How much does a house extension cost in New Zealand?

There’s no one-size-fits-all when it comes to house extensions. Some are modest home office extensions, while others are comprehensive self-contained flat extensions. That’s why providing an accurate, all-encompassing cost estimate is impossible. However, there are a few things most house extensions have in common and these also have the biggest impact on the final cost: the size of your extension, the exterior and foundation, council consent, and your home’s existing layout. 
In this article, we’ll give you a detailed run-down of how exactly these main budget drivers affect the cost of building a house extension. Your personal priorities will dictate the cost of your house extension but this information will help you understand where you may need to compromise to stay on budget and where you can afford to splurge. 
Working with a Refresh Renovation Consultant is by far the most effective way of obtaining an accurate quote for your specific house extension project. But, if you’re not ready to take the plunge and simply want to learn more, we’ve provided real-life examples complete with actual costs so that you can compare your goals with what can be achieved at different price points. 

Main budget drivers

• Size of your extension
• Exterior and foundation
• Council consent
• Layout of your existing home 

Read on to find out how much your house extension may cost depending on the changes you are looking to make.

Size of your extension

While the obvious assumption is larger extensions are more costly, the reality is that smaller house extensions may work out slightly more expensive per square metre than larger ones, as many of the overheads, such as council permits, stay the same. However, the materials cost for a large renovation will almost always exceed that of a smaller but comparable project. 
Regardless of the size of your house, there are still plenty of cost-effective ways to execute a house extension. This 78m2 project was completed for only $75,000* (OCT 2021) thanks to a smart solution of enclosing unused exterior space to extend the living area, thus creating a large extension for a relatively modest price. 

Exterior and foundation

Dreaming up the fabulous interior of your house extension is one of the best parts of the process, but you can’t forget how it will look from the outside. An extension doesn’t need the same cladding as the main property; however, it should be cohesive. And if you do prefer continuity for your home's exterior, be prepared to pay a significant amount if the existing cladding is high-end or not easy to source. 
Though cedar is an expensive material, it ages well aesthetically and has a lifespan that can exceed 35 years. See how this single-bedroom extension was beautifully blended into the main property using cedar cladding for $88,000*. (JUN 2019)
If your property was built on a sloping plot or the substratum is unsuitable for additional construction, it’s likely that your project will include excavation and groundwork. It could also require a new foundation, all of which will add to the overall cost.  
At 44m2, this extension wasn’t oversized; however, the extensive groundwork required to embed the necessary timber retaining wall drove the final price up to $290,000*. (JUN 2021) It was worth it in the end as the homeowner ended up with two additional bedrooms, a new bathroom, and extra laundry space. Read the full story here. 

Council consent

Building applications, resource consent, inspections, and other council requirements add up quickly. Depending on the project and what’s needed, council-related costs can run anywhere from a few hundred dollars well into the thousands. Fees and charges for your local council should be listed on their website so you can get an initial idea of the likely expense.
While reviewing a change of cladding application for this granny flat extension (approximately 60m2), the council deemed a firewall necessary between the proposed extension and the main house, which increased the overall cost to $294,000*. (JUN 2022)

Layout of your existing home

Reconfiguring your home’s existing layout - removing or adding walls, windows, or doors - to accommodate the extension will be more costly than if you were to just build an abutting structure. However, it could prove to be a worthwhile investment if it creates opportunities that didn’t exist previously, such as adopting an open-plan layout or creating indoor/outdoor flow. Building a new bedroom at the rear of this family home required the entry door and porch to be relocated. See the dramatic $140,000* transformation here. (SEP 2019)

Outgrown your home and curious about the cost of an extension? 

Our comprehensive 5-step approach to renovations includes a thorough costing phase with a fixed quote specific to your project. You’ll know the cost before breaking ground. If you’re considering a house extension, we offer no-obligation consultations so you can discuss your ideas and goals with a professional. To arrange your free consultation, get in touch with a local Renovation Consultant today!
*Costs are shown as an indicative guide of what previous projects have cost. The price of renovating a home rises each year as material and labour costs increase. For an estimate/quote on your specific project, please consult your local Refresh Renovations Consultant to find out more about our planning, design and build process.
**All Refresh Renovations franchises are independently owned and operated.