Floor insulation

Floor insulation  
Adding insulation to an existing beam and joist floor is much easier than trying to improve insulation for a slab floor.

How heat enters and escapes through floors

The way your floor will contain or allow heat through depends largely on what type of sub-floor you have. Floors with a high thermal mass like concrete slabs will hold and retain heat, releasing it long into the night, while stump and joist floors will lose heat very rapidly.

Up to 10%-20% of the heat in a home can be lost and gained through the floor as the temperature fluctuates through the day. Having your floor insulated will improve your thermal envelope, allowing you to better control the temperature inside your house.


Types of floor insulation

The type of floor insulation you're able to use will mostly depend on the type of floor you’re using. Some common types include:

  • Fibreglass / glass wool batts
  • Rock wool batts
  • Polyurethane foam
  • Polystyrene panels



Some floors simply rely on the layers of insulation provided by carpet and underlay, but if you have exposed floor boards or another type of bare flooring this may not be an option. Other slab-type floors often have thermal breaks inserted into the slab when it’s cast; these stop heat from escaping through the floor underneath the walls, ensuring that the heat that's stored in the floor is not simply escaping outside through the edges of the slab.

Heated floors are sometimes insulated underneath the heating elements to stop the heat from flowing out through the slab underneath, but care must be taken - especially with electric underfloor heating - to ensure that the insulation doesn't interfere with any electrics. Floors constructed from some structural materials that already provide good insulation (like autoclaved aerated concrete, or AAC) won’t need to accommodate additional insulation as this is already built into the material.

The key to having decent floor insulation is making sure it is sealed well. This can help boost the R-value of your home and help protect the thermal envelope.


When should floor insulation be installed?

As is the case with walls, the easiest time to install floor insulation is during construction of the house - and indeed it may be required to boost the overall R-value of your home to meet the applicable Building Code of Australia (BCA) requirements.

Certain types of insulation - like thermal breaks in a concrete slab - will need to be done during the construction of the house, and can't be done thereafter. In general, retrofitting insulation to a slab floor is a difficult proposition (if it's possible at all to do so effectively).

Retrofitting insulation in stump and joist floors is much easier than retrofitting a slab floor. In most stump and joist floors, insulation panels or batts are available which are designed to fit comfortably between the floor joists, making the task fairly uncomplicated. Polyurethane foam can also be used to insulate effectively under these types of floors.