Underslab Insulation

Benefits of Under Slab Insulation

• Better temperature control across Australia's hot and cold climates
• Improved energy efficiency and lower heating and cooling costs
• Effective moisture barrier against rising damp from the soil
• Noise reduction through the floor
• High compressive strength to support structural loads (minimum 25 psi recommended)
• Easy to handle and cut to size on site
• Long-term R-value that holds for the life of the building
• Compliance support for NCC energy efficiency requirements

Types of Concrete Slabs

There are several types of concrete slab floors used in Australian homes and commercial buildings, including slab-on-ground construction, suspended slab, and precast slab. The type of slab determines the right insulation approach, product thickness, and R-value required.

In mild climates, an uninsulated slab may perform adequately if the rest of the home is well insulated. However, in regions with cold winters or hot summers — which covers most of Australia — insulating beneath the slab and along the edges is strongly recommended.

What Is the Best Insulation for Under a Concrete Slab?

The most widely used under slab insulation products in Australia are rigid foam boards — specifically extruded polystyrene (XPS) and expanded polystyrene (EPS). Both have a closed-cell structure that resists moisture and heat transfer, and both offer the compressive strength needed to handle the weight of wet concrete. For maximum R-value per millimetre of thickness, PIR/polyiso boards such as Kingspan Kooltherm are the premium choice.

When selecting a product, match the R-value to your climate zone. Colder regions like Victoria and Tasmania typically require R2.5 or above; milder climate zones may need R1.0–R2.0 under the NCC.

If in-slab heating or hydronic floor systems are being installed, under-slab and slab edge insulation is mandatory under the National Construction Code.

Maximise Energy Savings With Whole-Home Insulation

A well-insulated concrete slab improves energy efficiency and comfort — but for the best results, it should be part of a complete insulation system. Combining under slab insulation with ceiling insulation, wall insulation, and roof insulation will prevent heat loss and gain throughout the year, reducing energy bills for the life of the building.

Need help choosing? Contact our team for project-specific advice, or read our under slab insulation guide for detailed R-value recommendations and installation tips. Australia-wide delivery available.