How much does a single-storey extension cost in 2026?

Single-storey extensions typically cost between $2,000 and $4,000 per square metre. A mid-size 40 sqm extension runs between $80,000 and $160,000 depending on finishes, site access, and design choices. Simpler layouts with standard materials sit at the lower end of that range.

How much does a two-storey extension cost compared to a single-storey?

Two-storey extensions cost roughly $3,000 to $5,500 per square metre compared to $2,000 to $4,000 for single-storey builds. The premium reflects structural engineering, scaffolding, and temporary roof work. A full second-storey addition can range from $150,000 to $350,000 or more.

Do I need council approval for a home extension?

Yes. Both single-storey and two-storey extensions require a building permit. A planning permit may also be needed if the project affects neighbouring properties' sunlight, privacy, or breaches setback limits. Second-storey additions face stricter scrutiny for height and overshadowing.

Can I stay in my house during a two-storey extension?

In many cases, no. Roof removal and structural work on a second-storey addition often require temporary relocation, especially during the framing and weatherproofing stages. Single-storey extensions are less disruptive, and most families can stay home throughout the build.

What is the ROI on a second-storey addition?

National averages for 2026 put the ROI on a well-designed second-storey addition at 50-70% of the total project cost. Homes in space-constrained suburbs tend to see returns at the higher end of that range because buyers pay a premium for added floor area without sacrificing outdoor space.

Is it cheaper to build out or build up?

Building out is almost always cheaper per square metre. But the per-square-metre comparison is misleading. A two-storey extension shares one foundation and one roof across two floors, which means the cost per additional room can sometimes favour going up, especially on tight blocks where extending outward isn't possible.

How long does a home extension take to build?

A single-storey extension typically takes 3 to 5 months from start to finish. Two-storey builds run 5 to 8 months due to structural complexity, longer council approval timelines, and the additional construction phases involved in roof removal and upper-floor framing.