Understanding Natural Light Requirements

Natural light is required in certain buildings and rooms. The purpose is to provide daylight, improve comfort, and support health and well-being.

This article explains where natural light is required, how to calculate it, the rules for windows and roof lights, and when light may be borrowed from another room.

Where is Natural Light Required?

Not every room needs a window, but specific "habitable" or "sleeping" spaces do. The requirements apply to:

• Class 1, 2 & 4 (Apartments and houses attached to businesses): All habitable rooms.

• Class 3 (Hotels, hostels, backpackers): All bedrooms and dormitories.

• Class 9a & 9c (Hospitals and Aged Care): All rooms used for sleeping.

• Class 9b (Schools and Childcare): All general classrooms and early childhood playrooms.

How to Calculate Light Requirements

Light is calculated as a percentage of the room's floor area. The measurement must only include the clear glass area, excluding frames or obstructions.

Requirements for the Light Source

To count as a valid source, windows and roof lights must meet specific placement rules:

1. General Placement

• Windows must be open to the sky or face a court, verandah, or carport.

• Roof lights must be open to the sky.

2. Distances from Boundaries or Walls

Except for Class 9c aged care buildings, a window must have a minimum horizontal distance from a boundary or another wall. This distance is the greatest of:

• 1 metre (standard).

• 3 metres (patient care area or other room used for sleeping purposes in a Class 9a building ).

• 50% of the square root of the exterior height of the wall in which the window is located, measured in metres from its sill.

3. Specialised Requirements

• Aged Care (9c): Windows must be transparent and located on an external wall. The sill must be no higher than 1 metre above the floor. They must be at least 3 metres from boundaries.

• Childcare (9b): To let children see out, 50% of the required windows must have sills no higher than 500 mm above the floor.

Borrowed Light: Light from Other Rooms

In some cases, a room can "borrow" light from an adjoining room.

Conditions for Borrowing Light

• Same Unit or Approved Area: Both rooms must be in the same sole-occupancy unit, or the enclosed verandah must be common property. 

• Internal Opening: Glazed panels or openings between rooms must have an area of at least 10% of the "inner" room's floor area.

The Calculation

If you borrow light, the windows in the "outer" room must be larger to compensate for the extra floor space.

• Windows: Must be 10% of the combined floor area of both rooms.

• Roof Lights: Must be 3% of the combined floor area of both rooms.

Note: If the inner room also has a small window of its own, these "borrowed" requirements can be reduced proportionally.

We teach this and so much more at ARCHI UPSKILL. Head to our documentation & detailing courses to learn more.