How much does a home extension cost in NSW in 2026?

AuthorCorey PublishedJuly 2026 Read6 min read

Extensions are more expensive per square metre than internal renovations because you are adding structure, roof and services. The good news: an extension is often the highest-value move a homeowner can make on the block they already own, especially on the Central Coast where established suburbs have limited greenfield alternatives.

2026 NSW extension cost bands

Ground-floor extension

$150,000 to $400,000 depending on size, structural approach and finishes. Most rear-of-house additions we build on the Central Coast land in the $200,000 to $300,000 range.

First-floor addition

$250,000 to $600,000. First-floor additions carry a higher per-square-metre cost because of the structural work: reinforcing the existing structure, sometimes new pad footings, a staircase, and roofing tie-in.

Renovation combined with an extension

$500,000 and up depending on the renovation scope on the existing footprint plus the extension size.

Small studio, garage conversion or granny flat

$140,000 to $260,000. These often feel like extensions but are usually classified separately for approvals.

What drives the numbers

Structural strategy. Whether you can suspend, cantilever or need full pad footings changes cost substantially.
Roof tie-in. Matching an existing roof form seamlessly costs more than a flat-roof addition, but often reads better and adds value.
Services. Bringing bathrooms, kitchens or laundries into an extension adds plumbing, electrical and ventilation.
Windows and glazing. Large glazed openings are a major cost lever but often the highest-value element for natural light.
Site access. Steep, tight or difficult access sites add labour costs.
Coastal materials. Salt-air-rated fixings and finishes near the water add cost.

What is usually excluded from an extension quote?

DA lodgement fees, Section 7.12 contributions and certifier fees.
Architect or draftsperson fees (unless you have engaged us to run the design phase).
Landscaping, driveway extensions and external paving beyond what is required for the build.
Furniture and window furnishings.

Getting a real number

The most useful thing we can offer at this stage is a free consultation and a directional cost read based on your home and brief. Once plans and engineering are in hand, we return a detailed, fixed-price quote. From there you know exactly what you are signing up for.

Want a fixed-price extension quote?

Tell us about your home and what you want to add. A real person will reply in writing within one business day.

Enquire now

Frequently asked

Your questions, answered.

$250,000 to $600,000 depending on size and structural scope. The upper end reflects larger footprints, complex structural reinforcement of the existing home, and premium finishes.

Usually, yes. Ground-floor extensions avoid the structural reinforcement and staircase cost of a first-floor addition. They also let you keep living in the home more easily during construction. That said, planning constraints or block geometry sometimes force the decision.

Almost always, when done well. Established Central Coast suburbs like Terrigal, Bateau Bay, Wamberal and Erina have limited land supply and strong demand, so adding usable space to an existing home typically returns more than the cost of construction over the medium term.

Ours always are. Fixed-price contracts protect both sides and force careful pre-construction thinking. Some builders quote cost-plus for extensions, which can suit specific cases but leaves the homeowner exposed to cost drift.