Bathroom Ventilation and Mould: How to Keep a Bathroom Dry

By the Baroco team, Mount Waverley · Updated October 2026

01Why Melbourne bathrooms grow mould

Mould needs three things: moisture, warmth and a surface to feed on. Bathrooms provide all three almost every day. In Melbourne's cool months, warm shower steam condenses on cold tiles, mirrors, ceilings and window glass, and that thin film of water is enough for mould spores to settle and multiply.

Poor ventilation makes it worse. If moist air cannot escape, it soaks into paint, plaster, grout and silicone. Once mould takes hold in porous surfaces, it is harder to remove and can cause ongoing health problems for anyone with allergies or asthma. The fix is to remove moisture at the source before it condenses.

A renovation is the best time to get this right. You can plan ducting, electrical wiring, window placement and surface choices together, rather than retrofitting later.

02Exhaust fans: duct outside, not into the roof

An exhaust fan only works if it removes air from the room and sends it outside. Venting into the roof space is a common shortcut that pushes warm, wet air onto timber and insulation. Over time this can cause roof rot, rusted fixings and hidden mould. The duct must terminate outside through an eave, wall or roof cowl.

Sizing depends on the room volume and how much steam you produce. A fan rated around 90 cubic metres per hour will handle most small bathrooms and ensuites up to about 5 square metres. Larger family bathrooms or double showers need more extraction. If you run a rain shower or steam shower, consider a higher-capacity inline fan.

Duct runs should be as short and straight as possible. Use rigid or semi-rigid ducting rather than long lengths of flexible vinyl, which sags and traps condensation. Insulate any duct in an uninsulated roof space so warm moist air does not cool and turn to water before it exits.

• Position the fan near the shower but away from the door to draw moist air across the room.
• Choose a fan with a draft stopper to reduce cold air coming back in.
• Hardwiring the fan must be done by a licensed electrician.

03Run-on timers and smart controls

Turning the fan off as you leave the bathroom traps humidity inside. A run-on timer keeps the fan running for a set period after the light or switch is turned off. Ten to fifteen minutes is usually enough for a normal shower; longer if you use lots of hot water or the room stays steamy.

A humidistat or moisture-sensing switch can automate this. It starts the fan when humidity rises and stops it when levels drop. This is useful in family bathrooms where people forget to switch the fan on. Electricians can wire these controls during a renovation with minimal extra cost.

If you have a separate toilet or powder room, a smaller fan on a shorter run-on timer is enough. Make sure any timer is compatible with the fan and installed by a licensed electrician.

04Windows and natural ventilation

Opening a window after a shower helps, but Melbourne winters make this less practical. A window alone is rarely enough because cold outside air does not carry moisture away as well as a fan, and you will not want to leave it open long enough. Use windows as a secondary measure when weather permits.

If you are renovating, consider a window that can be locked in a slightly open position or a small awning window above the shower. This lets you air the room without compromising security or privacy. Cross ventilation from a second window or door helps dry the room faster.

Never rely on a window as your only moisture removal. The Building Code and Australian Standards expect mechanical ventilation in bathrooms without an openable window, but a fan is worth installing even with one.

05Heated towel rails and other drying aids

Wet towels left in a bathroom add a surprising amount of moisture to the air. A heated towel rail dries towels between uses so they do not stay damp and odorous. In a renovation, plan the rail near the shower or bath, on its own circuit so it can run on a timer or be switched independently.

Underfloor heating also helps by warming the whole room and speeding evaporation from the floor. It is not a substitute for an exhaust fan, but it makes the bathroom more comfortable and reduces condensation on floor tiles. A programmable thermostat can warm the floor before morning showers.

If you are choosing a heated towel rail, check the wattage and whether it is suitable for the size of your bathroom. Some are plug-in, but a hardwired rail looks neater. Any hardwired installation must be done by a licensed electrician. Baroco Interior Innovations has a showroom at 21/105-111 Ricketts Road, Mount Waverley where you can see heated towel rails and fans with different finishes.

06Silicone, cleaning and routine maintenance

Silicone seals the gaps between tiles, baths, basins and shower screens. It eventually breaks down, especially where it stays wet. Look for shrinking, cracking, black spots or peeling. If mould has grown into the silicone, surface cleaning will not kill the roots, and the only long-term fix is to cut out the old silicone and apply a fresh bead of a quality neutral-cure, mould-resistant sealant.

Daily habits make the biggest difference. Use a squeegee on shower walls and glass after the last shower of the day. Wipe down the basin and bench. Leave the shower screen door open so air can circulate. Wash bath mats and towels regularly, and do not let bottles and soap build up in corners where moisture collects.

For routine cleaning, use a pH-neutral cleaner on tiles and grout, and avoid harsh abrasives that wear the glaze. White vinegar or hydrogen peroxide can remove surface mould from tiles and glass, but test on a hidden area first. Never mix cleaning products, especially anything containing bleach with acids. If you are planning a full renovation, talk to a specialist about ventilation before walls are sheeted. Baroco Interior Innovations can coordinate the electrician and ensure the fan, ducting and controls are ready before tiling begins.

• Squeegee shower walls and glass after each use.
• Replace cracked or black-spotted silicone; surface cleaners won't fix embedded mould.
• Use white vinegar or hydrogen peroxide for surface mould, but test first.