Natural light and ventilation in a new SA house

Performance Requirements and the Deemed-to-Satisfy route

NCC 2022 Volume Two states the light requirement as a Performance Requirement. H4P4(1) requires a habitable room to be provided with windows, “where appropriate to the function or use of that part of the building, so that natural light, when available, provides an average daylight factor of not less than 2%.” Verification method H4V2 gives a formula for calculating that factor. H4D6 states that “compliance with Part 10.5 of the ABCB Housing Provisions satisfies Performance Requirement H4P4 for lighting.”

For ventilation, H4P5(1) requires a space used by occupants to be “provided with means of ventilation with outdoor air which will maintain adequate air quality”, and H4P5(3) requires contaminated air to be “disposed of in a manner which does not unduly create a nuisance or hazard to people in the building or other property.” H4D7(2) states that compliance with Part 10.6 satisfies H4P5. H4D7(1) adds that, “except for an exhaust fan from a sanitary compartment, laundry, kitchen or bathroom”, H4P5 is satisfied for a mechanical ventilation system installed in accordance with AS 1668.2, and clause 10.6.1(2) states that Part 10.6 “need not be complied with if H4D7(1) is complied with.”

The window and opening percentages below are therefore Deemed-to-Satisfy provisions. A Performance Solution is another route to the same Performance Requirements. South Australia does not vary Part 10.5 or Part 10.6: the index to its schedule lists variations to Parts 4.2, 9.2, 10.2 and 13.1 of the Housing Provisions and to the referenced documents.

NCC natural light requirements for habitable rooms

Clause 10.5.1(1) states: “Natural light must be provided to all habitable rooms”. Schedule 1 defines a habitable room to include a bedroom, living room, kitchen, dining room, study, family room and similar rooms, and to exclude a bathroom, laundry, water closet, pantry, walk-in wardrobe, corridor and hallway, among others.

Clause 10.5.1(2) sets three ways to provide it, each measured as an aggregate light transmitting area “exclusive of framing members, glazing bars or other obstructions”: (a) windows, excluding roof lights, of “not less than 10% of the floor area of the room” that “are open to the sky or face a court or other space open to the sky or an open verandah, carport or the like”; (b) roof lights of “not less than 3% of the floor area of the room” that “are open to the sky”; or (c) “a proportional combination of windows and roof lights required by (a) and (b).”

The explanatory information works an example for a room of 100 m²: windows of at least 10 m², or roof lights of at least 3 m². It explains the smaller figure for roof lights: a roof light “generally receives greater exposure to sunlight than a window because of its orientation to the sky”.

Windows facing a side boundary, and borrowed light

Clause 10.5.1(3) states: “A window required to provide natural light that faces a boundary of an adjoining allotment must not be less than a horizontal distance of 900 mm from that boundary.”

Clause 10.5.1(4) allows natural light to a room to come through glazed panels or openings from an adjoining room, including an enclosed verandah, where the panels or openings have a light transmitting area of not less than 10% of the floor area of the room lit, and the adjoining room has windows of not less than 10% (or roof lights of not less than 3%, or a proportional combination) of the combined floor area of both rooms. Clause 10.5.1(5) allows those areas to be reduced “as appropriate if direct natural light is provided from another source.” The explanatory information adds that where a doorway is used as the opening, it must provide the light “when in the closed position”.

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Artificial lighting in bathrooms, toilets and laundries

Clause 10.5.2 covers sanitary compartments, bathrooms, shower rooms, airlocks and laundries, which “must be provided with artificial lighting if natural light in accordance with the relevant provisions of 10.5.1 is not available”, either at a rate of not less than one light fitting per 16 m² of floor area or in accordance with AS/NZS 1680.0.

The matching Performance Requirement, H4P4(2), requires artificial lighting “to provide an illuminance of not less than 20 lux appropriate to the function or use of the building to enable safe movement by occupants”, and applies to those rooms “if natural light of a suitable standard is not available.”

Ventilation openings: the 5% rule and borrowed ventilation

Clause 10.6.2 requires ventilation to “a habitable room, sanitary compartment, bathroom, shower room, laundry and any other room occupied by a person for any purpose”. Under 10.6.2(a), it can be provided by “openings, windows, doors or other devices which can be opened— with a ventilating area not less than 5% of the floor area of the room required to be ventilated”, open to a suitably sized court or space open to the sky, an open verandah, carport or the like, or an adjoining room under (b).

The explanatory information states how a window is counted: “The ventilating area of a window is measured as the size of the openable sash of the window”, regardless of whether it is an awning, casement or sliding window and “irrespective of the restrictions on the openable sash.”

Under 10.6.2(b), natural ventilation can come through a window, opening, door or other device from an adjoining room, including an enclosed verandah, if “the room to be ventilated or the adjoining room is not a sanitary compartment”, the opening between them has a ventilating area of not less than 5% of the floor area of the room to be ventilated, and the adjoining room has openings of not less than 5% of the combined floor areas of both rooms. Those areas “may be reduced as appropriate if direct natural ventilation is provided from another source.”

Bathroom and toilet exhaust fan regulations in the NCC

Clause 10.6.2(c) is the third means: “An exhaust fan or other means of mechanical ventilation may be used to ventilate a sanitary compartment, laundry, kitchen or bathroom”, provided “contaminated air exhausts comply with 10.8.2.” Schedule 1 defines a sanitary compartment as “a room or space containing a closet pan or urinal”.

Clause 10.6.3 deals with where a toilet sits: “A sanitary compartment must not open directly into a kitchen or pantry unless— access is by an airlock, hallway or other room”, or “the sanitary compartment is provided with an exhaust fan or other means of mechanical exhaust ventilation.”

Clause 10.8.2, in the condensation management part of the Housing Provisions, sets minimum flow rates for exhaust systems in kitchens, bathrooms, sanitary compartments and laundries, requires the exhaust to discharge to outdoor air, and adds an interlock and run-on timer for some bathrooms and sanitary compartments. Those requirements are set out in a separate note.

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Where these decisions are made for a new house

The percentages in 10.5.1 and 10.6.2 are set against the floor area of each room, so window sizes, roof lights, openable sashes and exhaust fans are settled room by room in the design. Whether a design meets the Deemed-to-Satisfy provisions, or relies on a Performance Solution, is assessed by the relevant authority assessing the building work.

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