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Expandable granny flats in New Zealand: what the rules require
An expandable granny flat is built and fitted out in a factory, travels folded and expands on your section. In New Zealand it can use the 70 m² granny flat exemption only if it meets every condition, and two of them weigh most on a unit built overseas: the frame, and the PIM, which must be issued before any building work starts, including work in the factory.
What is an expandable granny flat?
It is a steel-framed unit finished inside at the factory. It travels folded, 2.2 m wide, inside a shipping container. On your section, its side sections expand and the unit is set on foundations designed for that section; there are no loose panels to assemble.
Sellers often name these units by length, such as "20 ft" or "30 ft". Our Yard 37 is 5.9 × 6.3 m expanded, with 35.2 m² of floor area inside the walls and two bedrooms; two of them travel end to end in one 40 ft High Cube container. Our Yard 57 is 9.0 × 6.3 m expanded, with about 54.3 m² inside the walls, two bedrooms and a separate living room; it fills a container on its own.
An expandable granny flat is not a tiny house on wheels: MBIE treats those as mobile buildings, with different requirements. Nor is it a converted shipping container: it is built as a home, with a steel frame and insulated wall panels.
Can an expandable unit use the granny flat exemption?
The exemption does not depend on how the home is built. MBIE's granny flats exemption guidance covers off-site construction, prefabricated or modular, and says that every condition of the exemption and every licensing requirement still applies. The conditions that matter most for an expandable unit:
| Condition | What to check |
|---|---|
| New, stand-alone, single storey, no mezzanine | That the unit is detached from the house and has no loft or mezzanine |
| 70 m² of floor area or less, measured between the finished internal faces of the external walls | The internal dimensions once expanded, not the overall size |
| A frame of lightweight building products, steel or timber, or a certified composite structural building product | The frame's sections and how they are assembled: see the framing rule below |
| Roof cladding of 20 kg/m² or less; wall cladding of 220 kg/m² or less | The weight of the roof and wall panels |
| At least 2 m from any other residential building and any legal boundary | The position of the expanded unit on your section |
| Plumbing and drainage to set acceptable solutions, no more than 30 fixture units, no pumped systems within the dwelling | The factory plumbing layout and its connection points |
| An independent source of supply for electricity; electric or gas heaters only | The electrical design for your section |
| No level-entry shower that needs a waterproof membrane | The shower fitted at the factory |
If any condition is not met, the work is not exempt and needs a building consent. The full list of conditions is in our guide to the 2026 granny flat rules.
Two questions about our units are open with MBIE, asked on 23 October 2026: whether a home built overseas can use the exemption, and whether the bolted steel frame of our units counts as a lightweight steel frame. Until MBIE answers in writing, we take no deposit for a project that relies on the exemption. If you do not want to wait, your project can go through a building consent instead: your quote then shows the consent fees and the extra time.
The framing rule: lightweight steel or timber, or a certified composite product
The exemption requires a frame made of lightweight building products, steel or timber, or a home built with a certified composite structural building product. That second option was added on 8 October 2026 by the Building (Exempt Small Stand-alone Dwellings) Order 2026. A certified composite structural building product has a registered product certificate, includes steel, timber or a wood-based product, contributes to the structure of the building and is designed for use as a roof, floor or wall, or as part of one.
The Act does not define "lightweight". MBIE's guidance points to the NASH Standard Part 2:2019 for light steel framed buildings, and suggests a building consent for a project that uses heavier or more complex materials, such as structural steel.
Our units have a galvanised, powder-coated Q235 steel frame, bolted with stainless fixings, with 150 × 210 × 3.0 mm columns. Whether that counts as a lightweight steel frame is one of the two questions we have asked MBIE, and your designer assesses it for your project.
Built in a factory: why the PIM comes first
Under the Building Act as at 8 October 2026, no building work on an exempt granny flat may begin before the council has issued a PIM for its final site, and the Act's definition of building work includes the manufacture of a modular component. One PIM is enough: a home built in a factory and transported to its final site does not need a second one.
In April 2026 the Government announced that exempt granny flats would be able to be built off-site before the PIM, with a PIM still required before any on-site work (announcement of 28 April 2026). That change is in the Building Amendment Bill, which had its first reading on 2 July 2026 (MBIE). Until it becomes law, the current rule applies.
So we start production only after your PIM is issued. The council has 10 working days to issue it once your application is complete, and the PIM lapses if the work is not completed within two years, unless the council allows more time: production, shipping, clearance and the site works all have to fit within that period.
Energy (H1): roof and floor insulation
The acceptable solution H1/AS1, sixth edition, effective since 27 November 2025, has dropped its schedule method. Compliance is shown either by its calculation method, which sets minimum construction R-values of R2.6 for roofs, R1.0 for walls and R1.3 for floors other than slab-on-ground, or by modelling under H1/VM1. The fifth edition can be used to show compliance only until 26 November 2026.
Many imported units have thin roof panels and uninsulated floors: check both first. Our Australian specification, with a 50 mm roof panel and no floor insulation, does not meet these minimums. For New Zealand we are specifying a thicker insulated roof and an insulated floor of at least R1.3, with upgraded walls and glazing where the H1 calculation for your climate zone requires them. You see that specification and its price in writing before you order, and your designer confirms H1 compliance for your section.
Weathertightness (E2) for a steel-framed panel unit
The acceptable solution E2/AS1, fourth edition, published on 28 July 2025, is titled "External moisture provisions for timber-framed buildings up to 10 m in height". A steel-framed unit with insulated sandwich panels is outside that scope, so its designer shows compliance with clause E2 another way: through a verification method, or an alternative solution based on the manufacturer's details and evidence.
Under the exemption, the home must comply fully with the Building Code: no waiver or modification of the code is available. Ask early for the cladding, flashing and joint details, because your designer needs them for this part.
Wiring done overseas: the electrical inspection
WorkSafe's guidance for imported buildings says the importer must confirm, before the building is offered for sale or supply, that its electrical installation complies with AS/NZS 3000, the Wiring Rules. When the work was done overseas and there is no New Zealand certificate of compliance, the installation is checked under the assessment approach, and a record of assessment is issued instead. The importer also issues an installation supplier declaration of conformity, and provides documents showing that the fittings are safe, with extra requirements for declared medium-risk and high-risk articles.
Our units are wired at the factory to AS/NZS 3000, and a New Zealand electrical inspector assesses the installation before connection. As the importer, you sign the declaration for the installation: we prepare it with the test results, the declarations for each fitting and the wiring layout, and go through it with you. After connection, the licensed electrician named in your quote issues the certificate of compliance and the electrical safety certificate.
Asbestos and biosecurity at the border
Importing any product that contains asbestos is prohibited unless the EPA grants a permit, and the Imports and Exports (Asbestos-containing Products) Prohibition Order 2016 sets no minimum quantity. Ask for test reports from an accredited laboratory, not a declaration. Our materials are tested by an accredited laboratory, and you receive the reports.
At the border, the container goes to a transitional facility to be unpacked. It travels with a biosecurity declaration, and MPI checks it for signs of pests and for contaminants such as soil. Wooden pallets or crates must meet MPI's wood packaging requirements. Our page on the steps from factory to section shows the order of events.
If the exemption does not fit: building consent
An owner can always choose a building consent for a small stand-alone dwelling, even when it would qualify for the exemption. MBIE suggests that route if, among other cases, the land has a natural hazard that cannot be managed as the exemption requires, if you want to use heavier materials such as structural steel, or if you prefer the certainty of a formal approval for insurance, resale or future work. With a building consent, the council checks the design and inspects the work.
For our units, a building consent is also the alternative while MBIE's answer is pending, or if that answer rules out the exemption: your quote then shows the consent fees and the extra time.
Checklist before you order
- The frame: your designer's assessment and, for our units, MBIE's written answer or the building consent route.
- The floor area inside the walls once expanded, and the 2 m distances on your section.
- The New Zealand specification for H1, with the roof and floor R-values, in writing.
- Your PIM, issued before any production starts.
- The electrical documents: the record of assessment, the declaration for the installation and the documents for each fitting.
- Asbestos test reports from an accredited laboratory.
- The plumbing layout: fixture units, connection points, no pumps within the dwelling.
- Truck and crane access to your section, and a written quote with the GST and import charges. Our guide to granny flat costs in Auckland lists every line.
Frequently asked questions
Is an expandable granny flat a converted shipping container?
No. It travels folded inside a shipping container, but it is built as a home: our units have a steel frame, insulated wall panels, a bathroom and a kitchenette, finished at the factory.
Can the factory build my unit before the PIM?
Not under the Building Act as at 8 October 2026: no building work may begin before the PIM, and building work includes the manufacture of a modular component. The Building Amendment Bill would allow eligible off-site-built granny flats to be built before the PIM; until it is law, we start production only after your PIM is issued.
Where can I put an expandable granny flat?
On a section with a principal home, at least 2 m from the boundaries and from other homes, with truck and crane access. The national planning standard allows one detached minor residential unit per site: our guide to minor dwellings in Auckland explains how the planning rules apply there.
How much does an expandable granny flat cost in New Zealand?
Our units are turnkey from NZD 170,000 for a Yard 37 and from NZD 230,000 for a Yard 57, on a standard metro Auckland section, GST included. Elsewhere, delivery and site works are priced in your quote.
General information, based on official sources read on 26 October 2026. It does not replace advice from your designer, your council or a lawyer. Rules change: check the current version before you commit.