How Much Does It Cost to Put an Extension on a House in New Zealand?

Adding an extension to your house in New Zealand isn’t just about more space-it’s about making your home work better for your life. Maybe you need a bigger kitchen for family dinners, a home office that doesn’t feel like a closet, or a spare bedroom for aging parents. But before you start dreaming about sunlit rooms and open-plan living, you need to know: how much does it cost to put an extension on a house? The answer isn’t simple. It depends on where you live, what you’re building, and who’s doing the work.

What’s the average cost of a house extension in New Zealand?

In 2025, a basic single-storey extension in New Zealand runs between $3,000 and $5,000 per square metre. That means a 20-square-metre addition-roughly the size of a small living room-could cost anywhere from $60,000 to $100,000. This includes materials, labour, permits, and basic finishes like flooring, paint, and lighting. But this is just the starting point.

Costs climb fast if you’re in Wellington, Auckland, or Christchurch. Land is expensive, labour is in short supply, and building materials have stayed high since the supply chain disruptions of 2022. A high-end extension with premium finishes-like European cabinetry, underfloor heating, or smart home tech-can easily hit $7,000 per square metre. That same 20-square-metre room? Now it’s $140,000.

Two-storey extensions cost more than single-storey ones-not because they’re bigger, but because they require stronger foundations, more structural steel, and complex scaffolding. Expect to pay 15-25% more than a single-storey build for the same floor area.

What’s included in the cost?

Many people think the quote they get from a builder covers everything. It doesn’t. Here’s what you’re actually paying for:

• Design and plans: A registered architect or building designer charges $1,500-$5,000 to draw up plans and get them approved by the council. If you need a structural engineer (common for extensions over 30m²), add another $1,000-$2,500.
• Building consent: Council fees vary, but for a typical extension, expect $2,000-$4,000. This covers the cost of checking your plans meet the Building Code.
• Labour: This is the biggest chunk. A skilled builder in Wellington charges $60-$85 per hour. For a 6-8 week project, that’s $20,000-$40,000 just for people showing up and doing the work.
• Materials: Timber, insulation, windows, roofing, plumbing, electrical-these add up. A basic extension uses around $1,500-$2,500 per square metre in materials alone.
• Finishes: Tiles, cabinetry, lighting, taps, and flooring are separate. Budget $10,000-$25,000 if you want quality. Skip these and you’ll end up with a cold, unfinished box.
• Contingency: Always add 10-15% for surprises. A hidden rotten floor joist, a pipe you didn’t know ran under the patio, or a delay in window delivery can blow your budget fast.

What type of extension gives you the best value?

Not all extensions are created equal. Some give you more bang for your buck.

Kitchen extensions are the most popular-and often the most cost-effective. Kitchens are high-value spaces. A well-designed one can boost your home’s resale value by 60-80% of what you spend. Plus, you use it every day.

Home offices are rising fast. With remote work still common, a quiet, dedicated space adds practical value. A 12m² office with good lighting and insulation costs around $40,000-$60,000. That’s less than a full kitchen extension, but still adds serious livability.

Second-storey additions are expensive, but they’re the only option if you’re on a tight block. You don’t lose your backyard, and you gain views. But they require deeper footings, temporary supports, and often a full rewire. You’re paying for complexity.

Garage conversions are the cheapest route-if your garage is attached and already has a solid foundation. Turning it into a living space cuts out foundation and roofing costs. You’ll still need insulation, windows, plumbing, and consent, but you can do it for $30,000-$50,000.

How do council rules affect the cost?

Every council in New Zealand has its own rules. In Wellington, you can’t build an extension higher than 3.5 metres if it’s within 1.5 metres of a boundary. In Auckland, you might need a resource consent if your extension blocks a neighbour’s view. In rural areas, you might need a water supply consent if you’re adding a bathroom.

These rules don’t just slow things down-they add cost. If your design doesn’t fit the rules, you’ll need to revise it. That means more design fees, more council fees, and more delays. One client in Karori spent $8,000 extra because their original plan blocked a neighbour’s sunlight. The council demanded a redesign. They lost six weeks.

Always check your local council’s District Plan before you start. Many have online tools to check what’s allowed. Don’t assume your builder knows the rules. Ask for proof they’ve checked.

Can you save money without cutting corners?

Yes-but not by hiring the cheapest builder or skipping permits.

Here’s how real homeowners in Wellington save:

• Time your build for winter: Builders are quieter from May to August. You might get a 5-10% discount on labour.
• Buy materials yourself: If you’re handy, buy windows, tiles, or lighting online. You can save 20-30% compared to letting your builder source them.
• Use standard sizes: Custom windows, doors, and cabinetry cost more. Stick to common dimensions-like 900mm wide doors or 600mm kitchen cabinets.
• Do some prep work: Clear the site, remove old decking, or demolish a shed yourself. Labour for demolition is $50-$100 per hour. Do it yourself and you save thousands.
• Choose a simple roof: A gable roof is cheaper than a hip or butterfly roof. A flat roof sounds modern but leaks more often and costs more to waterproof.

What are the hidden risks?

Most people worry about going over budget. The real danger is ending up with a house that doesn’t feel like yours.

One common mistake? Building an extension that doesn’t match the original house. A 1980s brick home with a shiny glass box attached looks like two different houses. It kills curb appeal and can hurt resale value.

Another? Ignoring thermal performance. New Zealand homes are cold. If your extension isn’t properly insulated, you’ll pay more in heating bills than you saved on the build. Use at least R-2.6 insulation in walls and R-4.0 in ceilings. Double-glazed windows are non-negotiable.

And don’t forget access. A new kitchen extension might block your back door. A second storey might cut off light to the downstairs bathroom. Walk through your house with a tape measure and a friend. See how the new space connects to the old.

Should you DIY your extension?

Unless you’re a licensed builder, don’t.

Building consent requires a registered professional to sign off on structural and electrical work. You can’t legally do plumbing or wiring yourself unless you’re certified. And if you try to save money by doing it anyway, you’ll hit a wall when you sell. Buyers won’t buy a home with unpermitted work. Insurers won’t cover it.

There’s one exception: if you’re a licensed builder and you’re doing it for yourself. Even then, most pros hire out the complex parts-like foundation pouring or roof framing-because it’s faster and safer.

How long does it take?

From design to move-in, a typical extension takes 4-6 months.

• Design and consent: 4-8 weeks
• Prep and demolition: 1-2 weeks
• Building: 8-12 weeks
• Finishes and inspections: 2-4 weeks

Delays happen. Weather in Wellington is unpredictable. Materials get stuck in shipping. Inspectors are backlogged. Build in a 2-4 week buffer. If your builder says it’ll take 8 weeks flat, they’re not being honest.

What’s the return on investment?

On average, a well-executed extension adds 70-100% of its cost to your home’s value. A $80,000 kitchen extension might add $75,000 to your sale price. That’s not profit-that’s recovery. You’re not getting rich, but you’re not losing money either.

Some extensions do better. A second bathroom in a three-bedroom home? That can add 120% of its cost. A home office? If it’s well-designed and marketed, it can boost value by 80-110% in today’s market.

But here’s the catch: the return only matters if you plan to sell. If you’re staying for 10+ years, focus on comfort, not resale. Your home should work for you-not the next buyer.

Final thoughts: Is it worth it?

Putting an extension on your house is a big decision. It’s messy, expensive, and stressful. But it’s also one of the smartest ways to upgrade your life without moving.

If you’ve lived in your home for years and love the neighbourhood, the school zone, the backyard-it’s worth it. You’re not just adding square metres. You’re adding years to your time in a place you already love.

Start with a clear goal. Don’t just say ‘more space.’ Say: ‘I need a kitchen where the whole family can cook together.’ Or: ‘I need a quiet room to work without the kids shouting.’ That clarity will guide every decision-from the builder you pick to the windows you choose.

And always, always get at least three quotes. Don’t pick the cheapest. Pick the one that makes you feel confident. Ask for references. Visit their past work. Talk to the homeowners. If they say, ‘They were late, but the finish was perfect,’ that’s better than a quote that’s $10,000 lower but comes with silence.

Extensions aren’t cheap. But for many families in New Zealand, they’re the best investment they’ll ever make in their home.