Granny Flat Rules Updated
Changes to New Zealand’s granny-flat building-consent exemption took effect on 8 October 2026, clarifying how qualifying homes can use existing water, wastewater and stormwater infrastructure. The changes also expanded the permitted use of certain certified structural building products.[1]
MBIE announced the amendments on 10 September 2026. They came into effect on 8 October, building on the original January 2026 exemption.
For homeowners, the servicing changes make an assessment of the property’s existing infrastructure an important starting point.
The practical question is whether suitable services are already present—and what evidence or work is needed to accommodate another household. Existing utility connections can be used or altered for a qualifying granny flat where the provider accepts the arrangement. Qualifying alterations do not need building consent, but the provider’s required permissions still apply.[2] Before commissioning a separate connection, ask: Can the existing service accommodate the proposed dwelling, and will the provider accept that arrangement? Have the project team confirm the answer with the provider. This is the stage to establish the connection route, the work included in the proposal and who will complete it. Suitable existing on-site water, wastewater and stormwater systems may be used or upgraded. Capacity, Building Code compliance and any applicable resource-consent conditions remain relevant.[2] For wastewater, the assessment should look beyond the tank. MBIE identifies treatment capacity and the receiving land as parts of a functioning on-site system.[3] Our recommendation is to obtain that assessment before settling the new home’s location. Ask for the treatment equipment and land-application area to be shown together on the site plan.Start by assessing the existing connections
Existing on-site systems deserve a complete assessment
What this means for a project: establish which arrangement is being proposed—an existing connection, an existing on-site system, an upgrade or a new installation—then compare options on that basis.
New on-site systems remain an option where appropriate
Where network services are unavailable, including confirmed insufficient network capacity, a qualifying new on-site system may be used. A materially altered existing system is treated as new for the exemption. Applicable design requirements and other approvals still matter.[2]
Ask the designer to explain the scope of the proposed work and the evidence needed for it. That creates a clearer brief for equipment selection and installation.
More choice for some prefabricated construction systems
The October changes also permit eligible certified composite structural products, including some structural insulated panel and solid-timber systems.[1][2]
Registered product certificates have defined scopes and limitations. Ask the building supplier to demonstrate that the proposed use is covered, rather than treating certification as approval of the entire project.[4]
Include the foundations and services in that discussion, not just the wall and roof system.
What this means for composting toilets and greywater
For WCTNZ®, the update reinforces the value of assessing the complete property before selecting equipment.
A project may be able to use existing services, need an upgrade or require a new on-site arrangement. Waterless sanitation and greywater options should be considered within that wider design.
Our existing granny-flat guide explains the distinction: a required network connection does not automatically prevent a separate, compliant waterless toilet or supplementary greywater system. Equally, selecting those technologies does not remove a connection obligation or approve a proposed discharge arrangement.[5]
The opportunity is to select systems deliberately—matching the home, the property and the intended use—rather than assuming every additional dwelling needs the same package.
Review the servicing plan before ordering
Ask the project team to identify the existing infrastructure, confirm its suitability and explain what additional work is included in the proposal.
That conversation should cover both the building’s connections and the systems that receive its wastewater.
Read the complete 70 m² Granny Flat Rules, Myths and Wastewater Options guide for the wider exemption conditions and WCTNZ®’s sanitation guidance.
Plan the home and its services together
Share your proposed location, occupancy, floor plan and available services with WCTNZ®. We can help with product selection and the information your project team needs.
Discuss your project with WCTNZ®
