A garage looks like a ready-made room, but the building code classifies it differently from the house. Turning it into a bedroom, office or rumpus room changes how it is classified, and that change brings a list of approval and construction requirements with it.
Why a garage isn't a room yet
The National Construction Code (NCC) puts a garage in Class 10a, a non-habitable building. A house is Class 1. Guidance from the ABCB says a habitable building, such as a sleepout, can't be classed as Class 10. Once people sleep, work or relax in the space, it must comply with the requirements for the home itself.
That change of use needs approval. Some projects may suit a complying development certificate (CDC), but only where the finished house still satisfies all of that code's standards. Many conversions need a council development application (DA) instead, especially where council controls require the lost parking to be replaced elsewhere on the site. If the plan is a self-contained home with its own kitchen, the work is assessed as a secondary dwelling, and different rules apply. See our granny flats page for that path.
The building code items that usually need work
Garages are built to a lower standard than living areas, so a conversion usually involves more than new carpet. The common items are:
- Ceiling height. The ABCB Housing Provisions allow a garage ceiling as low as 2.1 m, but most habitable rooms need at least 2.4 m. A low garage ceiling can rule out a conversion on its own.
- Natural light. A habitable room needs windows with a light transmitting area of at least 10% of the floor area.
- Ventilation. Openable windows or doors must give a ventilation area of at least 5% of the floor area, unless mechanical ventilation is used where permitted.
- Damp and weatherproofing. Garage slabs often sit close to ground level, may slope towards the door, and may not have been laid over a vapour barrier. The floor may need raising or a new floor system to keep moisture out.
- Termite management. The house's termite system may not extend to the garage, especially if it was built separately.
- Insulation and energy. Walls and ceilings are often uninsulated. A BASIX certificate may be needed depending on the scope and value of the work.
- Smoke alarms. The converted room has to be covered by the home's smoke alarm system.
Fire separation can change too
A garage within 900 mm of a side boundary may have been fine as a Class 10a building, but once it becomes part of the house, its walls are held to the Class 1 fire separation rules. That can mean upgrading the boundary wall to a fire-resisting construction and dealing with any windows in it. Our guide on Garages close to the boundary: fire separation and setbacks explains the 900 mm trigger.
Filling in the garage door
Removing the roller door leaves a wide opening to infill with framing, cladding and usually a window. The existing lintel or beam over the door was designed for a door, not a wall, so a structural check is sensible. The new wall must also be weatherproofed properly where it meets the slab, since this is a common source of leaks. If a bathroom is added, the wet area waterproofing must be inspected before tiling covers it.
What if it was converted without approval?
Many homes are bought with a garage that was converted years ago without approval. That can cause problems at sale time, with insurance, or if council issues an order. A building information certificate is the usual way to regularise this kind of work. Council assesses the work, and upgrades may be required before one is issued.
Planning your conversion
Before committing, measure the ceiling height, check how far the garage is from each boundary, and find out how the slab was built. Those three items decide most conversions. Then ask your designer which approval route suits the project.
CertifiBuild certifies Class 1 and Class 10 work across NSW, including alterations and additions like this. For more on garages generally, see our garages and carports page. If you already have drawings, request a quote and we can outline what certification will involve.
Local help across NSW
CertifiBuild certifies Class 1 and Class 10 work in 39 council areas. Local rules on these council pages are a good place to start: Liverpool City Council, Hornsby Shire Council, North Sydney Council, Burwood Council, Woollahra Municipal Council, City of Parramatta.
Suburb pages with local planning notes: Casula, Cherrybrook, Crows Nest, Croydon Park, Double Bay, Eastwood, Epping, Exeter, Georges Hall, Gladesville. You can also browse every service area.
Sources
- Part A6 building classification, NCC 2022 Volume Two (ABCB)
- Housing Provisions Part 10.3, room heights (ABCB)
- Housing Provisions Part 9.2, fire separation of external walls (ABCB)