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Granny flat layouts and the rules that shape them

From Modular Living Australia — the independent knowledge base Last updated: 8 Oct 2026

The Livable Housing Design Standard, introduced in NCC 2022 for houses, sets compulsory provisions for dwelling access, the dwelling entrance, internal doors and corridors, the toilet and the shower, based on the silver level of the Livable Housing Design Guidelines.^[1][4][5] It does not apply in New South Wales, and Western Australia's government has stated that it intends to disallow it.^[2][3] One commercial source puts the cost of compliance for a secondary dwelling at A$5,000–A$15,000.^[6]

Most published material on granny flat layouts consists of floor plans. This guide does not offer any, because the useful information is upstream of the plan: the floor area cap, the mandatory accessibility provisions, the open space requirement and the services route between them determine what layouts are possible, and a plan drawn without them is decoration. A 60 square metre secondary dwelling has meaningfully less usable area than 60 square metres implies, and knowing why is what allows a design brief to be written properly.

Livable housing design applies in most states, but not all §

NCC 2022 introduced requirements that mean fewer steps where possible, more space in the bathroom, wider doorways, and provision for future adaptations such as grabrails. They are based on the silver level of the Livable Housing Design Guidelines, first published by Livable Housing Australia^[1].

Where they apply, the provisions cover Class 1a buildings — which is what a detached secondary dwelling generally is. Part H8 requires at least one level and step-free entrance door from the required access path, internal doors and corridors on the ground or entrance level that facilitate unimpeded movement between spaces, and walls of the sanitary compartment, the shower, and a bath other than a freestanding bath constructed so as to facilitate future installation of grabrails in a way that minimises removal of existing wall linings^[7].

A state practice note sets out the compulsory parts as five: dwelling access, dwelling entrance, internal doors and corridors, sanitary compartment, and shower — with at least one shower required to have a hob-less, step-free entry^[5].

The standard is primarily based on the Silver level of the fourth edition guidelines from 2017, and the national baseline took effect on 1 October 2023 for Parts H8 and G7.^[4]

Whether these provisions apply depends on the state or territory. The Australian Building Codes Board's NCC 2022 adoption table, stated to be correct as at 22 September 2023, lists them as commencing on 1 October 2023 in the Northern Territory, 1 May 2024 in Victoria and 1 October 2024 in South Australia and Tasmania, with Queensland and the ACT applying them through their own implementation arrangements.^[8] New South Wales does not apply them: the NSW variation to Part H8 states that livable housing design requirements do not apply to Class 1a buildings in NSW.^[2] Western Australia's government has stated that it intends to disallow the provisions, which requires amendments to the Building Regulations 2012.^[3]

Where the provisions do apply, implementation was phased in some places: Tasmania from 1 October 2024, with internal doors and corridors applying from 1 October 2025, and Queensland from 1 October 2023 under Queensland Development Code 4.5 Modern Homes.^[4]

Concessions exist but are narrower than often assumed. Exemptions apply mainly to the external access path — where site slopes exceed 1:14 or spatial constraints prevent compliance — while the internal provisions remain mandatory where the standard applies^[4].

What that does to a small floor plan §

On a full-sized house these provisions are absorbed. On 60 square metres they are the plan.

Wider internal doors and corridors consume floor area that a compact dwelling does not have spare. A hob-less step-free shower changes the bathroom's floor construction and drainage rather than just its fittings. Clearances around the toilet pan set a minimum sanitary compartment size that a small dwelling cannot design below. Wall reinforcement for future grabrails is cheap to build in and expensive to retrofit, so it is done at framing stage or not at all. And a step-free entrance interacts with the site: on a sloping block, achieving it may require regrading, a ramped path, or lifting the dwelling and adding a compliant approach.

One published estimate puts livable housing compliance for wheelchair accessibility at A$5,000 to A$15,000 on a secondary dwelling project^[6]. That is a cost figure rather than an area figure, and the area cost is the one that constrains the design: every square metre spent on circulation is a square metre unavailable to a bedroom.

The practical consequence is that a compliant 60 m² two-bedroom dwelling is tight, and a compliant 60 m² two-bedroom dwelling with a separate laundry and generous storage generally is not achievable. Something gives, and it is better for the owner to choose what gives than for the drafter to.

The cap is not measured the same way everywhere §

Floor area caps are stated in similar-looking numbers that are not comparable.

Western Australia's 70 square metre limit applies to enclosed internal living area, and does not include verandahs, patios or carports, subject to local site coverage rules^[9]. That permits a design strategy unavailable where the cap covers total area: move amenity outdoors. A covered outdoor living area is among the cheapest square metres in any build, it is not counted, and it substantially improves how a small dwelling lives.

Elsewhere the measurement basis differs, and applying a Western Australian design to another state's cap can put a compliant plan over the line. The cap that applies, and what it measures, is the first thing to establish — see the granny flat rules series for each jurisdiction.

Open space competes with footprint §

South Australia illustrates a constraint that is easy to miss because it is not about the building. The Planning and Design Code requires a minimum of 20 square metres of private open space accessible to the ancillary accommodation, and on a 600 square metre lot already carrying a primary dwelling with its own open space allocation, this reduces the residual rear yard available for the secondary dwelling footprint^[10].

A design that satisfies the floor area cap can still fail on siting for this reason. Where a jurisdiction imposes a private open space requirement, it should be plotted on the survey before the dwelling is placed, not afterwards.

Services can dictate where the building sits §

Tasmania provides the clearest example. A Tasmanian secondary residence cannot have its own separate connections for power, water or sewerage and must share the main dwelling's services, which dictates where the building can be placed and can force a longer and more awkward service run^[11].

Even where independent connections are permitted, the same logic applies with money instead of law: wet areas placed on the far side of the dwelling from the existing sewer connection add trenching, and on a constrained block that trenching may have to route around established trees, paving or the main dwelling's own services.

The efficient move is to locate the bathroom, kitchen and laundry against a single wet wall on the side closest to the existing services. It is also the move that most reduces plumbing cost, which is why compact dwellings that look repetitive across builders' catalogues generally look that way for a reason.

Writing a design brief §

The sequence that avoids redesign is to establish the constraints before the layout:

• The floor area cap that applies, and precisely what it measures.
• Any private open space or site coverage requirement, plotted on a current survey.
• Setbacks required for the fast approval pathway in that jurisdiction.
• Whether independent service connections are permitted, and where the existing connections run.
• Whether the site can achieve a step-free entrance, or whether an access path concession applies.
• Which livable housing provisions apply on the relevant adoption date.
• What must be given up to fit — storage, a separate laundry, or a second bedroom.

What is not covered here §

This guide does not reproduce the dimensional requirements of the Livable Housing Design Standard; the ABCB standard and the relevant state practice note are the authority and should be read with a building surveyor. Solar orientation, thermal design and window placement are covered by the energy requirements rather than here — see Energy efficiency and sustainability in modular homes. No independent Australian research on the liveability of small secondary dwellings has been located for this guide, and none of the layout observations above should be read as based on measured post-occupancy evidence.

References §