Sydney granny flat rules: floor area, lot size and the approval path

What counts as a secondary dwelling

A secondary dwelling is a self-contained home built on the same lot as an existing house, either as a standalone structure, attached to the main house, or converted from part of an existing building such as a garage. It needs its own kitchen, bathroom and living area, and is intended for separate occupation, whether that is family, a tenant, or a home office style arrangement with living facilities.

The rules that commonly apply

Under the Housing SEPP, secondary dwellings are commonly approved as complying development, subject to standards that include a maximum floor area, commonly cited as 60 sqm, and a minimum lot size, commonly cited as 450 sqm (check current limits with us, since these figures are reviewed and can change, and some council areas set out variations). The secondary dwelling must sit on the same lot as the principal dwelling, meet setback and height requirements, and generally cannot be subdivided separately from the main house.

There are other standards too, covering things like private open space, parking and landscaped area, which vary depending on your zone and lot. A quick site check against the Housing SEPP standards early in design will tell you whether your concept fits comfortably or needs adjusting.

The approval path: usually CDC

Most secondary dwellings that meet every Housing SEPP standard go through as a Complying Development Certificate (CDC), issued by a registered certifier rather than council. This is generally the faster path because it is assessed against fixed rules rather than a merits-based planning process, and complying development carries statutory assessment timeframes that give a working benchmark, though the exact timing still depends on how complete your application is when it is lodged.

If your design does not meet one of the standards, for example a slightly oversized floor plan or a lot just under the minimum size, CDC is not available for that scope and you would need a Development Application (DA) to council instead, followed by a Construction Certificate. This is not unusual, and does not mean the project cannot proceed, just that it goes through council's merit assessment rather than the complying development pathway.

Documents you will need

For a CDC application you generally need a Section 10.7 Planning Certificate from your council, current site survey, architectural or building designer drawings, and, depending on the site, a BASIX certificate and any specialist reports your certifier identifies as relevant (such as bushfire or flood assessments in affected areas). Your certifier will confirm the exact list once they have seen your site and drawings.

The process with Vast

Attached versus standalone granny flats

The Housing SEPP standards apply slightly differently depending on whether your secondary dwelling is a standalone structure at the rear of the block, attached to the existing house, or converted from an existing structure such as a garage or granage. A standalone build generally has more flexibility on placement but needs its own services connections and, sometimes, its own driveway access. An attached or converted design can be more cost effective but needs careful attention to fire separation and existing structural capacity if you are working within an older building. Your certifier and designer can talk through which approach suits your site and budget before drawings are finalised.

Renting out a secondary dwelling

Once approved and occupied, a secondary dwelling can generally be rented out separately from the principal dwelling, subject to the usual landlord obligations that apply to any rental property in NSW. It cannot be subdivided or sold separately from the main house, since the approval relies on both dwellings sitting on the one lot. This is worth keeping in mind if the long-term plan involves eventually splitting the title, since a secondary dwelling approval does not create two separately saleable properties.

Common issues we see

Key takeaways

If you are planning a granny flat in Sydney, our Granny flat certifier Sydney page covers the full approval and inspection process, and our CDC or DA post explains the two approval routes in more depth. Call our Sydney office on (02) 9821 2062 or get a free quote and we will check your plans against the standards before you spend money on detailed drawings.