Adding a second small dwelling to an existing property has become considerably more straightforward in New Zealand, but there is an important distinction between building consent exempt and build whatever you like.

Since 15 January 2026, certain new granny flats of up to 70 square metres can be built without a building consent. New national planning rules can also remove the need for resource consent where the property and proposed dwelling meet the relevant standards. For homeowners around Wellington, Porirua, the Hutt Valley and Kāpiti, that opens up useful options for extended family, independent living or simply making better use of an existing section.

The key is working out early whether your project actually fits the exemption.

The biggest change: some granny flats no longer need building consent

The new Building Act exemption applies to what the legislation calls a small stand-alone dwelling.

At its simplest, the dwelling must be completely new, standalone, single-storey and no more than 70m² in floor area. It still has to comply with the New Zealand Building Code, and the design and restricted building work must be completed or supervised by appropriately licensed building professionals.

That can remove a significant part of the traditional building-consent process, but it does not remove the need for good design, accurate documentation or competent construction.

For homeowners, that is the most important point to understand. The exemption is another pathway for building a small dwelling — it is not a lower standard of building.

Does your granny flat qualify for the exemption?

The 70m² limit gets most of the attention, but there are considerably more conditions behind it.

Under the current Building Performance granny-flat guidance, an exempt granny flat must meet requirements including:

• being wholly new rather than an extension or conversion of an existing building;

• being one storey with no mezzanine;

• a maximum building height of 4 metres above floor level;

• a floor level no more than 1 metre above the supporting ground;

• lightweight timber or steel framing;

• at least 2 metres separation from another residential building or legal boundary;

• lightweight roofing and compliant wall cladding;

• compliant water supply, sanitary plumbing, drainage and stormwater systems; and

• design and construction by the required licensed professionals.

There are some less obvious restrictions as well. For example, the exemption does not accommodate a level-entry or wet-floor shower requiring a waterproof membrane. That is worth knowing if the dwelling is being planned specifically for an older parent or someone with mobility requirements.

An existing garage or sleepout also cannot simply be converted under this particular exemption because the dwelling has to be wholly new. A garage conversion may still be perfectly achievable, but it follows a different building and consenting pathway.

That is where an early conversation about what you actually want from the space can save redesign later.

No building consent does not mean no process

Before building work starts under the exemption, the homeowner must obtain a Project Information Memorandum, or PIM, from the local council.

The application includes preliminary plans and a description of the proposed building work. The PIM supplies important site information such as planning requirements, known natural hazards and existing infrastructure.

The council's role under the exempt pathway is different from a normal building consent. It does not approve and inspect the granny flat throughout construction or issue a normal Code Compliance Certificate at the end. Responsibility for satisfying the exemption and Building Code requirements remains with the homeowner and the licensed professionals carrying out the work.

When the build is finished, the required final plans, Records of Work and relevant trade certificates must be provided to council. Development contributions can also apply.

So there is less consenting administration, but there is still a clear paper trail that needs to be managed properly.

Building consent and resource consent are separate questions

There are two sets of rules to consider.

The Building Act determines whether the actual building work qualifies for the 70m² building-consent exemption.

Separately, the National Environmental Standards for Detached Minor Residential Units, or NES-DMRU, provide a national planning pathway that can allow a granny flat without resource consent when its requirements are met. Those standards also came into force on 15 January 2026.

The planning rules cover matters such as the zone, the existing main dwelling, site coverage, separation from the principal dwelling and boundaries.

Local District Plan provisions have not disappeared either. In some situations a council's existing rule can be more permissive; in others, rules around hazards, earthworks, floor levels, stormwater or other site-specific matters can still apply.

This means under 70m² alone does not answer the consent question.

What do the rules mean around Wellington, Porirua and the Hutt?

The national framework is the same, but the site assessment still needs to be local.

Porirua City Council's granny-flat guidance confirms that the NES-DMRU applies across its relevant residential, rural, mixed-use and Māori-purpose zones. For the resource-consent exemption there must generally be a principal dwelling, only one granny flat under the national pathway, and relevant requirements around building coverage and separation need to be satisfied. Porirua also notes that other District Plan rules concerning hazards, earthworks and floor levels can still apply.

Lower Hutt provides similar guidance and specifically highlights matters such as permeable surfaces, stormwater detention, minimum floor levels, natural hazards and earthworks.

The practical lesson is not to select a generic 70m² plan first and try to force it onto the property afterwards. Check the property first, then design the dwelling around what the site allows.

Why Wellington sites still need an early site check

This is particularly important around the Wellington region.

Slope, access, wind exposure, retaining, drainage, existing services and identified natural hazards can have a major effect on how straightforward a small dwelling actually is to build.

A PIM can identify council-held information including flood or inundation risk, slippage, wind zone, stormwater and wastewater infrastructure and other site restrictions.

There is also the practical construction side. Getting a digger, concrete truck, building materials or prefabricated components down the side of an existing house can sometimes be more influential on the project than the size of the dwelling itself.

A good feasibility check should therefore look at the building, the land and how you are actually going to construct it.

Should you use the exemption or get a building consent?

The exempt pathway will suit plenty of projects, but it will not automatically be the best choice for every granny flat.

If the design needs to sit closer to a boundary, has a more complex structure, requires features outside the exemption conditions, or simply does not fit comfortably within the prescribed design limitations, the normal building-consent pathway may make more sense. The same applies where an extension or renovation would produce a better result than a standalone building.

It is better to choose the right process for the dwelling you want than compromise a good design simply to keep it inside an exemption.

The rules are continuing to develop. A Building Amendment Bill introduced in July 2026 proposes further changes to support off-site granny-flat construction, including allowing eligible off-site construction before a PIM is issued. As at 24 August 2026, those particular changes are proposed rather than current law, so anyone looking at an off-site option should check the current position before committing.

A practical way to get started

If you are considering a granny flat, start with the property rather than the floor plan.

Work out where the dwelling could realistically sit, check access and services, understand the relevant council and planning requirements, then bring the designer and builder into the conversation early.

Once the site and intended use are understood, you can decide whether the 70m² exemption is the right pathway or whether a consented design would produce a better result.

A little planning at that stage can prevent a lot of compromises once drawings, pricing and construction are already underway.

Frequently asked questions

Can I build a 70m² granny flat without building consent in Wellington?

Potentially. Since 15 January 2026, certain new, standalone, single-storey dwellings up to 70m² can use the building-consent exemption. All exemption conditions still have to be met, the building must comply with the Building Code, licensed professionals must be involved, and a PIM is required before applicable building work starts.

Do I still need resource consent for a granny flat?

Not necessarily. The NES-DMRU can allow a compliant detached minor residential unit without resource consent, but the site, zone and proposal must meet the applicable standards. Other planning or site-specific rules can still apply.

Can I convert my existing garage using the granny-flat exemption?

No. The 70m² granny-flat exemption applies to a wholly new standalone dwelling, not an alteration or conversion of an existing garage or sleepout. A garage conversion can still be possible but follows a different compliance pathway.

Does council inspect an exempt granny flat?

The normal building-consent inspection and CCC process does not apply to a granny flat built under the exemption. The homeowner and licensed professionals carry the responsibility for compliance, and specified documentation must be supplied to council.

Can anyone build the granny flat if it does not need consent?

No. The exemption requires the relevant design and construction work to be carried out or supervised by appropriately licensed building professionals.

Thinking about adding a granny flat?

If you are considering a granny flat or small standalone dwelling in Wellington, Porirua, Lower Hutt, Upper Hutt or Kāpiti, Newport Construction can help you look at the practical building side of the project before you commit to a design.

Get in touch with Harvey to discuss the property, what you want to achieve and the best place to start.