Checking underfloor insulation

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

Watch: How to check your underfloor insulation | 2:33 min

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 okay for now, although well-fitted modern bulk underfloor insulation can be much more effective. 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

Checking for dampness

While you're under your floor, check for damp or musty smells under your house. Check for leaks from pipes or signs of water flowing under the house when it’s raining. Moisture evaporating from the ground under the floor can be the biggest source of dampness in your house, even if the soil appears dry. If you have an enclosed basement, install a ground moisture barrier (black polythene sheet) - this will simply stop the moisture from moving out of the ground, into the air and up through your floor. Also, uncover any vents that may have been blocked by paint, soil, plants or barriers to keep pests out.

 Find out more about tackling dampness

Professional insulation check

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 – this service is often free of charge. If you do need some insulation, 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).

 New Zealand Standard for installing insulation NZS 4246:2016

Insulation in rental homes

In rental homes, insulation must meet the Residential Tenancies (Smoke Alarms and Insulation) Regulations 2016.

Insulation regulations for rental homes - Tenancy Services website