Can I build a granny flat on my block?

Many residential blocks can take one, but the block has to allow it before anyone pays for a design. The zone has to permit a second dwelling, the lot has to hold it with open space and parking for both, and the services have to reach it. Where the existing house sits often settles it. A house in the middle of the lot leaves little room either side, while one near the front leaves the back yard open.

What decides whether it fits?

The zone decides whether a second dwelling is allowed at all, and in some places whether it can be let to someone outside the family. Then there is the lot itself. Some places set a lot size below which a granny flat is not allowed, and a narrow or steep block can rule out the spot you had in mind. Last come the overlays. Flood, bushfire, heritage and character overlays can each add a planning question, and a flood overlay can decide where on the lot the flat may go. The post on flood overlays explains what that mapping changes.

What about the services?

A granny flat needs water, sewer and power, and the sewer is the one that catches people out. The flat’s drain has to reach the main with enough fall, and a flat built over or near a sewer main needs the water utility’s consent first. An easement across the back of the lot can take the space you planned to build on, and the post on building over an easement explains what that involves.

Who decides?

The council decides whether the flat can go on the lot, or the state where it runs its own path for second dwellings, and a certifier or the council gives the building approval. The water utility decides anything near its mains.

What goes on the site plan?

The plan shows the existing house as it stands and the flat at its real size where it will sit, with the distance between them and to every boundary. It marks the private open space and the parking, the easements and the sewer, and the site cover across both dwellings. It is the sheet that shows whether the flat fits before anyone draws a floor plan.

Reading it for your own lot

RapidSiteplan reads the lot from its address in a minute: the boundaries, the house traced from the aerial photo, the zone where it is mapped, the overlays, and the sewer, water and drainage under the yard. Place the flat and the sheet shows the separation, the open space and the site cover of both dwellings as you move it. The granny flats page shows the sheet, the post on how big a granny flat can be covers the floor area cap, and the council pages for every state show what each council maps. Start with the address. The post on whether granny flats need council approval covers the approval in each state.

Common questions

Can I build a granny flat on my block? Often, if the zone allows a second dwelling and the lot can hold it with open space, parking and the distance from the house the council asks for. The sewer has to reach it, and easements and overlays can move the spot or rule it out. The council decides, from a site plan with both dwellings on it.