Subfloor – no insulation


Insulation was not a requirement when the house was built; insulation was required but never installed; the insulation has fallen out; the insulation has been blown out by wind


  • install subfloor insulation. Select a product specifically designed for use under floors. Proprietary products include polystyrene friction-fitted between the joists, and segments such as polyester, glass wool or sheep’s wool that come with tabs for fixing, or are held in place by strapping

  • the subfloor space, framing timber and underside of the floor should all be dry when installing insulation

  • ensure the insulation is pressed firmly against the underside of the floor. There should be no gaps (and no air movement) between insulation and floor and between sections of insulation

  • exposed subfloors may require sheet material fixed under the insulation to hold it firmly in place

  • where polystyrene is used, to be conservative, keep it separated from any PVC electrical cables that run under the floor with ducting or tape around the cables

  • thermal insulation (where it is reasonably practical to install it) has been a legal requirement in privately-owned rental homes since 1 July 2019. The general rule for ground floor suspended floors requires insulation of at least R 1.3. 

  • retrofitting or repairing foil insulation under floors has been banned

  • while you are working under a house, it is a good idea to also put insulation around any hot water pipes that run under the floor. Insulating foam tubes with a slit along one side can be pressed over the piping.