Changes to the granny flats building consent exemption

Certified composite structural building products can now be used for granny flats, among other changes to the building consent exemption.  

From 8 October 2026, changes to the granny flats building consent exemption will allow more building products to be used and make it easier to use existing water supply, wastewater and stormwater services. 

What's changing? 

Certified composite structural building products can be used 

Granny flats can be built using certified composite structural building products. This includes some Structural Insulated Panel (SIP) systems and solid timber building systems. 

The building product must be used: 

• within the scope and limitations of its registered product certificate (CodeMark) 
• in accordance with the manufacturer’s instructions, to ensure it complies with the Building Code. 

This change supports modern construction methods, including prefabricated and off-site manufactured homes, and gives people more options when designing and building a granny flat. 

Using existing water and drainage services 

You may be able to use existing water supply, wastewater and stormwater services for a granny flat, rather than installing new systems. 

Using existing council or utility connections 

If your property is already connected to a council or other utility provider, you may be able to use or modify those connections for a granny flat. 

The utility provider must agree that the existing connection is suitable. You do not need a building consent to make these changes, but you must get any approvals required by the utility provider. 

Using existing on-site water and drainage systems 

If your property uses on-site systems, such as rainwater, wastewater treatment or stormwater disposal systems, you may be able to continue using them or upgrade them for your granny flat. 

The systems must have enough capacity and comply with the New Zealand Building Code. 

Installing a new on-site system 

If council or other utility services are not available, or cannot support an additional connection, you may be able to install a new on-site system for the granny flat. 

Updated guidance and resources 

From 8 October 2026, updated granny flats guidance, quick guides and other supporting resources will be available on the Building Performance website. 

New foundations guidance available 

Guidance is now available to help homeowners and building professionals understand foundation options for granny flats built under the building consent exemption. 

The guidance provides practical information to support the design and construction of granny flats.