Home floor insulation

Last updated: 15 September 2022

Safety first

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

Select the right insulation

There are two main types of insulation – bulk insulation and reflective foil insulation.

Extruded or expanded polystyrene insulation boards can be used in underfloor insulation. This type of insulation can also be combined with reflective foil to form a blanket that helps create an insulated barrier from the outside air.

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 R value for floor insulation is R2, with a minimum requirement of R1.

Installation tips

A snug fit

Insulation batts should be installed snugly in between the timber floor joists. The batts can be held in place with tape if needed, or a layer of reflective foil can be installed (shiny side down) to achieve a greater benefit.

Underfloor ducts for heating systems

If the insulation will cover underfloor ducts for heating systems, ensure that the performance of the ducts is not impeded by the installation of the insulation.

Floor insulation

Acoustic performance or Sound Transmission Class (STC) rating

Most insulation products will provide a certain level of sound reduction as well as thermal insulation. Good acoustic performance could be important if you have a problem with external noise, as sound can enter the home from unsealed underfloor spaces. Heavier insulation products like rock wool tend to have the best sound reduction performance for a given width.

The structural integrity of products

Some products offer better strength and rigidity, encouraging a snug fit between the timber floor joists. Consider using these products for your underfloor insulation.

Soft furnishings

Carpet and rugs can add an insulating barrier between you and the cool air under your house in winter.

Insulating a concrete slab

Thermal mass from a concrete slab can be effective in winter due to its ability to store heat during the day and release it later. Thermal mass stores heat, either from direct solar radiation or by absorbing heat from the air.

If you are creating a new concrete slab as part of your renovation, be sure to:

  • place your slab where it can receive northern sunlight. The slab will heat up during the day and release that heat slowly into your home in the evening
  • use polystyrene pods in your slab to improve its thermal performance
  • add slab edge insulation to stabilise the concrete from fluctuating air temperatures.

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 insulation products. For more information visit the Insulation Council of Australia and New Zealand (ICANZ) website.