Insulate double-brick walls

Last updated: 15 September 2022

Double-brick walls have two skins of brickwork held together by brick ties, with an air gap in between. This type of construction was commonly used in Victorian houses before World War II (pre-1940). To check if your home has a double brick construction, knock on the inside wall. If it sounds solid it is most likely double brick, whereas a hollow sound indicates a brick veneer wall.

Insulation tips for double-brick walls

Select the right insulation

The most effective option for insulating double-brick walls is to use a pump-in loose-fill wall insulation. This product is installed by drilling holes in the wall between the bricks and pumping the insulation into the existing wall cavity. When the work is completed, the holes are filled with mortar.

There are many types of loose-fill insulation on the market, including specially treated (hydrophobic) granulated rock wool and specially treated cellulose fibre, which fill the gap between the brickwork. You can also consider polyurethane foam, which expands after being pumped into the wall cavity.

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.

Gaining access to double-brick walls

In some houses it is possible to lift roof tiles and gain access to the top of the wall cavity. In this case, a hose is dropped down into the wall cavity and the wall filled from the bottom up. In houses with metal roofs, sheets of tin might need to be lifted to gain access to the wall cavity, but this is more costly.

If it's not possible to install insulation through the roof, the installer will drill holes through the mortar between bricks or remove a whole brick to fill the cavity. The holes are then filled with mortar and the bricks replaced.

Environmental credentials

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


Ensure the insulation has been waterproofed and is suitable for use in a wall cavity. It should be specially treated so that it won't wick water across the wall space. Ask for evidence of this from the installation company when obtaining a quote.

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 will not compromise the quality of the insulation installation. If you are 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 installer.

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.