The granny flat is part of the Australian vernacular, and stirs up images of squat buildings in oversized suburban backyards to accommodate ageing relatives or transient tenants. 

Today, the possibilities for these secondary structures are wide-ranging, with volume home builders and small- to medium-sized businesses alike offering stylish and spacious designs, and increased amenity through thoughtful details and clever storage options. The modern granny flat, whether attached or detached, custom-built or kit-style, is proving to be much more versatile than its namesake – but a big part of that comes down to where you live.

From a regulatory perspective, only South Australia calls them this. In NSW, Queensland and the ACT they’re known as ‘secondary dwellings’, while Tasmania and Western Australia refer to them as ‘ancillary dwellings’. Different still, Victoria names them ‘a dependent person’s unit’ and the Northern Territory ‘an independent unit’. No matter what you call them, the states and territories agree on one thing: they should provide an adequate level of amenity for the occupants, but should also not adversely impact on the amenities of the primary dwelling on the block or impact the occupants of adjoining properties. 

While each state or territory has subtly different approaches to achieving this, the reasons why people want to build a granny flat is generally consistent across the nation.

Firstly, family structures are changing. As Australia’s population continues to age, and grandparents live longer, it is becoming increasingly common for several generations to reside together, whether that is for cultural, lifestyle or financial reasons. With their smaller size and design versatility, granny flats give the occupants of a primary dwelling more living space and, in the case of detached buildings with a separate entryway, more privacy for the entire household. Grandparents have independence but proximity to the family, or if utilised as a ‘teenagers retreat’ or home office, middle-aged parents benefit from (much needed) peace and quiet. 

Secondly, the deterioration in housing affordability in Australia has been a natural driver in the increased interest and demand for granny flats. For young adults finding it difficult to break into the residential property market, these secondary structures are often a good means to bridge the gap between moving out of the traditional family home and purchasing their first home. Granny flats enable parents to provide their children with a ‘starting space’ while they save for a deposit, or they can serve as a viable option for senior citizens who want to downsize and use their primary dwelling as a rental.

When it comes to planning requirements for granny flats across the nation, there are a number of similarities and differences. Typically granny flats are permitted in residential zones in each state or territory with varying requirements based on total site area, maximum floor area/floor space ratio, as well as open space and car parking requirements for both the existing dwelling and the proposed granny flat. For example, granny flats generally cannot be built on lots smaller than 450 square metres. In NSW the total floor area of a secondary dwelling cannot exceed 60 square metres, in comparison to 70 square metres in WA or 80 square metres in Queensland. Size restrictions of floor area often varies council to council within each state or territory.

What is most interesting is that setbacks from boundaries based on (wall) height is not overly restrictive in terms of the planning assessment criteria. The reason for this could be that, at present, granny flats are usually offered only as a single-storey built form and therefore their height impact is relatively minimal – that is they create minimal overshadowing or opportunities for overlooking.

A granny flat would normally be considered a Class 1a building and would be required to meet the provisions of the National Construction Code (NCC) in relation to separation from boundaries and other buildings on the allotment i.e. fire separation. As with any dwelling, it is important to check the planning and building regulations in each state and territory to understand all the requirements that apply to a granny flat. You should also not assume that you can subdivide a property once you have ticked all the boxes to construct a granny flat. In most states they can be rented out but must remain part of the one property.

When it comes to building granny flats, NSW is in a league of its own. The state built more than two and half times as many of these dwellings in 2018 compared to second-placed Queensland and almost 10 times as many as Western Australia. What this suggests is that the planning approvals framework in NSW, and to a lesser extent in Queensland, is much more flexible in allowing this type of dwelling than other states and territories. 

Planning frameworks are the largest single determinant of the number of granny flats constructed in each state. Restrictive rules in Victoria result in a very low number of granny flats for a state of its size. If this type of dwelling is to become a viable housing option for our growing population and changing demographics, it is important that all states and territories adopt more conducive planning frameworks for their construction.

While granny flats are currently a rapidly emerging dwelling choice because of their versatility, affordability and ability to ad-dress changing family structures, other flexible housing options, such as multi-family dwellings, may offer an alternative to the granny flat in the future. Multi-family dwellings are a newer idea aimed at having one building to accommodate more than one generation living under the same roof. Multi-family dwellings are generally not supported by state planning regimes as they are seen as dual occupancies or other medium density types of homes, however a discussion of the merits of such a dwelling type is beginning to emerge and it may be that in the future grannies and the kids can all have their own space under one roof without the planning hassles.