Wall insulation

Once you've insulated your ceiling and underfloor, installing wall insulation is the next most effective step for reducing heat loss in your home. It's difficult to insulate walls in existing houses without taking the lining or cladding off, so take the opportunity to do it if you're renovating.

Before you start

Here are some things to look at before getting started on your wall insulation.

Consider using a qualified professional. This is the simplest way to get a good insulation solution, installed correctly and safely - find out more about using a qualified professional.

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

Ensure your wall cavities are dry. Leaks or moisture accumulation issues in wall cavities can be exacerbated by installing insulation, and can lead to timber decay and toxic mould growth. To make sure that the outside cladding and flashings are in good repair and not leaking, and that there are no hidden plumbing leaks, EECA recommends consulting a registered building surveyor.

Check the building paper in your walls. Building paper prevents insulation from coming into contact with the outer cladding - this reduces the risk of the insulation getting damp, which would reduce its effectiveness. A building surveyor can check if there's intact building paper in the wall - if there's not, you can retrofit it provided your wall is dry - refer to page 20 of the NZS4246:2006 insulation installation standard.

Get your electrical wiring checked. If you have existing electrical wiring inside your external walls an electrical safety inspection by a registered electrician is recommended to ensure the wiring is in safe condition and adequately rated so it does not overheat when surrounded by insulation. Rewiring and/or installation of circuit breakers may be required in some houses with unsafe wiring.

Building a new house or addition? It's much easier to get your insulation done properly at the outset than fix it up afterwards. There are some specific considerations - find out more about designing to keep in the heat.

How much insulation?

The R-value is a measurement of the 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 becomes squashed, reducing its effectiveness.

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 for doing this, such as lining the inside of your walls with polystyrene insulation and then covering with internal wall board. EECA recommends you consult with a qualified builder about what might work in your house.

Which product?

There are two main types of wall insulation: bulk insulation, which requires cladding or wall linings to be removed, and injected foam insulation, which doesn't but may not perform quite as well.

Choosing a bulk insulation product

Bulk insulation can be made from different materials, including polyester, wool, fibreglass and other materials. Whatever material you opt for, a good wall insulation product should meet the following criteria.

  • Fit for purpose. It should be intended for installation in walls.
  • The highest R-value possible for the thickness of your walls - see above.
  • The right width. You need the correct width for the stud spacing in your walls.
  • Compliant with The Standard AS/NZS 4859.1. Look for the AS/NZS 4859.1 Standard compliance statement on the insulation packaging.

You may also want to check:

  • Performance guarantees offered by insulation manufacturers on their products

  • The manufacturer's instructions for safely and correctly handling and installing the insulation, if you are thinking of doing it yourself.

About bulk insulation

Bulk insulation comes as segments or blankets. Segments, also known as biscuits, are pre-cut to small standard pieces of insulation whereas blanket products are available in rolls of insulation. Both require removal of either the wall lining or cladding when retrofitting into existing walls. However, it means you can easily inspect the existing wall for any problems and check the coverage and quality of insulation installation.

About injected foam insulation

Injecting insulation into walls offers a retrofit alternative if you don't want to go to the trouble of removing wall linings. In New Zealand the most commonly used type of injected wall insulation is urea formaldehyde foam insulation (UFFI), which is pumped into existing walls as a foam that then dries.

>> Learn more about injected insulation.

Installing wall insulation

Correct installation is absolutely critical if wall insulation is to perform properly over its life.

Using a qualified professional

EECA recommends using a qualified professional to install your wall insulation. Look for an installer who:

  • is competent with the New Zealand insulation installation standard NZS 4246; and

  • has completed the insulation installer training of the Insulation Association of New Zealand (IAONZ) - see a list of graduates on the IAONZ website.

Doing it yourself

If you are considering the DIY approach, there is some good information available to help you install your insulation correctly and safely.

>> Find out more about installing insulation.

From the Resource Centre

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