It's the first question almost everyone asks, and it's a fair one. A granny flat is a real investment, and you want a number before you get attached to the idea. The honest answer is that a granny flat in NSW covers a wide range, and the reason it's wide is the whole point of this post. Two flats that look the same on paper can land thousands apart once you factor in the block they're going on.
We build granny flats across Wollongong, the Illawarra and the Southern Highlands, and we get asked about cost most weeks. Usually it's someone who's seen a kit advertised cheap, then a builder quoted them a lot more, and they want to know who's right. Often both numbers are honest. It comes down to what's actually in the price, and what your block does to the job once you start digging.
Rough ranges for 2026
As a rough guide, a complete, custom-built granny flat in NSW in 2026 generally sits somewhere in the low-to-mid hundreds of thousands of dollars, finished and livable. Broken down by type:
- A studio, around 35 to 45 square metres, is the most affordable. Open-plan living, a kitchenette and a bathroom, with fewer rooms to fit out.
- A one-bedroom, around 50 square metres, with a separate bedroom and full bathroom, sits in the middle and suits most tenants and family members.
- A two-bedroom, up to the 60 square metre limit, is the dearest in total but often the best value per square metre.
A budget kit dropped on a flat block with basic finishes lands at the lower end. A custom build with a proper kitchen and bathroom, on a site that needs real preparation, lands at the upper end. Every block is different, so treat these as a starting point, not a quote.
What actually moves the number
Here's where the real variation lives, in roughly the order it bites:
The block itself. This is the cost people don't see coming. A flat, easy site is cheap to prepare. A sloping block, and plenty around the escarpment have a fall on them, means engineered footings and sometimes a stepped or suspended floor, occasionally retaining, before a single wall goes up. This is different on every site, and it's the number one reason two quotes diverge.
Access. If a concrete truck and trades can get close to where the flat's going, the build runs smoothly. If every load has to be barrowed down a tight side passage or craned over the house to the back yard, that's days and dollars you won't get back.
Services. Power, water, sewer and stormwater to a second dwelling are rarely simple. How far the flat sits from the existing connections, whether the sewer's at the right depth, whether your stormwater can take the extra roof, all of it adds up. A messy connection can run into five figures on its own.
Size and finishes. A studio costs less than a two-bedroom, and a builder's-range kitchen and bathroom cost a fraction of stone benchtops and full-height tiling. The same footprint, a very different invoice.
There's one more that matters in NSW coastal areas especially. Salt air. Near the water you want exterior materials, fixings and flashing that cope with it, and decent eaves to keep the weather off. Saving a little on the build envelope is the kind of thing that bites you in a few years.
Why a cheap quote can cost more
The trap with granny flat pricing is comparing a headline number that isn't comparing the same thing. A low base price with site works, services and finishes left as extras can easily end up dearer than a higher fixed price that includes everything. Always ask what's in and what's out, and make sure the site preparation and the service connections are properly costed, not buried as a provisional sum that balloons later.
This is exactly why we give a fixed-price proposal before any work starts. You get one number for the whole job, design, engineering and approval included, so there's no drip-feed of extras once the slab's down.
CDC or DA, and why your budget cares
The approval path sets your timeline and a chunk of your cost. Most granny flats in NSW go through as a Complying Development Certificate, a faster path where a private certifier signs it off without a full council assessment, often in around 20 days. If your site doesn't comply, it's a DA through council, which takes longer and costs more in fees and reports. Worth finding out which path you're on before anything else.
The takeaway
Want a single rule of thumb? Budget realistically, get the site assessed early, and don't choose on the headline figure alone. A granny flat that's costed properly and built once, with materials that suit the coast, is far better value than a cheap one that needs fixing.
For a fuller breakdown by size and site, see our granny flat cost guide. When you want a real figure for your block, the only way is a look on site. Read how we run the whole granny flat build, then call us on 0434 037 851 or get in touch through the contact page for a free quote.
Want a hand with this at your place? Get a free quote or call 0434 037 851.