Installing wall insulation

Wall insulation makes a big difference to the comfort and warmth of your home. If you are planning renovations, it's a great time to consider wall insulation.


Video - Overview of installing wall insulation.

Using a qualified professional

We recommend using a trained professional to install your underfloor insulation. Look for an installer who:

  • works to the New Zealand Standard for installing insulation (NZS 4246:2016)
  • has completed the insulation installer training of the Insulation Association of New Zealand (IAONZ). 

 New Zealand Standard for installing insulation

Installation checklist

Check local building consent requirements

Retrofitting wall insulation needs a building consent unless your local council has granted an exemption. Either way, it must comply with the Building Code. Find out about requirements through your local council.

Ensure your wall cavities are dry

Leaks or moisture issues in wall cavities can be worsened by installing insulation, leading to timber decay and toxic mould growth. To make sure that the outside cladding and flashings are in good condition, and there are no hidden plumbing leaks, consult a registered building surveyor.

Check the building paper in your walls

Building paper prevents insulation from coming into contact with the outer cladding of your house, reducing the risk of it getting damp and losing its effectiveness. Building surveyors can check whether the building paper in your walls is intact. If not you can retrofit it, provided your wall is dry - refer to the NZS 4246:2016 insulation installation standard.

Get your electrical wiring checked

If you have existing electrical wiring inside your external walls, we recommend a safety inspection by a registered electrician. They can check whether your wiring is in safe condition and adequately rated so it doesn’t overheat when surrounded by insulation. Rewiring and circuit breakers may be required if your house has unsafe wiring.

How much wall insulation?

R-value is a measurement of insulation's effectiveness - the higher the R-value, the more effective it is at preventing heat loss. Look for insulation that is as thick as your wall cavity, with the highest R-value possible. If the insulation is thicker, it will need to be squashed and will be less effective. 

For most wall insulation materials, the highest R-values available for 90-100mm thick wall cavities are in the range of R2.5 to R2.8. If you want to add more insulation than can be fitted into your wall cavities, there are options like lining the inside of your walls with polystyrene insulation and covering with internal wallboard.

We recommend that you consult a qualified builder about what is best for your house.