Installing underfloor insulation

Use a trained professional to install or upgrade your insulation, as even small installation faults can affect its performance, create safety hazards or shorten its life.

Using a qualified professional

Professional installers buy insulation in bulk so they may be able to supply and install your insulation for about the same as it would cost you to buy it in a hardware store. We recommend you get more than one quote so you can compare prices.

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

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DIY checklist

If you’re going to install underfloor insulation yourself, there are some things you should 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:

  • New Zealand Standard NZS 4246:2016 contains everything you need to know about installing insulation. It's easy to follow with lots of colour pictures, and it's free to download (see link below).
  • Safety - as with all DIY projects, there are safety considerations. Make sure you read and follow the Health and 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.
  • Existing insulation - a quick look under your house will tell you if you have any. If there is, you'll still want to check what state it's in (see link below).
  • Check 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).
  • If 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. If you can’t enclose your subfloor space, ensure you choose an insulation product that has been tested for performance and durability in windy conditions.

 New Zealand Standard for installing insulation

 Checking existing underfloor insulation

 Choosing underfloor insulation