A window includes roof lights, glassed louvres and glazed doors (see definition in Schedule 1).

F6D3(1)(a) sets out the requirement for natural light provided by windows other than roof lights. F6D3(1)(b) sets out the requirement for natural light provided by roof lights.

A roof light generally receives greater exposure to sunlight than a window because of its orientation to the sky and consequently, the size of a roof light as a percentage of the floor area served is permitted to be smaller than for a window serving the same floor area.

To achieve the requirements for natural light when both windows and roof lights are provided, a proportional combination of F6D3(1)(a) and (b) can be used through F6D3(1)(c). This is explained in Figure F6D3a below.

Figure F6D3a: Method for determining proportional combination of windows and roof lights

Description of Figure F6D3a

Area of the room which requires natural light is 100 m2. No natural light borrowed from adjoining rooms.

General requirements

Required windows to provide natural light must have a light transmitting area of at least 10% of the floor area. 10% of 100 m² = 10 m²

Or, roof lights to provide natural light must have a light transmitting area of at least 3% of the floor area. 3% of 100 m² = 3 m²

In the formula below, 3% of the floor area is expressed as the fraction 0.03 and 10% of the floor area is expressed as the fraction 0.1.

Formula—for the area of window(s) required to compensate for roof light shortfall

Area of room covered by the roof light = (Area of roof light)/ 0.03

Required window(s) area = [(Floor area) – (Area covered by the roof light)] / 10

Area of windows required to compensate for roof light shortfall

If the roof light = 1 m2

Area of room covered by the roof light = (1 m2 / 0.03) = 33.33 m2 Required window(s) area = (100 m2 – 33.33 m2) / 10 = 6.67 m2

Formula—for the area of roof lights required to compensate for window(s) shortfall

Area of room covered by the window(s)= (Area of window(s)) / 0.1

Required roof light area = [(Floor area) – (Area covered by the window)]/ 33.33

Area of roof lights required to compensate for window shortfall

If the window= 5 m2

Area of room covered by the window(s)= (5 m2 / 0.1 m2) = 50 m2 Required roof lights area = (100 m2 – 50 m2) / 33.33 m2 = 1.5 m2

Notes

For the purposes of Figure F6D3a, a window excludes a roof light.

The same proportional calculation principle applies if—

• two or more windows are used; or
• two or more roof lights are used.

All windows, both required and non-required, must comply with the various requirements of the BCA’s fire-safety provisions, such as C4D3 openings in external walls, and S5C16 for roof lights.

F6D3(2) does not prohibit windows closer to the boundary than one metre (or three metres in the case of a patient-care area in a Class 9a building). However, if a window is located within these distances, F6D3(2) does not allow it to be considered as providing required natural light to the subject room.

It should be noted that F6D3(2) does not apply to Class 9c buildings. F6D3(3) contains specific provisions for these buildings.

Figure F6D3b illustrates the method of measuring the distance of the window from:

• an adjoining allotment boundary;
• a wall of the same building; and
• a wall of another building on the same allotment.

Figure F6D3b: Elevation showing method of measuring distance of window from boundary

F6D3(3) contains requirements for Class 9c buildings. The requirement for the windowsill to be not more than 1 m above floor level and at least 3 m from an adjoining allotment, another building or wall is to maintain amenity for residents who spend a significant amount of time sitting on chairs or lying in bed.  Figure F6D3c illustrates the method of measuring these distances.

Figure F6D3c: Illustration of window sill in an aged care building

F6D3(4) contains requirements for Class 9b early childhood centres. The well-being of children in these types of buildings is enhanced through improved interaction with the outdoor environment by the provision of 50% of window sills in children’s rooms required to be located not more than 500 mm above the floor level.

The following is not considered a children’s room:

• a passageway or thoroughfare (including door swings);
• a toilet and hygiene facilities;
• a room permanently set aside for storage;
• a room for staff or administration;
• a kitchen, unless the use of the kitchen is part of an educational program provided by the service; or
• any other space that is not suitable for children.