Damp Bathrooms That Never Dry
If your Adelaide bathroom stays damp, fogs up for hours or has recurring mould, the ventilation isn't working properly — and it may not be compliant.
Key fact: a ten-minute shower in an average bathroom introduces around 200–400 ml of water vapour into the air. Effective bathroom ventilation needs to remove that moisture load before it settles on walls, ceilings and grout — where mould will grow within days.
Why bathroom moisture is a serious problem
Bathroom moisture doesn’t stay in the bathroom. In a home without adequate extraction, humid air migrates through the building — settling in adjacent bedrooms, condensing behind walls, penetrating insulation and accumulating in roof spaces. What starts as a damp bathroom becomes a mould problem in a wardrobe, then timber decay in a wall frame.
In modern airtight homes, this migration is especially problematic because there are fewer incidental pathways for the moisture to disperse. Without deliberate, designed extraction, bathroom humidity has nowhere to go.
Why most bathroom exhaust fans underperform
Most homes have exhaust fans. Most bathrooms still have moisture problems. The gap is almost always in installation quality, system design or compliance — not the fan itself.
Ducted into the roof cavity, not outside
The single most common installation failure. A fan that vents into the roof pumps warm, humid air into the roof space where it condenses and causes damage. NCC 2022 Part 10.8.2 requires exhaust to discharge directly outside via a duct or shaft. Roof cavity venting is explicitly non-compliant.
Duct runs that are too long or kinked
Exhaust duct runs over approximately 3–4 metres, or with multiple bends, dramatically reduce airflow. A fan rated at 50 L/s may deliver less than half that at the end of a long, kinked duct run. The fan sounds like it's working but isn't moving enough air.
Undersized for the room
Fan sizing should be based on room volume and shower usage patterns — not a generic spec. Bathrooms with open showers, large enclosures or high ceilings require proportionally more extraction capacity. Under-specification is very common in volume housing.
Not running long enough after showering
Much of the moisture generation in a shower occurs during and immediately after. A fan that turns off with the light — or is manually turned off — stops extracting before the humidity has cleared. NCC 2022 now requires a minimum 10-minute post-off run period for bathrooms without natural ventilation.
No make-up air in airtight homes
An exhaust fan creates negative pressure in the bathroom. In a well-sealed home, there may not be enough air infiltration to replace what the fan is removing. This reduces the fan's effective airflow — sometimes significantly. In very airtight homes, bathroom exhaust must be balanced against a fresh air supply to the home.
NCC 2022: what the code now requires
The National Construction Code 2022 introduced specific requirements for bathroom exhaust systems that directly address the most common installation failures:
Direct outdoor discharge
Exhaust fans in bathrooms, kitchens, sanitary compartments and laundries must discharge directly to outdoor air via a duct or shaft. Venting into a roof cavity, sub-floor or enclosed space is not compliant.
Light switch interlock with 10-minute delay
For bathrooms and sanitary compartments without natural ventilation (i.e. no window), the exhaust fan must be interlocked with the light switch — turning on when the light turns on, and continuing to operate for a minimum of 10 minutes after the light is turned off.
Mechanical ventilation for homes under 5 ACH50
Homes with airtightness below 5 air changes per hour at 50 Pascals require whole-home mechanical ventilation meeting a minimum calculated airflow rate. Bathroom exhaust is part of — but not a substitute for — this whole-home requirement.
The better solution: MVHR extraction
A standalone exhaust fan, even a well-installed one, only extracts when it’s running — typically for the duration of a shower and a short period after. For the rest of the day, the bathroom is passively ventilated (or not ventilated at all if there’s no window).
A whole-home MVHR system extracts from bathrooms continuously, 24 hours a day. Bathrooms are maintained in slight negative pressure relative to living spaces — meaning moisture generated in the bathroom is drawn out toward the extract terminal and removed, rather than diffusing into adjacent rooms. The bathroom dries faster, stays drier, and mould is prevented at the source rather than managed after the fact.
For new builds and high-performance homes in Adelaide, MVHR is the right specification. For existing homes where a full MVHR installation isn’t practical, a correctly specified, properly ducted standalone extraction system — meeting NCC 2022 requirements — is the minimum acceptable standard.
Signs your bathroom ventilation isn’t working
- ✓Steam lingers for 30+ minutes after a shower
- ✓Mirror takes more than 10–15 minutes to clear
- ✓Mould returns to the same spots despite cleaning
- ✓Grout discolouration that doesn't come clean
- ✓Peeling paint or bubbling on the ceiling
- ✓A persistent damp or musty smell
- ✓Condensation running down tiles after showering
- ✓Mould appearing in the adjacent bedroom or hallway wardrobe
Frequently asked questions
Why does my bathroom stay damp even with an exhaust fan?
Several reasons: the fan may be undersized for the room volume; the duct may be too long, kinked or venting into the roof cavity instead of directly outside; the fan may not run long enough after showering; or the bathroom may lack adequate make-up air, creating negative pressure that reduces extraction efficiency. In airtight homes especially, exhaust fans struggle without a corresponding fresh air supply.
What does NCC 2022 require for bathroom exhaust fans?
Under NCC 2022 Part 10.8.2, bathroom exhaust fans must discharge directly to outside via a duct or shaft — not into a roof cavity. For bathrooms without natural ventilation (a window), the exhaust system must be interlocked with the light switch and continue to run for at least 10 minutes after the light is turned off. These requirements apply to all new homes and to renovation work on existing homes.
Is it OK to duct a bathroom exhaust fan into the roof cavity?
No. This is non-compliant under NCC 2022 Part 10.8.2 and is one of the most common installation errors in Australian homes. Venting warm, humid bathroom air into a roof cavity causes condensation on the underside of the roof and in insulation, leading to mould growth, timber decay and insulation damage — often not discovered until significant damage has occurred.
How do I stop mould growing in my bathroom in Adelaide?
First, ensure your exhaust fan is correctly ducted directly outside, is appropriately sized for the room, and runs for long enough after showering. Second, consider whether your home has adequate make-up air — in airtight homes, a whole-home MVHR system that continuously extracts from bathrooms is far more effective than a standalone exhaust fan. MVHR keeps bathroom air permanently in negative pressure relative to the rest of the house, preventing moisture migration into living areas.
Persistent damp bathroom in Adelaide?
Whether you need a properly specified standalone exhaust system or a whole-home MVHR solution, HiPer Haus can help. Talk to us about your situation.