Light and ventilation calculator
Enter the room's floor area and the glazing and openings it has, direct or borrowed through an adjoining room or a roof light. The gauges show what the room needs against what it has, with the clause.
What it checks
The same engine as the calculator in AEC Assistant, with every table checked against NCC 2025 or the Standard it calls up. The same inputs always give the same result.
You enter
- House or apartment, and the kind of room
- Floor area of the room
- Glazed and openable areas to the outside, with any roof lights
- Or, for borrowed light and air, the adjoining room's floor area, the opening between the rooms and its own glazed and openable areas
It reads from
- NCC 2025 Housing Provisions 10.5.1 and 10.6.2
- NCC 2025 Volume One F6D2 to F6D8
A worked example
The calculator's example inputs, checked.
Floor area glazed
12.0%
of floor area glazed — needs ≥ 10% · habitable room
Complies with NCC 2025 Housing Provisions 10.5.1(2) on the figures entered. The requirements marked for checking still apply on site.
- Glazing needed10% of the floor area = 0.10 × 20 m² = 2.00 m²NCC 2025 Housing Provisions 10.5.1(2)
- Openable area needed5% of the floor area = 0.05 × 20 m² = 1.00 m²NCC 2025 Housing Provisions 10.6.2(a)
- Natural light — glazed area2.40 m² (12.0%) · limit ≥ 2.00 m² (10%)NCC 2025 Housing Provisions 10.5.1(2)
- Ventilation — openable area1.20 m² (6.0%) · limit ≥ 1.00 m² (5%)NCC 2025 Housing Provisions 10.6.2(a)
Questions
How much window does a habitable room need?
Natural light through windows of at least 10% of the floor area, or roof lights of at least 3%, and ventilation openings of at least 5% of the floor area, under Housing Provisions 10.5.1 and 10.6.2 and Volume One Part F6. A habitable room in a house can instead be ventilated mechanically to AS 1668.2 (Volume Two H4D7(1)) or naturally to AS 1668.4 (H4D7(2)(b)), so where the openings fall short the calculator names those routes and marks the room for checking rather than failing it.
Does borrowed light count?
Yes, within limits. Borrowed light needs an opening of at least 10% of the room's area and windows of 10% of the combined floor area (10.5.1(4)); borrowed ventilation uses 5% and 5% (10.6.2(b)). The calculator handles both.
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Ask about the rooms on your own project
The free plan answers from the National Construction Code, state building and planning legislation, ABCB handbooks, regulator practice notes and codes of practice, with the clause cited. No credit card.