The cost to build a granny flat in the Illawarra depends mostly on your block and how the flat is fitted out, rather than on the number of rooms. As a rough guide, a complete, custom-built granny flat generally sits somewhere in the low-to-mid hundreds of thousands of dollars, finished and livable. The real figure for your property only comes from a quote based on a site visit.
This page covers what sets the price and what a fixed-price proposal from Ovas Build includes. For a wider NSW overview, see our post on how much a granny flat costs in NSW.
How much does it cost to build a granny flat?
Price moves with three things: the size of the flat, the condition of the block and the level of finish. A larger flat on a hard site with a high-end kitchen sits at the top of the range, and a small flat on an easy site with builder's-range fixtures sits at the bottom. Every block is different and prices move, so treat any general figure as a starting point.
1 bedroom and 2 bedroom granny flat cost
Secondary dwellings in NSW are capped at 60 square metres of floor area (measured to the outer face of the external walls), so the main choice is how that space is used.
- Studio (around 35 to 45 square metres): open-plan living with a kitchenette and a bathroom. It has the lowest total cost because there are fewer rooms to fit out.
- One bedroom (around 50 square metres): a separate bedroom and a full bathroom, which suits most tenants and family members.
- Two bedrooms (up to 60 square metres): the largest you can build and the highest total cost, although the cost per square metre often improves at this size.
These all assume a complete dwelling and not a base shell. Our granny flat designs page shows the layouts for each size.
What changes the cost of a granny flat
The block. A flat, easy site is cheap to prepare. A sloping block needs engineered footings, sometimes a stepped or suspended floor, and possibly retaining. Many lots around the escarpment have a fall, so it pays to have the site assessed early.
Site access. If a concrete truck and trades can get close to where the flat is going, the build runs efficiently. If materials must be carried down a narrow side passage or craned over the house, it adds days and cost.
Service connections. Power, water, sewer and stormwater to a second dwelling depend on how far the flat sits from the existing connections, the depth of the sewer and whether your stormwater can take the extra roof. A difficult connection can take a large share of the budget on its own.
Size and finishes. A builder's-range kitchen and bathroom cost far less than stone benchtops and full-height tiling, so the same footprint can carry very different totals.
Coastal conditions. Near the water we use coastal-grade materials, fixings and flashing that cope with salt air, with eaves that keep the weather off.
The approval pathway. Whether the flat goes through as a complying development certificate or a development application changes the fees and the timeline. Our guide to granny flat council approval in NSW explains the difference.
Why there is no granny flat price list
A list price cannot account for footings, access or where the sewer runs on your block, and those are often what separate one quote from another. A quote that names what is included is more useful, so you can compare it with any other.
What our fixed-price proposal covers
Before any work starts we give a fixed-price proposal for your block. It names:
- design and engineering
- the approval pathway and its fees
- site preparation
- power, water, sewer and stormwater connections
- the finishes schedule
With these set out as real numbers rather than provisional sums, there are no extras after the slab is down. A cheap headline price with site works and services left out can end up dearer than a higher fixed price that includes them. If you are weighing a prefabricated option, see what a granny flat kit price actually covers.
Get a cost for your block
We visit the site, look at the slope, access and services, and come back with a fixed price. Read how we approach the granny flat build, then call us on 0434 037 851 or use the contact page to arrange a quote.
Common questions
How much does a granny flat cost to build in NSW?
A complete, custom-built granny flat generally sits somewhere in the low-to-mid hundreds of thousands of dollars, finished and livable. Where yours lands depends on the size, the block and the finishes. The only reliable figure comes from a quote based on a site visit.
How much does a 1 bedroom granny flat cost compared with a 2 bedroom?
A one-bedroom of around 50 square metres costs less than a two-bedroom, which can go up to the 60 square metre limit. The two-bedroom costs more in total, though the cost per square metre often improves at that size. The block and the fit-out can move either price more than the extra bedroom does.
Is there a granny flat price list?
No. A price list prices a box, and a granny flat only has a real price once someone has looked at your ground, your access and where the services run. Two identical flats on two streets in the same suburb can differ a long way before a wall goes up.
Why are two granny flat quotes so far apart?
Usually they do not include the same things. One may be a base build with site works, services and finishes left as extras, while the other is a fixed price for everything. Ask what is in and what is out, and check that site preparation and service connections are costed rather than held as a provisional sum.
Does a sloping block cost more?
Generally yes. A fall on the block means engineered footings, sometimes a stepped or suspended floor, and possibly retaining, before the walls go up. Many Illawarra blocks slope, so it is common work, and it is one of the main reasons similar flats are priced differently.
What does a fixed-price granny flat proposal include?
Ours names the design and engineering, the approval pathway and its fees, site preparation, the service connections and the finishes schedule, so you get one number for the whole job. You can compare it against any other quote line by line.