Home ceiling insulation

Last updated: 15 September 2022

Effective ceiling insulation is the best barrier against the summer heat and the winter cold, saving you up to 20% on your heating and cooling energy costs. Most Victorian homes already have some form of ceiling insulation but, if it has been in your roof for a while, it may not be performing as well as it could.

Safety first

Ensure that you read our insulation health and safety tips before considering installation or repair of insulation. Learn to minimise risk to yourself and your property.

Check your current insulation

Go up into your roof space to see how much insulation you have and what type of insulation it is. Some ceiling insulation can lose its effectiveness as it settles and compacts over time, so check whether it needs to be topped up or replaced altogether. If the height of your existing ceiling insulation is less than 50mm thick it should be topped up.

Select the right insulation

Read about the two main types of insulation – bulk insulation and reflective foil insulation.

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

Always consider the amount of space that is available within your wall, floor or ceiling when selecting the type of bulk insulation you want to use because an insulation product which is compressed will reduce its R value, e.g. a 150mm thick glasswool product will lose 25% of its R value if squeezed into a 90mm space and may push the plasterboard off the framing.

Select the right R value

The R value is 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 therefore money) savings. Different products with the same R value will provide similar insulation performance, regardless of thickness or the type of material.

For the Victorian climate the recommended minimum R value for bulk ceiling insulation is R3.5. In Victoria's alpine climates higher levels of insulation are required – aim for R5.0 to achieve greater comfort and energy savings in your renovated home. Use the table below to estimate the R value required for your ceiling.

Existing roof insulation Minimum recommended R value of top up to achieve total R value of 3.5 Recommended R value of top up to achieve total R value of 5.0
Blow-in insulation (This assumes an R Value of 0) R3.5 R5.0
Less than 50mm of insulation (This assumes an R Value of 0) R3.5 R5.0
50–100 mm of insulation (This assumes an R Value of 1.5) R2.0 R3.5

Installation tips

1. Acoustic performance or Sound Transmission Class (STC) rating

Most insulation products provide a certain level of sound reduction as well as thermal insulation, offering extra incentive to insulate your ceiling. 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.

2. Electrical wiring

Electrical wiring is often covered when insulation is installed. Seek advice from your electrician to ensure 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 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.