Insulate weatherboard walls

Last updated: 15 December 2021

Weatherboard walls contain a simple timber frame and external weatherboard cladding. They have a lot of room for energy efficiency improvements, as most weatherboard houses constructed prior to 1990 are likely to have uninsulated walls.

Insulation tips for weatherboard walls

Select the right insulation

If you're removing the internal lining of your walls, there's a range of insulation batts that may be suitable for your wall insulation, including polyester, glass wool, rock wool and natural wool. Check the product's R value: a measure of a material's resistance to heat flow (known as thermal resistance). The higher the R value, the greater the resistance to heat transfer, the greater the insulating effect and the greater the energy (and money) savings. The recommended R value for wall insulation is R2.5 in Victoria.

Ensure insulation batts are less than 90mm thick

This will ensure that they will fit snugly within the wall frame. Be careful not to compress the batts, as this will reduce their efficiency. The batts should never touch the weatherboards as this could cause condensation build-up over time.


Add layers

If you're replacing weatherboards, it's a good idea to wrap the building in a layer of builder's paper or house wrap. You might also consider adding a layer of reflective foil over the insulation to reduce condensation build-up.

Consider loose-fill insulation

If you are not planning on removing any wall lining, specially treated loose-fill insulation can be pumped into the wall cavity. This could be installed by either drilling holes into the plasterboard from the inside, or drilling holes in between the weatherboards from the outside.

In some cases, you can also lift tiles or sheets of roofing to install the insulation from above the wall cavity. Remember to check the health and safety tips for installing insulation.

Environmental credentials

Research the environmental credentials of your insulation product, and look for products with low toxin levels.

Acoustic performance or Sound Transmission Class (STC) rating

Most insulation products will provide a certain level of sound reduction as well as thermal insulation, offering extra incentive to insulate your walls. Good acoustic performance could be important if you have a problem with external noise. Heavier insulation products like rock wool tend to have the best sound reduction performance for a given width.

Electrical wiring

Electrical wiring is often covered when insulation is installed. Seek advice from your electrician to ensure the wiring is suitable to be covered. Ensure that any work the electrician does won't compromise the quality of the insulation installation. If you're using an installation company, it will usually arrange an electrician check and include the cost in the quoted price.

Questions to ask your builder

Installing insulation carries potential risks and requires expert knowledge. Poor installation of insulation will affect its performance and your potential cost savings so it's important to ask the right questions of your installers.

National Standards and Codes of Practice

Various Australian standards and national codes of practice cover the installation of ceiling insulation products. For more information visit the Insulation Council of Australia and New Zealand (ICANZ) website.