Underfloor insulation
If the floor is cold, you feel cold. Underfloor insulation is one of the first things to consider in most existing houses to make them warmer, healthier and more comfortable - and in homes with accessible underfloor spaces, it's relatively cheap and easy to do.
Before you start
Here are some things to look at before getting started on your underfloor insulation.
Are you eligible for funding? If your house was built before 2000, you are eligible for funding to get your insulation installed - find out more about Warm Up New Zealand: Heat Smart funding.
Check your 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 - find out how to check if your insulation is adequate.
Check that your underfoor is accessible. Your underfloor must be more than half a metre off the ground to be able to put in new insulation.
Consider using a qualified professional. This is the simplest way to get a good insulation solution, installed correctly and safely - find out more about using a qualified professional.
Check what repairs are needed. It's best to get your underfloor repairs sorted before your insulation is installed. Look for:
- borer and other pest infestations - find out more about these on the ConsumerBuild website.
- rotten piles or subfloor framing and any corroded fixings.
- electrical wiring issues.
- drainage, guttering, downpipe or plumbing problems (i.e. water flowing under your house after rain or from leaking pipes.
- obstructions (e.g. stored timber, rubbish).
- dampness (mould or mildew, or dirt that stains like mud when you rub it in your hand) - find out more about tackling dampness.
>> Learn more about underfloor repairs on the ConsumerBuild website.
Is your underfloor space open? Exposure to wind and weather can impact on your insulation's effectiveness and durability. Consider enclosing the sub-floor perimeter (ensuring 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 see what might work best for your house.
Building a new house or addition? It's much easier to get your insulation done properly at the outset than fix it up afterwards. There are some specific considerations - find out more about designing to keep in the heat.
How much 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.
Bulk insulation with a minimum R-value of R1.4 is recommended for existing homes in all areas of New Zealand.
Which insulation product?
There are two main types of underfloor insulation: bulk and foil insulation products. EECA recommends using bulk insulation as there are several safety and performance concerns with foil insulation - find out more about foil insulation.
Checklist for choosing a bulk insulation product
To get a suitable, effective bulk insulation product, choose one that is:
- Fit for purpose. It should be intended for installation under suspended floors.
- An R-value of at least R1.4. R-value is a measurement of the insulation's effectiveness - the higher the R-value the better.
- The right width. You need the correct width for your floor joist spacing (this can vary under older houses so you may need to measure between all joists).
- Compliant with the Standard AS/NZS 4859.1. Look for the AS/NZS 4859.1 Standard compliance statement on the insulation packaging.
- Installed hard against the underside of the floor. To be effective there should be no air gap between the bottom of the floor and the top of the insulation, so avoid products with ridges or similar.
- Able to perform in your location. If you live in a damp or windy location, you need a product that has been tested for performance and durability in such conditions - check with your supplier or the manufacturer.
You may also want to check:
- Performance guarantees offered by insulation manufacturers on their products
- The manufacturer's instructions for safely and correctly handling and installing the insulation, if you are thinking of doing it yourself.
>> Download a list of specific insulation products accepted for use under the Warm Up New Zealand: Heat Smart programme.
About bulk insulation
Bulk underfloor insulation can be made from polyester, wool, polystyrene, fibreglass and a range of other materials.
Bulk products have an R-value (a measurement of an insulation product's effectiveness), and are easier to install correctly than foil products.
In most cases bulk underfloor insulation products are friction fitted between the floor joists. This means that they are held in place by one edge being folded down to spring against the joist. Otherwise clips, or other fixings such as staples and strapping, are used. For more information, refer to the instructions supplied by the manufacturer.
Installing underfloor insulation
Correct installation is absolutely critical if underfloor insulation is to perform properly over its life.
Using a qualified professional
EECA recommends using a qualified professional, especially if you are unsure of how to access and safely work in an underfloor space. Look for an installer who:
- is competent with the New Zealand insulation installation standard NZS 4246; and
- has completed the insulation installer training of the Insulation Association of New Zealand (IAONZ) - see a list of graduates on the IAONZ website.
If your house was built before 2000, check out ENERGYWISE funding for underfloor and ceiling insulation - all installations under this programme are required to meet strict quality and safety requirements.
Doing it yourself
If you are considering the DIY approach, there is some good information available to help you install your insulation correctly and safely.
>> Find out more about installing insulation.
>> Learn about special safety considerations with underfloor electrics.
