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

Find a professional through the Insulation Association of New Zealand

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.