs, falls to wastes and careful junction detailing.
- Climate-aware design: Solutions tuned for Ballarat’s cool temperate conditions.
See our Bathroom Renovations service or visit the Ballarat showroom to discuss your project.
Get Started
Let’s design a bathroom that looks incredible and stays fresh. Request a quote or drop into our Ballarat showroom at 134 Fussell St, Ballarat East.
