Design Workshop: Garage to granny flat

Alicia Brown and Marc Horler are planning to retrofit the red brick garage in their backyard as a temporary living space for their family during house renovations, with an eye to creating a useful ‘granny flat’ for the future too. Building designer Elizabeth Wheeler of Future Focused advises them on a workable layout and what they can achieve with their budget while complying with local regulations.

As part of the planning for a major renovation of their family home in a bayside suburb of Melbourne, Alicia and Marc are considering what they and their two children, aged five and eight, will need to live comfortably during that process.

The garage at the bottom of their garden – currently used as a storage shed – could be retrofitted into a small home to accommodate them during the renovations, but the couple need advice about how best to bring light into the space, put in a new floor, and increase its thermal efficiency. They will also need to contend with getting services to the building.

“We love the shed at the back of our block. It’s a beautiful piece of history and I get so much enjoyment from that,” Alicia says. They hope that the building’s northerly aspect will allow them to maximise solar gain.
Marc and Alicia want to create two bedrooms as well as a kitchen, bathroom, dining area, living area and as much storage as possible. They plan to use as many recycled materials as they can, including spare gas appliances.

Transforming the structure into a liveable space will require some work. “It is quite a dusty space and hard to keep clean at present,” Alicia says. “The wind blows grass clippings and leaves into the shed from the yard.”

Given their budget, Alicia and Marc will need to be clever about doing the work necessary to make this secondary dwelling into a home that can last. They hope that after the family has moved back into the main house, the garage can serve as a place for grandparents, visitors and adult children to stay for years to come.

Elizabeth Wheeler offers advice on a possible layout, how to improve the structure’s thermal envelope, choosing the right windows and doors and how to future-proof the dwelling for a potential older guest with higher mobility needs.

Currently used for storage, the garage features exposed roof trusses and a great northern orientation.

Elizabeth’s response

Your garage is almost perfectly sited for a small secondary dwelling and will provide a great shell to build within. The big caveat here is “if you can get the necessary permits”. Because this is a change of use for the structure (from Class 10a Garage to Class 1 Dwelling), you will need a building permit. And unfortunately, Victoria has some of the most restrictive dual occupancy rules in the country: what we call a ‘granny flat’ can only be used by a dependent family member. A second dwelling for any other purpose triggers a planning permit process and the design needs to comply with the requirements of Clause 55 of the planning scheme, such as carparking and private open space.

I suggest you discuss the specifics of your plans with your local council and with the building surveyor who will be working on your home renovation. They are best placed to advise you on processes and permit costs. Given your budget and purpose, the suggestions below are premised on leaving the structure alone and complying with all aspects of the National Construction Code for a Class 1 building.


You have four options for your floor: leave it as is; re-lay the bricks; build a timber floor over the bricks; or pour an infill concrete slab. Given it’s uneven, dusty and cold, it won’t be comfortable or safe as is. Relaid bricks will still be cold and dusty and are likely to move while they resettle. There’s not enough solar gain to justify adding more thermal mass via a concrete floor. I recommend placing a damp-proof membrane over the bricks and sitting bearers directly on the membrane. Top the bearers with low-VOC particle board and then finish as you desire. A concrete threshold in both doorways will prevent ingress of water and dust; insulation batts between the bearers will give you much more thermal comfort.

Bear in mind that you live in a termite zone. There are damp-proofing membranes that double as physical termite barriers, but whether these will suffice depends on the construction method your builder chooses. Talk through your options with several termite companies to decide what will suit your context.


Even assuming your roof is fully weatherproof, it will still need insulation for the space to be liveable. For Melbourne, modelling has shown R4.5 to be the insulation sweet spot. The cheapest approach would be simply to batten and plaster the bottom chord of the trusses and pop insulation on top. That would also mean less volume to heat, but it doesn’t work spatially and aesthetically. It would also be too low to satisfy the Code.

The next most affordable approach would be to remove the roofing sheets, place an insulated roof blanket on the battens and then put the sheets back on. You can then insulate between the trusses, using strapping or battens to hold batts in place. It’s up to you whether you want to spend the money on having your builder plaster between the rafters rather than over them.

Down the track, if you have some cash to spare, consider filling the cavity inside your brick walls with insulating foam.

Windows and doors

Replacing the windows with new glazing units makes sense thermally and aesthetically. Your budget won’t stretch to reconfiguring the openings, but you’ll be surprised by how much light you gain by clear glazing. Painting your ceiling and most of your internal walls white will also boost the light considerably.

It’s very hard to find timber windows certified by the Forest Stewardship Council. Most are certified by less rigorous schemes that are not supported by environmentalists. Maintenance of timber windows is also a challenge. I recommend either thermally broken aluminium or uPVC double-glazed windows. Aluminium conducts heat, so I counsel strongly against regular aluminium frames. While they are cheaper, you will feel and pay for the unregulated heat transfer in both summer and winter.

From both financial and thermal perspectives, casement windows and hinged doors are going to work better than sashless and bifolds. In uPVC, you also have the option of tilt-and-turn style windows. Whatever you choose, pay careful attention to draught proofing around the windows, especially given that the openings are brick and inherently uneven. The door in the bedroom needs to be glazed to satisfy light requirements.

Shading and privacy

Without eaves, those northern and eastern windows will be hammered in summer. Given you also want some privacy, I’d use a pergola with a deciduous vine on the north. As well as providing shade, this will give a sense of containment and definition to the BBQ area. Awnings would suit the window and new glazed door on the east.

The lack of south-facing openings is a problem, as these provide the best way to cool a Melbourne house in summer. Skylights generally compromise thermal performance, but in this instance a small, openable, high-performance skylight low on the south roof over the bathroom is probably warranted. Hopefully your neighbour’s tree will provide it with some shade as well.

Accessibility and futureproofing

It’s great that you want to futureproof the dwelling. I find the Australian Liveable Housing Guidelines invaluable. They set out a range of provisions for accessibility in a domestic context, such as reinforced walls and circulation space. Ideally, all dwellings would be built at Platinum level accessibility; in reality, especially when converting existing spaces, compromises are necessary.

People are often interested in studio flats for an elderly parent, so for the sake of this exercise, I’ve opted for a floor plan that hovers between Gold and Platinum Level accessibility. Many aspects of the design (bathroom, bedroom, doorways) would accommodate ageing in place and/or someone with higher mobility needs. This might not reflect your priorities, but I hope it gives you and other readers some insights into what might be needed space-wise to achieve some measure of accessibility.

Elizabeth suggests a layout for the garage retrofit that has two sleeping spaces to serve the family in the short term, and that could also work as a granny flat in the future. She also proposes a loft over the eastern half of the building and the bathroom for extra play space for the kids.

Floor plan

With only 48 square metres of floor area and needing to work around existing wall openings, you’re going to need to make some sacrifices. For a family of four, prioritise functionality, storage and room to move. These are what will help you get through six months or more in what some consider to be a small space. I offer one suggested layout at left.

There’s not enough room in the roof for a full mezzanine, but I suggest putting a floor over the trusses on the eastern half of the building and the bathroom. This will contain smells and noise and give your kids some space for their Lego. If you don’t mind crawling in, you can also use the space along the sides for storage. I’d leave the living area end open with a clear glass balustrade. An openable roof window on the south would give this space more amenity and – if placed over the bunk bed – provide much-needed light to that space. Note that neither a mezzanine nor the nook for the bunk would qualify as bedrooms under the Code.

Secondly, although it would be ideal to separate sanitary functions, doing this while maintaining accessibility takes too much room. I have combined bathroom and laundry; removing the tall cabinets opposite the shower would give the bathroom Platinum level accessibility.

Thirdly, I’ve crunched your floor plan a dozen different ways and, without tinkering with structure, I can’t find a viable way to give you two bedrooms that satisfy the light and ventilation aspects of the Code. When you’ve moved back to the main house, you can remove the partition between the two sleeping areas for Platinum accessibility.

If you have different accessibility priorities, then there are other ways to design the space. If you want to redesign, I suggest you make a 1:20 plan and cut out appropriately-scaled shapes of basic furniture. Try to allow at least 90 centimetres of walk space between furniture and allow 110 millimetres for walls. If you place your shower and/or toilet on an external wall, you will need an additional stud wall for plumbing and waterproofing.

Elizabeth Wheeler
Elizabeth Wheeler designs and advises on residential dwellings, materials and products that don’t cost the earth. She has a particular interest in small-scale renovation projects that transform both thermal performance and occupants’ quality of life. Elizabeth’s work is informed by her qualification in Building Design, Bachelor of Arts and three decades of environmental and progressive social justice activism. Her company is Future Focused Buildings.

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