Exhaust Fan Compliance
Recently, there has been an increase in the numbers of complaints the VBA has received in relation to the non-compliant discharge of exhaust fans.
Specifically, exhaust fans are being installed in bathrooms and sanitary compartments with the contaminated air inappropriately being discharged into unventilated roof spaces. The incorrect discharge of exhaust fans can lead to condensation, mould growth and degradation of structural members, resulting in costly rectification work.
Builders are reminded of the DTS requirements of NCC Vol.2 – 2019 Clauses 3.8.7.3 and 3.8.7.4 (replicated below).
3.8.7.3 Flow rate and discharge of exhaust systems
(a) An exhaust system installed in a kitchen, bathroom, sanitary compartment or laundry must have a minimum flowrate of—
(i) 25 L/s for a bathroom or sanitary compartment; and
(ii) 40 L/s for a kitchen or laundry.
(b) Exhaust from a bathroom, sanitary compartment, or laundry must be discharged—
(i) directly or via a shaft or duct to outdoor air; or
(ii) to a roof space that is ventilated in accordance with 3.8.7.4.
3.8.7.4 Ventilation of roof spaces
(a) Where an exhaust system covered by 3.8.7.3 discharges into a roof space, the roof space must be ventilated to outdoor air through evenly distributed openings.
(b) Openings required by (a) must have a total unobstructed area of 1/300 of the respective ceiling area if the roof pitch is more than 22°, or 1/150 of the respective ceiling area if the roof pitch is not more than 22°.
(c) 30 per cent of the total unobstructed area required by (b) must be located not more than 900 mm below the ridge or highest point of the roof space, measured vertically, with the remaining required area provided by eave vents.
Additionally, building surveyors and building inspectors are reminded that compliance of exhaust fan discharges can usually be verified at a final inspection, with either the discharge point of exhaust fan ducting or shaft being externally visible, or the appropriate roof ventilation being installed. (Source VBA Technical Bulletin June 2022)