Installing underfloor insulation

Correct installation is really important if you want your underfloor insulation to perform properly over its life.

Using a qualified professional

If you aren't getting your insulation done under the Warm Up New Zealand: Healthy Homes programme, we recommend using a trained professional installer who:

  • works to the New Zealand insulation installation Standard NZS 4246:2016
  • has completed the insulation installer training of the Insulation Association of New Zealand (IAONZ).

 New Zealand Standard for installing insulation

DIY checklist

If you’re going to install underfloor insulation yourself, there’s a lot to think about. It can be a difficult, dirty and time-consuming job, and the quality of the job has a big impact on how well the insulation works.

Before you start:

  • Read and follow safety advice - in Appendix B of New Zealand standard NZS 4246:2016. If you're not sure, get a professional to install the insulation for you.
  • Check your insulation - a quick look under your house will tell you if you have any. If there is, check what state it's in.
  • Check that your underfloor is accessible - it must be more than half a metre off the ground, otherwise you’ll have trouble getting under the joists and bearers that hold the floor up.
  • Check whether any underfloor repairs are needed - before your insulation is installed. Look for
    • borer and other pest infestations
    • rotten piles or subfloor framing and any corroded fixings
    • electrical wiring issues
    • drainage, guttering, downpipe or plumbing problems (like water flowing under your house after rain or from leaking pipes)
    • obstructions (stored timber, rubbish)
    • dampness (mould or mildew, or dirt that stains like mud when you rub it in your hand).
  • Check that your underfloor space is open - exposure to wind and weather can impact the effectiveness and durability of your insulation. Consider enclosing the sub-floor perimeter (as long as you have building code-compliant vents), or installing plywood or fibre-cement sheets to the underside of the floor once your insulation is in. It's worth consulting a qualified builder to find out what will work best for your house.

 Checking underfloor insulation

 Tackling dampness

How much underfloor insulation?

The R-value is a measurement of the insulation's effectiveness - the higher the R-value, the more effective it is at preventing heat loss through your floor.

We recommend you use bulk underfloor insulation with a minimum R-value of R1.4 for existing homes in all areas of New Zealand.