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How Much Will it Cost to Build a 70 sqm Granny Flat?
- Bill Zhao
- Dec 10
- 3 min read
When it comes to doing any sort of renovation, build, or extension, the first thought on everyone’s mind is “What’s it gonna cost?” With the new 70m² granny flat rules being slated for rollout in early 2026, building a granny flat might be quite the viable option, bringing both space and value to your home. Here’s how much you’ll be looking at for a full-sized granny flat.
Cost to Build
Per square metre, a secondary dwelling typically costs around $3000 to $5000, which means a 70m² granny flat can cost around $225,000 to $375,000. This can vary depending on the materials used, the complexity of the design, and how difficult the site is. Ground conditions such as the soil, slope, and susceptibility to flooding can make it more expensive to work on than a traditional flat surface, adding tens of thousands in the process. If you’re looking for a custom built flat with many tailor-made features, it’ll also fetch a dearer price, especially when compared to pre-designed arrangements.
Getting Value
The actual value of building a granny flat, however, can depend greatly on how much it boosts the property. If you’re looking to rent it out for example, you can recoup some of the costs through passive income and reap the benefits when it’s time to live in. Some homeowners opt to rent out the main home instead for better rates while they move into the new granny flat.
Home Cohesion
It isn’t the granny flat alone that determines its value. Your main home and surrounding area have a big say in how much or how little it can add. In order to maximise the value gained from your new granny flat, your main home should be in good condition, without a jarring disparity in aesthetic. While visual harmony doesn’t affect the performance, having good cohesion can make it pass the eye test a lot easier. If it feels inferior to the main unit, buyers not be willing to pay as much. Likewise, if the main home is seriously showing its age, the area and property may appear undesirable.
Cost Saving from New Regulations
The 2026 housing rule change to granny flats formally allows their construction without the need for building or resource consent, so long as it remains under 70 sqm and meets basic criteria, which you can learn about here. The building consent itself can cost over $4500, which can worsen if multiple revisions or submissions are required. Not only does this rule change save you the upfront cost, but it also creates peace of mind against revisions eating away your time and money. A stressful building experience can leave a sour taste in your mouth when completion finally comes around.
You can find out more about Building consent fees and charges here
Intergenerational Living
If you’re particularly close with your family and are too attached to see them live far away, a granny flat could be the answer to saving you money from buying a second home. With Auckland becoming increasingly dense, intergenerational housing is turning into more and more of a preferred choice. This allows you to keep your loved ones close while saving money on property costs.
While on the surface, a few hundred thousand nets you a standalone granny flat with all household amenities, much of the value can be hidden away unless you look for it. With changes to build cost and land value all happening across next year, there’s a lot to look forward to if you’re in the market for a backyard home.
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