Granny flat foundations are engineered screw piers installed directly in your backyard, wound below the reactive-clay movement zone and proof-tested by torque as they go in. Most granny flats are piled in about a day, with no bobcat cutting trenches through an established garden and no concrete cure time holding up the build. Core Screw Piling installs granny flat and secondary dwelling foundations across the Gold Coast, Brisbane and the Sunshine Coast up to Noosa. For the method itself, see our guide to what screw piling is and how it works.
What granny flat foundations need
A granny flat is a genuine dwelling, not a shed, so its footings need the same engineering rigour as a house: a design from a registered professional engineer (RPEQ) matched to your soil conditions, torque-verified installation, and certification your building certifier can act on. The difference is where the site sits: almost always a backyard, close to the existing home, with the owners still living in the front house throughout the build.
That combination, real structural loads plus a tight, lived-in site, is exactly where screw piles outperform dug footings. There is no trench to collapse in wet weather, no spoil heap sitting on the lawn for a week, and no risk of a concrete truck chewing up the driveway.
Why screw piles suit granny flats particularly well
- Compact machinery. Our installation plant fits through standard side access, so we rarely need to touch fences or gates.
- Minimal disturbance. No excavation through the existing garden, pool surrounds or established trees.
- Same-day build-on. Floor framing or slab work can usually start the day after piling finishes.
- Certified paperwork. Torque and depth records support the engineer's installation certification (Form 43) your certifier needs before framing continues.
- Sloped rear yards handled. Most granny flats end up on the back third of the block, often the part with the most fall. Screw piles are engineered for that from the start.
Queensland's planning reforms driving the granny flat boom
Queensland's 2022 planning reform removed the old occupancy restriction on secondary dwellings, meaning granny flats no longer have to house a family member to be legal. Councils across South East Queensland have continued relaxing the rules since: Moreton Bay Regional Council introduced a tiered gross floor area model in October 2024 that lifts the size threshold for smaller secondary dwellings, and similar easing has followed in other SEQ council areas.
The practical effect is a genuine granny flat boom across the region, and foundations are almost always the first trade booked once a design is locked in. If you are planning a secondary dwelling, check your specific council's current gross floor area and setback rules before finalising your design; the planning approval for the dwelling itself is separate from the footing method, and we can install to whatever design your approval requires.
The build sequence for a granny flat foundation
Tell us about the job
Send your plans, or a rough sketch and photos of the site, plus any soil report or engineering you already have.
Site assessment and quote
We review access, slope and soil conditions, arrange engineering if it is missing, and give you one clear price.
Installation
Piles are wound in with torque monitored on every one, typically finished within a day for a standard footprint.
Certification and handover
You get the torque records and engineer certification your certifier needs, ready for the next trade to start framing.
What granny flat foundations cost
Granny flat piling is priced on the same factors as any structural job: design load, founding depth, pile count and access. A typical granny flat needs more piles than a deck but far fewer than a full house slab, so per-project cost usually sits between the two. Our screw piling cost guide covers the full breakdown of what drives the price, and a quote for your specific footprint costs nothing to obtain.
Granny flat foundation FAQs
Will council approve a granny flat on screw piles?
Yes. Screw piles are a standard engineered footing system. Your building certifier needs the engineer's design (Form 15) and installation certification (Form 43), which we supply as part of every job. The planning approval for the secondary dwelling itself is a separate process from the footing method.
Do I need a soil report for a granny flat?
Almost always, yes, since a granny flat carries real structural and habitable loads. If you do not already have one, we can arrange it as part of the quoting process.
Can you get equipment into a tight backyard?
In most cases. Our compact installation plant is chosen specifically for standard side access and tight suburban blocks. Send photos of your access with your enquiry and we will confirm before you commit to anything.
How long does a granny flat foundation take to install?
Most standard granny flat footprints are piled within a single day. Larger footprints or difficult access can run longer, and we will give you a realistic estimate with your quote.
Does the sloped part of my backyard rule out a granny flat?
No. Sloping rear yards are one of the strongest cases for screw piles, since they avoid the benching and excavation a dug footing would need. See our QLD guide to sloping and difficult site foundations for more detail.