The Building Code of Australia has a minimum requirement for natural light to a habitable room. It is calculated based on the floor area of a habitable room. A window opening is required that has an area 10% of the floor area of the room. Light may also be borrowed from the adjoining room. The area of the two rooms is combined, and openings provided must equal 10% of the total floor area for compliance.
A concession is provided in the Building Code of Australia (Part of the National Construction Code – NCC) that allows the use of rooflight installations to provide an equivalent level of natural light using a smaller area.
The concession is based on the exposure provided to a rooflight when compared to a wall window affords a greater level of lighting to the space. So when using a roof light in a room or in addition to windows provided, the ratio of opening to floor area is reduced from 10% to 3% or a combination of the two when both are provided.
For example: For a 20m2 room the minimum area required for natural light is 10%. If a rooflight is installed only 0.6m2 would be required.
If the roof light was only 0.3m2, then a window or equivalent borrowed light would be necessary. This would need to be an additional 1.0m2.
Note: Energy efficiency provisions also take into account this concession (in Climate zone 6 only). Air flow through a building is improved when high and low openings are provided. So by using an openable roof light would facilitate air movement through the home.