Checking underfloor insulation

Check your underfloor insulation to make sure it hasn't shifted over time, and that there aren't any gaps.

DIY checklist

If you can access your underfloor area, have a look for insulation. There are 3 things you might find:

  • Bare floorboards and no insulation - in which case you need to get some fitted.
  • Foil-based product - if it's held in with metal staples, don't touch it. There's an electrocution risk if the staples have pierced electrical wires and the whole lot might be live. When checking or removing existing foil insulation, always turn off the power supply to the house and follow the Electrical Code of Practice ECP 55 which provides guidance for managing electrical safety risks of foil insulation. Get an electrician to help you if you’re not sure.
    If your foil appears to be well fitted and in good condition, then it’s probably working well. However, if the foil is ripped, parts of the foil are missing or there are gaps allowing airflow into the spaces above the foil it needs to be replaced with bulk insulation. Retrofitting or repairing foil insulation in residential buildings is now banned under section 26 of the Building Act 2004.
  • Bulk insulation - includes rigid polystyrene sheets, or softer products like polyester, wool and fibreglass. Check to see that any bulk insulation is tightly fitted against the underside of the floorboards with no gaps or pieces missing. If any has slipped or fallen out, you should replace it. You may need some clips or other fittings to hold it in place.

Electrical Code of Practice ECP 55 - Energy Safety website

Current warnings and bans issued under the Building Act - Building Performance website


Video - How to check your underfloor insulation

Checking for dampness

While you're under your floor, check to see if you have excess moisture in the ground. If your soil isn't a dry dust, or you've got damp or musty smells under your floor or in your house, you may have a moisture problem. If you have an enclosed basement, it should be ventilated through gaps or vents in the enclosed perimeter walls. Uncover any vents that may have been blocked by paint, soil, plants or barriers to keep pests out.

It's important to fix any of these problems - if the ground is still damp, you can install a ground vapour barrier. This will simply stop the moisture from moving out of the ground, into the air and up through your floor. 


Getting a professional to check for you

If you can't check your own insulation, or aren't sure if you need any, get a professional to come and have a look for you. It's free and if you do need some insulation installed, they can tell you if you qualify for funding. Look for an 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).

Find a professional through the Insulation Association of New Zealand

 Warm Up New Zealand: Healthy Homes programme