Turn your garage into an office or living space

Add living space to your place by transforming an underutilised garage into an office, granny flat or extra living space.

Bunnings magazine, December 2019

Do you feel like your house is not quite big enough, but an extension seems too pricey? You might be able to convert your garage into an office, or even a granny flat that you can let out.

“Typically, a garage conversion costs around half of what a new build under the main roof would,” says architect Grant Lucas.

Class act

In the National Construction Code (NCC), a garage is categorised as a Class 10a structure, meaning development approval is needed to convert it into a living space meeting the requirements for a Class 1a habitable area. If the garage is integrated into the shell of your home and has a concrete ceiling less than 2.4 metres above the finished floor level – the minimum height for a habitable area – it will probably be unsuitable for conversion.

With a freestanding or externally attached garage, it might be possible to raise the roof to achieve the minimum height requirement. This involves removing the existing roofing and framework, raising the height of the walls, then rebuilding the roof.

Since not all garages can be converted, enlist the help of an experienced architect or building designer. They will be familiar with the NCC and will also be able to advise you on requirements specific to your local area. For example, many local councils stipulate that a freestanding home must include provision for covered parking, so you might only be able to convert part of your garage, unless you plan to add a carport.

Ground control

The waterproofing requirements of a Class 1a habitable structure are stricter than those for an ordinary garage slab. The simplest solution may be to apply a suitable epoxy finish, but in some cases, it will be necessary to add membrane and pour a new slab over the top.

The slab will also need to be inspected for termite resistance, and in most cases, a termite barrier will need to be added, according to your state’s requirements. Once certification standards are met, you can install your choice of flooring.

“If you lay tiles, the concrete must be completely level,” says Mark Deacon, director of Superdraft. A floating floor is another option. “The best materials for floating garage floors are engineered and laminate floors,” adds Mark.

“Alternatively, carpeting will warm up the space and will make the converted garage feel more homely. You will need to use tack strips and lay padding before you install the carpet.”

Hit the walls

If a wall is closer than 900mm to any property boundary, or a secondary dwelling is located within 1800mm of the principal dwelling, the wall would need to be fire-rated. This may mean, among other things, that you cannot have a window or door within that wall.

The walls must be waterproofed by applying membrane or attaching wall wrap. Plus, “the walls and ceiling will need to be insulated and lined with plasterboard,” says Grant.

In NSW, if you are transforming the garage into a granny flat, it will need Building Sustainability Index (BASIX) certification for energy efficiency. In other states and territories, the Nationwide House Energy Rating Scheme (NatHERS) certificate applies to residential dwellings.

For heating and cooling, consider a reverse-cycle air conditioner. Utilising cross-ventilation can reduce your cooling costs, so interior walls should be designed to promote the flow of air when windows are open.

Let there be light!

A habitable structure must have windows with an area at least 10 per cent of the floor area. “The layout of an under-main-roof conversion is usually predefined by the original roller door opening,” explains Grant. The cheapest and easiest conversion may involve removing the garage door and replacing it with a window suite, but this could have engineering implications for the original foundation.

“The likelihood is that the existing footing will amply take the loadings but you will need to have the original house’s engineering drawings to reveal this information,” he explains.

Power and a shower

Many garages only have a 15-amp light circuit, so a licensed electrician will have to upgrade the power supply.

“If you’re looking at installing air conditioning and electric cooking facilities, you would have to run a larger cable, with a new sub-board installed,” says electrician Dean Marsh. And if there will be a tenant living in the new dwelling, you’ll have to hire a suitably qualified electrician to install metering.

Plumbing is a big-ticket item, and one you can leave out if you’re just planning a living area or home office. But if you want a bathroom, the shower area will need to be suitably waterproofed by a licensed plumber, and drainage provided.

One plumbing solution is to have housings for waste pipes cut into the concrete slab. In all, it’s quite a checklist to consider – but once the work is done and the dust has settled, you’ll have a new and comfortable extra space to call home.

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Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions that came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings Team Member.

Grave health hazards are linked to asbestos, which may be in homes built up to 1990. Health hazards may result from exposure to lead-based paints in older materials and copper chromium arsenic (CCA) treated timber. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page. You can also use a simple test kit from Bunnings to indicate the presence of lead-based paint.
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