Converting a space into a bedroom?

Want to convert your garage, attic or under stairs (Harry Potter bedroom) into another living space or build in under your house? Is it that simple? Well, there are a few things you need to know before jumping into that renovation.

First, let's start with what a habitable room is;

According to the NCC 2019 Volume 2, a habitable room is defined as, "a room used for normal domestic activities, and—

1. includes a bedroom, living room, lounge room, music room, television room, kitchen, dining room, sewing room, study, playroom, family room, home theatre and sunroom; but

2. excludes a bathroom, laundry, water closet, pantry, walk-in wardrobe, corridor, hallway, lobby, photographic darkroom, clothes-drying room, and other spaces of a specialised nature occupied neither frequently nor for extended periods.”

There are a few requirements that habitable rooms require including minimum ceiling heights, natural light, air movement and damp proofing which are explained below:

Ceiling Heights

The first requirement is the ceiling height. The minimum ceiling height for a habitable room is 2.4m. Why? Fire! There's been a lot of research into how fire behaves and how people behave when there is a fire. Put very simply, it can take up to 30mins for a person to escape from a fire and it also takes 30 mins for the smoke to accumulate 30cm deep into the ceiling. So, assuming a person is 2.1m tall then they would have the maximum time of 30 minutes to get out of the house.

A concession allows for 1/3 of the floor area of the room to be below 2.4m but must be above 2.1m and kitchens are an exception as, although technically a habitable room, the height can be 2.1m.

The Measurements of heights of rooms and other spaces was provided by the Australian Building Codes Board © 2019 under the CC-BY-NC-ND licence.

A = 2.4m in a habitable room (excluding a kitchen). B = 2.4m in a habitable room with a sloping ceiling for at least 2/3 of the floor area. C = 2.1m in a non-habitable room with a sloping ceiling for at least two-thirds of the floor area D = 2.2m In an attic with a sloping ceiling for at least two-thirds of the floor area E = 1.5m for the purpose of calculating the floor area of a room or space, any ceiling height of less than 1.5 m is excluded. F = 2.0m In a stairway, ramp or landing (measured vertically above the nosing line of the tread or the floor surface of a ramp)

Natural Light

All habitable rooms must be provided with natural light. This light must be provided by windows or roof lights. Windows must have an aggregate light transmitting area measured of not less than 10% of the floor area of the room and are open to the sky or other open space such as a verandah or carport. Roof lights must have an aggregate light transmitting area of not less than 3% of the floor area of the room and are open to the sky.

The Method for determining proportional combination of windows and roof lights was provided by the Australian Building Codes Board © 2019 under the CC-BY-NC-ND licence.

However, if you can’t get that natural light, there is a concession were borrowed light can be used. This light much pass through a glazed panel(s) or openings from an adjoining room and the size of the glazed panel between the two rooms is 10% of the room and the window to natural light is 10% of the combined room floor areas.

The Method of determining areas of openings for borrowed light was provided by the Australian Building Codes Board © 2019 under the CC-BY-NC-ND licence.

Air Movement

Air movement must also be provided in habitable rooms. Toowoomba and the Southern Downs Region are within the Climate Zone 5 according to the Australian Building Codes Board. The minimum total ventilation opening area as a percentage of the floor area must be 7.5% (without a ceiling fan), 5% with a ceiling fan and be connected by a breeze path with another ventilation opening in another room or be provided by a minimum of two ventilation openings in the same room having not less than 25% of the area required by the above minimum percentages.

Damp proofing

Damp proofing is where a polyethylene film vapour barrier is placed on the ground before the slab is poured and is required for slab on ground construction of Class 1 dwellings and Class 10 structures attached to Class 1 dwellings. This has only been a requirement for construction recently so usually damp proofing wasn’t necessarily undertaken in older homes in garages and under slabs in highset houses. Floor finishes can have issues with rising damp if there is no vapour barrier under the slab. This can be rectified by:

1. Ripping up the old slab and redoing it with the vapour barrier;

2. placing a vapour barrier on top of the existing slab and pouring another, thinner slab on top; or

3. providing a liquid damp proof membrane over the existing slab placing the finished floor on top.