Wall insulation

If you have insulated the ceiling and underfloor your house will be warmer, but in most houses the largest proportion of heat will now be lost through the uninsulated walls. Wall insulation will help slow the heat lost this way.

Take action

It’s difficult to insulate walls in existing houses without taking the lining or cladding off. Take the opportunity to insulate when you renovate, and have either the lining on the inside or the outside cladding of external walls removed.

Make sure the outside cladding is in good repair and not leaking, and that there is building paper in the wall. Insulation should not come into contact with outer cladding. This reduces the risk of the insulation getting damp, which would reduce its effectiveness.

How much wall insulation?

The New Zealand Building Code specifies minimum mandatory insulation standards for new houses. Refer to the section Designing a new home.

Wall insulation should be as thick as the wall cavity without having to squash the insulation to fit it in. Squashing the insulation reduces its effectiveness.

Choose an insulation product with an R-value as high as possible for the thickness of your wall cavity. The R-value is a measurement of insulation's effectiveness - the higher the R-value the better.

You may want to add more insulation than can be fitted into your wall cavities. If this is the case, consider lining the inside of your walls with polystyrene insulation and then covering with internal wall board.

Installing wall insulation

Correct installation is critical if wall insulation is to perform properly over its life. Refer to page 30 of the NZ insulation Standard for more details on installing wall insulation.

Download the New Zealand standard on installing insulation, NZS4246:2006

What type of insulation?

Wall insulation can be made from polyester, wool, fibreglass and a range of other materials. Not all insulation is created equal though, and some products do have definite drawbacks.

If you are comparing different types of insulation, remember to check:

  • The performance guarantees that the insulation manufacturers offer on their products
  • That the insulation you are looking complies with the AS/NZS 4859.1 Standard. Look for an AS/NZS 4859.1 compliance statement on the insulation packaging
  • The installation instructions for safely installing the insulation, if you are thinking of doing it yourself.

Once you know these things, make sure you are comparing products with similar R-values.

Injected insulation

A type of insulation, called urea formaldehyde foam insulation (UFFI), is injected into the walls of your home. Having insulation injected into your walls without having to remove either the internal or external linings seems like a good option for many people, however EECA does not recommend this type of insulation.

There has been no credible research or testing on a number of potential issues with injected insulation:

  • The R-value, the measurement of insulation’s effectiveness, is hard to determine with this product. This is because it’s impossible to tell if a wall has been fully insulated. Also, the product shrinks slightly as it dries.
  • It’s unknown what the residual moisture levels are in walls after insulation.
  • The impact on wall constructions that are designed to be ventilated is unclear.
  • What levels of formaldehyde enter indoor areas as the insulation dries is unknown.
  • There is potential for damage to elements of the house, such as cracks in internal wall lining, loosened tiling, moisture damage to wall surfaces, blistering of paint surfaces, product escaping wall cavities, and adherence of product to surfaces.

More information

Insulation

For comprehensive information on insulation, download the Department of Building and Housing booklet Your guide to smarter insulation.

For a comprehensive discussion on choosing insulation products, see the Smarter Homes website.

Product certification

For a background to how products are certified, go to the Consumer Build website.

Building code

From the Resource Centre

Related documents and additional information: