Ground-Floor Extension Ideas & Costs

Most people start thinking about a ground-floor extension when the house stops fitting the family. The kitchen feels tight, there is nowhere for everyone to sit together, and moving would cost more than it is worth once you add stamp duty and agent fees. Building out into your block is often the simplest fix, and around Wollongong and the Illawarra it is one of the jobs we get asked about most.

Here is a plain rundown of the main types, what they roughly cost, and how to work out whether going out beats going up.

Rear extensions

Pushing the back of the house out into the yard is the most common move, and usually the easiest to picture. It is what most people mean when they say they want to open up the kitchen, dining and living into one connected space that flows out to the backyard.

A rear extension works well because you are building onto the part of the house you use most, and you can often keep living in the home while it goes ahead. On a flat block it is fairly straightforward. Plenty of blocks through the Illawarra sit on a slope, and that changes things, you may need extra footings, retaining or a raised floor, which adds cost and engineering. Worth knowing early rather than at framing stage.

Side and wrap-around extensions

A side extension uses the strip of land beside the house. It suits a narrow room you want to widen, an extra bedroom, a study, or a bigger bathroom. The main thing to check is your side setback, the required gap between the wall and the boundary, because that often decides how much room you actually have to play with.

A wrap-around does both, extending along the rear and one side around a corner of the house. It gives you the biggest change to how the home lives, and it is the most involved of the three. More new roof, more wall, and usually more work tying the addition back into the existing structure. It costs more for the same reason it delivers more.

What a ground floor extension roughly costs

Cost depends on size, finishes, your site and how much of the existing house you disturb. As a rough guide, a straightforward ground-floor extension often lands somewhere around $3,500 to $6,000 per square metre, and it can sit higher once you add a new kitchen, bathroom, a sloping site or high-end finishes.

Treat that as a starting point, not a quote. The things that push it up or down are:

• Size and shape, a simple square addition costs less per square metre than a complex footprint
• Kitchens and bathrooms, wet areas carry more plumbing and fit-out cost than a plain room
• Your site, slope, access, drainage and connecting to the existing roofline all add up
• Finishes, flooring, joinery and glazing can swing the number a long way

The honest answer is that a home extension covers a wide range, and the only way to get a real figure is to price your actual plans. That is what a fixed-price proposal is for.

When going out beats going up

The usual alternative is a second-storey addition. Both are good options, they just suit different blocks and budgets.

Building out on the ground floor is often the better call when:

• You have the yard to spare and do not mind trading some of it for floor space
• You want to avoid strengthening the existing structure, since going up often means upgrading footings and walls to carry the new load
• You would rather stay living in the house through most of the build

Going up tends to win when your block is tight, when you want to keep the whole backyard, or when the views are worth chasing from a first floor. It usually costs more per square metre and more often means moving out for part of the build. Neither is automatically right, it comes down to your block, how you want to live, and the number you are comfortable with.

Approvals for your block

Some extensions can go through as complying development (CDC), which is a faster certifier-approved path when the work fits set rules. Larger or more complex ones need a development application (DA) through council. Which path applies depends on your zoning, setbacks, and how much you are adding.

Rules vary between council areas across the Illawarra and the Southern Highlands, so confirm the path for your own block with your local council or a private certifier before you lock in a design. It is far cheaper to know the constraints before drawings than after.

If you are weighing it up, the simplest place to start is a rough sketch of what you want and an honest chat about what your block will allow. From there the numbers stop being a guess.