What the Granny Flat Cost Calculator Estimates
A granny flat (also called a minor dwelling or secondary dwelling) is a small self-contained home, usually built on the same section as an existing house. This calculator estimates the full cost of getting one built, not just the headline construction price. It combines four parts: the build cost (your floor area multiplied by a rate per square metre), site preparation and services connections, design and project costs, and council development contributions. The result is the all-in cost and the effective cost per square metre.
The 70m2 Consent-Free Exemption (from 15 January 2026)
From 15 January 2026, New Zealand's Building Act exemption schedule allows a single-storey, detached, self-contained dwelling of up to 70m2 to be built without a building consent or resource consent, provided it meets the criteria and the work is carried out or supervised by a Licensed Building Practitioner (LBP). The aim is to make it faster and cheaper to add a granny flat to a property, easing housing pressure and supporting multi-generational living.
Crucially, consent-free does not mean rule-free. The building must still comply with the Building Code in full, you still pay development contributions to your council, and you must still satisfy your title (any covenants or easements) and the Resource Management Act, including district plan rules on setbacks, height, daylight and site coverage. You also typically still need design work and an LBP. The exemption removes the consent paperwork and waiting time, not the cost of building well or the council charges.
2026 Granny Flat Build Cost Guide
| Build quality | Cost per m2 (approx) | What you typically get |
|---|
| Standard | $2,500 to $3,500 | Simple layout, standard fittings, kitset or volume builder |
| Mid-range | $3,500 to $4,500 | Better finishes, more glazing, some customisation |
| High specification | $4,500 to $6,000+ | Architectural design, premium materials, difficult sites |
These are construction costs only. Site conditions, location, access, the builder's workload and material prices all move the figure. A sloping or hard-to-access site, or one needing long service runs, pushes site preparation costs well above the typical range.
Why the Build Cost Is Only 75 to 80 Percent of the Total
It is easy to focus on the per-square-metre build price, but the build itself is usually only about 75 to 80 percent of the all-in cost. The remaining 20 to 25 percent comes from site works and services, design and project costs, and council development contributions. On the calculator's defaults, the $210,000 build cost is roughly 79 percent of the $263,000 all-in total. Budgeting only for the build is the most common way granny flat projects blow their budget.
What the Extra Costs Cover
- Site preparation and services connections: earthworks, foundations, a driveway or path, and connecting water, wastewater, stormwater and power. Commonly $20,000 to $40,000, and much more on a difficult site or where service upgrades are needed.
- Design and project costs: plans, a Licensed Building Practitioner, any engineering, and project management. Around $8,000 to $15,000 for a straightforward minor dwelling.
- Development contributions: a one-off charge councils levy on new dwellings to fund infrastructure. These still apply even when no consent is required. They vary widely by council and zone, commonly $10,000 to $25,000.
Worked Example
Take the calculator defaults: a 60m2 granny flat at a mid-range build rate of $3,500 per m2.
- Build cost: 60 × $3,500 = $210,000
- Site preparation and services: $30,000
- Design and project costs: $8,000
- Development contributions: $15,000
- All-in cost: $263,000
- All-in cost per m2: $263,000 ÷ 60 = $4,383 per m2
In this example the $210,000 build cost is about 80 percent of the $263,000 all-in figure, with the remaining 20 percent made up of site works, design and council contributions.
Frequently Asked Questions
How much does a granny flat cost to build in NZ?
As a rough 2026 guide, expect $2,500 to $3,500 per m2 for a standard build, $3,500 to $4,500 mid-range, and $4,500 to $6,000 or more for high specification. A typical 60m2 mid-range flat is around $210,000 in build cost, or roughly $260,000 to $290,000 all-in once site works, design and development contributions are added. The build cost is usually only 75 to 80 percent of the final figure.
Does consent-free building make a granny flat cheaper?
It saves consent and inspection fees and time, but not the cost of the build itself. You still pay development contributions, still must meet the Building Code, RMA and title obligations, and most owners still pay for design and a Licensed Building Practitioner. The exemption removes paperwork and waiting, not materials, labour, services and council charges.
What extra costs apply on top of the build price?
Site preparation and services connections (commonly $20,000 to $40,000), design and project costs ($8,000 to $15,000), and council development contributions ($10,000 to $25,000). Connecting a new dwelling to existing services on the same title can also trigger upgrade costs. Together these typically add 20 to 25 percent on top of the build price.
Related Calculators
Sources: MBIE / Building Performance, granny flats and the building consent exemption (building.govt.nz). New Zealand granny flat and minor dwelling cost guides, including Sonder Architecture and industry 2026 build cost data. Council development contributions policies (individual council websites).
This calculator provides indicative estimates only and is not building, planning, legal or financial advice. Actual costs depend on your site, design, builder, location, material prices and council charges. The consent-free exemption does not remove your Building Code, development contribution, title or Resource Management Act obligations. Always confirm requirements and quotes with your local council and a Licensed Building Practitioner before committing.
