Granny Flats & Ancillary Dwellings

A Granny Flat Still Has to Work as a Full Home, Just a Smaller One

It’s easy to treat a granny flat as leftover space. Whatever fits in the back corner of the block, facing whichever way the fence runs. That’s usually how you end up with a dark little box that technically complies but nobody actually enjoys living in.
We treat it as what it is: a full, self contained home on the same block as your own, just built to a tighter floor area. In WA, that generally means keeping the design within 70 square metres, though some councils set their own limit, so it’s one of the first things we check against your site. It also has to read as part of the property it sits on. Under the R-Codes, an ancillary dwelling’s roofline, materials and colours generally need to match the main house, whether it ends up attached, tucked under the same roofline, or standing on its own further back on the block.
None of that changes what actually makes it livable. Orientation, natural light, storage and a bit of separation from the main house still matter at this scale, arguably more than they do in a full sized home, since there’s less floor area to hide a bad decision. Who’s moving in shapes the brief just as much: parents wanting to be close without sharing a kitchen, an adult child staying home a little longer, a dedicated rental, or a studio for a home based business. Each of those wants a slightly different layout, even within the same floor area cap.
We’ve also worked through the parts of this that catch people out. On one rural block we designed for, the granny flat needed sewer treatment approval through the council’s Health department on top of the usual building approval, because the site wasn’t connected to mains sewer. It’s the kind of detail that’s easy to miss until it holds up your build, and exactly why we check services and site conditions before drawing anything.
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What a New Home Design Actually Involves

A granny flat or ancillary dwelling brings its own set of rules that a full sized new home doesn’t have to deal with:

  • Floor area limit: WA's general cap for an ancillary dwelling sits around 70 square metres, though some councils apply their own figure, so we confirm your site's actual limit before concept design starts.
  • Design matching: roof pitch, external materials and colours generally need to align with the main dwelling under the R-Codes, since the two are read as one property from the street.
  • Configuration: attached to the main house, built under its existing roofline, or fully detached elsewhere on the block. Each option changes access, privacy and how much of your yard is left over.
  • Separation and privacy: entry points, windows and outdoor space arranged so the granny flat and the main house each get their own outlook, not a shared view straight into each other's living areas.
  • Parking: an additional car bay is often required depending on your block's density coding, unless the site sits close to a train station or a high frequency bus route.
  • Site services: connection to existing power, water and sewer where the block is serviced, or a separate on-site treatment system and Health department approval where it isn't.
  • Approval pathway: a design that meets the R-Codes' deemed to comply provisions can often skip a full planning application and go straight to a building permit. One that doesn't needs a development application first.

Our Process

1

Site & Brief

A site visit to check your existing home's position, orientation and services, alongside a conversation about who's moving into the granny flat, how they'll use it day to day, and your budget.

2

Concept Design

A concept plan developed within your site's floor area limit, matched to the main house's roofline and materials, and positioned so both dwellings keep their own privacy, light and outdoor space.

3

Design Development & Approval Pathway

The concept is refined with you while we confirm whether the design qualifies as deemed to comply. If it does, documentation moves straight toward a building permit. If it doesn't, we prepare and lodge a development application first.

4

Working Drawings & Permit Documentation

Construction-ready working drawings, plus building permit documentation (certified BA1 or uncertified BA2), and any Health department approval needed for an unsewered site. From here, it's handed to your builder for pricing.

What's Included

Granny Flats & Ancillary Dwellings

Design & Documentation

  • Site assessment covering your existing home's position, orientation and services
  • Concept design built within WA's ancillary dwelling floor area limit
  • Design matched to the main dwelling's roofline, materials and colours
  • Attached, under-roofline or fully detached configuration options
  • Design development through to construction-ready working drawings

Approvals & Coordination

  • Deemed to comply assessment, or a full development application where required
  • Building permit documentation (BA1 certified or BA2 uncertified pathway)
  • Council Health department approval for on-site sewer treatment on unsewered blocks
  • Coordination with structural engineers and other consultants where needed
  • Liaison with your builder through documentation and pricing
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RESIDENTIAL DESIGNS

New homes, subdivisions and granny flats, designed and documented end to end.

Questions? You’re covered.
How big can a granny flat be in WA?
Around 70 square metres is the general limit most councils apply, though some set their own figure. We check your specific council's requirement against your site before concept design starts.
Generally, yes. The R-Codes expect an ancillary dwelling's roofline, materials and colours to align with the main house, since councils read the two as one property from the street.
Yes. It can be rented out on its own even though it stays on the same title as your main dwelling. That's different from subdividing, where you'd end up with two separate titles instead.
It depends on whether your design meets the R-Codes' deemed to comply provisions. If it does, you can often go straight to a building permit. If it doesn't, a development application comes first. We confirm which pathway applies early.
No, not as it stands. A granny flat sits on the same title as your main dwelling, so it isn't a separate lot you can sell on its own. If a separate title is what you're after, that's a subdivision, which is a different process we also handle.
Attached shares a wall with the main house. Integrated sits under the same roofline without necessarily sharing internal access. Detached stands on its own elsewhere on the block. Each suits a different block shape and level of privacy.
Often, yes, one additional car bay, depending on your block's density coding. Blocks close to a train station or a well served bus route can sometimes be exempt.
Yes, but it usually needs its own on-site treatment system, approved through the council's Health department alongside your building approval. We've worked through this on a rural project before and factor it in from the site visit stage where it's likely to apply.
Sometimes, depending on your block size and R-Code, though it's worth raising at the first site visit rather than assuming. Building a granny flat now doesn't rule out subdivision later, but it can change what a future subdivision looks like.
A rough idea of who's moving in, how they'll use the space, and your budget is enough to start. Details of your existing home's services (power, water, sewer connection) help too, but we can confirm most of that ourselves during the site visit.

Ready to Add a Granny Flat to Your Block?

Start with a conversation about your site, your family and your budget.

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