A granny flat is one of the better-value things you can add to an Illawarra block, but the first question is always the same: what does it cost? The honest answer is that it's a wide range, and the reason it's wide is the whole point of this guide. Below we walk through what drives the price and give some rough figures, so you can read a quote and see where the money's really going.
A quick note before the numbers. Every block is different, prices move, and the only real figure is a proper quote on your site. Treat everything here as a rough guide, not a promise.
Rough ranges for 2026
As a rough guide, a custom-built granny flat in the Illawarra in 2026 generally lands somewhere between the low-to-mid hundreds of thousands, depending heavily on size, site and finish. To break that down by type:
- Studio (around 35 to 45 square metres): the most affordable option, with open-plan living and a kitchenette. Lower per-square-metre cost because there are fewer rooms and less to fit out.
- One-bedroom (around 50 square metres): a proper separate bedroom and a full bathroom, which suits most tenants and family members. A common middle ground.
- Two-bedroom (up to the 60 square metre limit): the most you can build as a secondary dwelling, and the highest cost, though the per-square-metre rate often improves at this size.
Those bands assume a complete, livable dwelling, not a base shell. What moves you up or down within them is everything below.
What drives the price
The block itself. This is the cost people don't see coming. A flat, easy site is cheap to prepare. A sloping block means engineered footings and sometimes a stepped or suspended floor, and possibly retaining, before you've framed a wall. A lot of lots around the escarpment have a fall on them, so it's worth getting the site assessed early.
Site access. If a concrete truck and trades can pull up close to where the flat's going, the build runs efficiently. If every load has to be barrowed down a narrow side passage or craned over the house to the back yard, that's extra days and dollars.
Services connections. Power, water, sewer and stormwater to a second dwelling are rarely simple. It comes down to how far the flat sits from the existing connections, whether the sewer's at the right depth, and whether your stormwater can take the extra roof. A tricky connection can be a real chunk of the budget 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 full stone benchtops and floor-to-ceiling tiling. The same footprint can carry a very different invoice depending on the fit-out you choose. Our granny flat designs page goes through the layout options.
The coast. Near the water you want coastal-grade materials, fixings and flashing that actually cope with salt air, and decent eaves to keep the weather off. Saving a little on the build envelope is the kind of thing that costs you in five years, so we don't recommend it.
Is there a granny flat price list?
No, and any builder who hands you one is quoting a box rather than a finished dwelling on your block. A granny flat price only becomes real once someone has looked at your ground, your access and where the services run, which is why the honest answer to "how much is a granny flat in Wollongong" is a range until then.
The reason is that two identical 60 square metre flats on two streets in the same suburb can be a long way apart on price before a wall goes up, entirely because of footings, access and the sewer connection. A price list can't know any of that.
What you can ask for instead is a quote that names what's included: design and engineering, the approval pathway and its fees, site preparation, all four service connections, and the finishes schedule. Which pathway your block ends up on changes both that fee and the timeline, and granny flat council approval in NSW explains the difference between the two. If those are in there as real numbers rather than provisional sums, you can compare it to anything.
We give a free, no-obligation quote for your block. It costs you a site visit and an hour.
Reading a quote properly
The single most useful thing you can do is compare quotes on a like-for-like basis. A cheap headline number with site works and services left as extras can easily end up dearer than a higher fixed price that includes the lot. Ask what's in and what's out, and make sure site preparation, service connections and approvals are actually costed.
This is exactly why we give a fixed-price proposal before any work starts. You get one number for the whole job, with the design, engineering and approval included, so there's no drip-feed of extras once the slab's down.
The takeaway
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.
If you want a real figure for your block, the only way to get one is a look on site. Have a read of how we approach the granny flat build, then call us on 0434 037 851 or use the contact page for a free, no-pressure quote.
Common questions
- What's the cheapest way to build a granny flat?
- A studio or one-bedroom on a flat block with easy access and a builder's-range finish is the most affordable path, because the small footprint, simple site works and standard fixtures all keep the cost down. The catch is that a too-tight design or a hard block can wipe out the saving, so it's worth costing properly before chasing the lowest number.
- Why are two granny flat quotes so far apart?
- Usually because they don't include the same things. One might be a base build with site works, services and finishes left as extras, while the other is a fixed price for the lot. Always ask what's in and what's out, and make sure site preparation and service connections are actually costed rather than buried as a provisional sum.
- Does a sloping block cost more?
- Generally, yes. A fall on the block means engineered footings and sometimes a stepped or suspended floor, plus possible retaining, before a single wall goes up. Plenty of Illawarra blocks slope, so it's normal work, but it does add to the cost, and it's one of the biggest reasons two otherwise similar jobs come in at different prices.
- Will a granny flat add value or income?
- Most owners build one for rental income, family accommodation, or both, and a well-built secondary dwelling can do both. The actual figures depend on your block, the rental market and how the work's done, so treat it as a real investment to plan rather than a guaranteed return.