You have spent weeks choosing tiles, fixtures, and finishes. The renovation looks beautiful. Then six months later you notice a dark patch forming at the edge of the ceiling, a persistent musty smell that just will not shift, or grout lines that are starting to discolour no matter how often you clean them.
In most cases, the culprit is the same: ventilation that was inadequate, incorrectly specified, or improperly installed during the renovation.
Bathroom ventilation is one of the most commonly underestimated elements of any renovation – and one of the most expensive to fix after the fact. Here is what goes wrong most often, and how to avoid it.
Mistake One: Installing an Exhaust Fan That Is Too Small for the Room
Exhaust fans are rated by the volume of air they can move, typically expressed in litres per second (L/s) or cubic metres per hour. A fan that is correctly rated for a small ensuite may be completely inadequate for a larger bathroom with a shower, bath, and separate toilet.
The general guide for Australian bathrooms is to achieve at least 25 litres per second of airflow for spaces up to around 10 square metres, with higher capacity required for larger rooms or bathrooms that lack any natural ventilation. Many builders and renovators install a basic fan without calculating whether the capacity is correct for the specific room – and homeowners pay the price.
When specifying your renovation, ask your tradesperson to confirm the fan capacity against the room volume. It is not an expensive upgrade to get right, but it is an expensive problem to fix once tiles are on the walls.
Mistake Two: Venting Into the Roof Cavity Instead of Outdoors
This is a surprisingly common installation error that causes serious damage over time. An exhaust fan that is ducted into the roof cavity rather than outside the building pushes moist air from the bathroom directly into the roof space, where it condenses on structural timber, insulation, and ceiling materials.
The result is mould in the roof cavity, potential structural timber damage, and eventually – often years later – visible mould and staining on ceilings. By the time homeowners notice the problem, the damage can be extensive.
Any exhaust fan must be ducted to an external vent – through the roof, through an eave, or through an external wall. Check this during your renovation before the wall or ceiling is closed up. If you are buying a home and want to check, you can sometimes spot improper ducting during a building inspection.
Mistake Three: Positioning the Fan in the Wrong Location
Where the exhaust fan is placed within the bathroom affects how effectively it removes moisture. A common mistake is installing the fan near the door or in the far end of the bathroom away from the shower – meaning the steam from the shower has to travel across the entire room before reaching the fan, and much of it condenses on walls and ceilings along the way.
Ideally, the exhaust fan should be positioned directly above or as close as possible to the shower. In a bathroom with a separate bath and shower, a second fan or a larger central fan may be more effective than a single unit positioned at one end.
Mistake Four: Forgetting to Account for the Door Seal
An exhaust fan needs a source of replacement air to work effectively. If a bathroom door has a very tight seal at the bottom with no gap for air movement, the fan can create a negative pressure situation where it struggles to move air efficiently.
This is more common in newer construction where air tightness is prioritised. The solution is simple – ensuring there is adequate undercut on the bathroom door so air can flow in from the hallway while the fan exhausts moisture outward.
Mistake Five: Not Running the Fan Long Enough After a Shower
This is a behavioural issue rather than a renovation one, but it is worth mentioning because it affects even well-installed systems. A shower generates a significant volume of moisture, and turning the fan off immediately after leaving the bathroom does not give it time to remove all of that moisture.
The general recommendation is to run the exhaust fan for at least ten to fifteen minutes after a shower. Timer switches – which automatically run the fan for a set period after you leave the room – are a practical solution and cost very little to install. Humidity sensors that run the fan until moisture levels normalise are another option at a modest price premium.
What Proper Ventilation Actually Achieves
Getting ventilation right protects your renovation investment significantly. Tiles, grout, paint, and cabinetry last much longer in a properly ventilated bathroom. Mould and mildew growth – the single most common source of premature bathroom deterioration – is minimised. Air quality is better. And the chance of structural damage to surrounding walls and roof framing is substantially reduced.
It is one of those elements that costs very little to do correctly during a renovation and a great deal to rectify afterwards.
Planning a Bathroom Renovation in Sydney?
Novalé designs and delivers bathroom renovations that are built to last – which means getting the details that matter, including ventilation, right from the start. Our team will ensure your renovation is specified correctly so you are not dealing with avoidable problems down the track.
Get in touch with the Novalé team on 1800 NOVALÉ to start planning your dream renovation with confidence.
