Tasmania Rental Ventilation Requirements: The 5% Rule and Exhaust Fans

Poor ventilation is behind most mould disputes in Tasmanian rentals. Date-stamped records showing how the property met the ventilation standard at the start of the tenancy can help in a dispute. Section 36O of the Residential Tenancy Act 1997 sets specific ventilation requirements for every habitable room, bathroom, toilet and laundry.

The 5% Floor Area Ratio

Habitable rooms requiring natural ventilation must have openable windows or wall vents with a combined area equal to approximately five percent of the room's total floor area. That number aligns with National Construction Code principles.

In practice: a 10 square metre bedroom needs about 0.5 square metres of openable window area. A 20 square metre living room needs about one square metre.

Measure the openable portion of the window, not the total glazed area. A large fixed-pane window with a small top-hung opener provides far less ventilation than its size suggests.

The 15cm Locking Rule

Where an openable window is the sole ventilation source for a room, it must be capable of being fixed or locked in an open position with a gap of at least 15 centimetres. The idea is continuous airflow while maintaining security against intruder entry.

Standard window winders and friction stays usually satisfy this. If a window cannot hold a 15 cm gap — because the stay is broken, the winder slips or the lock mechanism prevents partial opening — it fails the standard.

Exhaust Fans in Windowless Wet Areas

Bathrooms, toilets and laundries that do not have an external window must be fitted with a functioning mechanical exhaust fan. The fan must vent directly to outside air or into a roof space that has open eaves or ceiling vents — not into a sealed cavity.

A fan that merely recirculates air within the room (a recirculating rangehood, for instance) does not meet this requirement. Neither does a fan whose ducting terminates inside a sealed roof space with no eave or soffit ventilation.

Why This Standard Matters More in Tasmania

Tasmania's cold, humid climate makes ventilation critical. Without adequate airflow, moisture from showers, cooking and even breathing condenses on cold surfaces — particularly single-glazed windows — and creates ideal conditions for mould growth.

When mould appears mid-tenancy, liability depends on the cause. Structural causes (defective exhaust fans, inadequate window ventilation, rising damp) fall on the landlord under sections 36I and 36O. Tenant-caused moisture (not using installed fans, drying laundry indoors with windows shut) falls on the tenant under section 53.

The distinction matters in bond disputes and RTC repair order applications. If your exhaust fan was non-functional or your ventilation was below the five percent threshold when the tenancy started, you will struggle to argue the mould was the tenant's doing.

Penalties

A ventilation breach carries the standard Part 3B maximum: 50 penalty units ($10,650 at the FY 2026–27 rate of $213 per unit). The Residential Tenancy Commissioner can order repairs, and municipal councils can also intervene under the Public Health Act if the ventilation failure creates an environmental health hazard.

A ventilation audit before each new tenancy takes 15 minutes with a tape measure and catches problems that would otherwise surface as mould complaints six months later. The Rental Minimum Standards in Tasmania guide includes room-by-room ventilation checks alongside every other Part 3B standard, plus a mould-and-dampness inspection protocol.

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