Underfloor insulation
Research indicates that over one million New Zealand homes have no, or inadequate, underfloor insulation. [1] Some floors in New Zealand homes have particularly high heat loss, such as ill-fitted tongue and groove planking.
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Types of product
There are two main types of underfloor insulation: foil and bulk insulation products.
Foil
In the past, the most common material used for underfloor insulation was a reflective foil, stapled along the floor joists. Reflective foils do not have an R value by themselves, but work in the following ways:
- They trap air between the floor and the foil which serves as insulation
- Escaping radiant heat is reflected back into the house.
The performance of underfloor foil is completely dependent on how well it is installed. Incorrect installation will significantly reduce effectiveness.
People who install the foil insulation face a serious risk of electrocution. This can happen if the foil or staples used to fix it come into contact with live electric wires under the house. As foil is metal-based, it conducts electricity.
Messy electric wiring is very common under New Zealand houses. It can be hard to see during foil installation due to inadequate light and the limited mobility of installers under the house.
EECA doesn’t recommend the use of underfloor foil and this product isn’t covered in EECA’s insulation retrofit programmes.This is because of the safety risks, challenging installation, dubious performance and possible lack of durability.
Bulk products
Bulk underfloor insulation includes products such as polystyrene, wool, polyester or fibreglass.
These products fit between the floor joists. They either go hard against the underside of the floor or have a small air gap between the bottom of the floor and the top of the product.
EECA requires that products used in its funded insulation programmes have no air gaps as these can reduce the performance of the insulation.
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.
Bulk products do have an R value, and are easier to install correctly than foil products. EECA recommends using bulk underfloor insulation with a minimum thermal ressitance of R1.4.
Dealing with dampness
Any moisture or dampness in the area underneath or around the edge of your floor has the potential to make your house damp and musty. It may also reduce the effectiveness of your underfloor insulation and make you house harder to heat.
If the area underneath your house is damp then you should get any drainage issues checked by a professional. Also consider installing an on-ground vapour barrier in enclosed underfloor areas. For more detail, see page 45 of the standard for installing insulation.
Download the New Zealand standard on installing insulation, NZS4246:2006
Although dehumidifiers help fix the symptoms of damp problems, better drainage and/or an on-ground vapour barrier will fix the cause of the problem.
Take action
Apply for an insulation grant
Grants are available for ceiling and underfloor insulation, regardless of your income, if your house was built before 2000. Find out more about home insulation funding.
Keep safe when installing underfloor foil
It’s essential that you keep staples well clear of any power cables when stapling underfloor thermal insulation.
Read the safe work practices 'Installing under floor thermal insulation – Electric shock hazard' on the Energy Safety website.
Read the installation standard
Standards New Zealand has published a standard on installing insulation. It covers a variety of products available and provides detailed instructions on how they should be installed.
Download the New Zealand standard on installing insulation, NZS4246:2006
Semi-rigid underfloor insulation products aren’t presently covered by the standard. Please refer to the manufacturer’s installation instructions.
Seek professional advice
- Consult a builder or visit a hardware shop that sells insulation products
- Use our suppliers and partners directory
- Get a professional report of your home’s insulation requirements with a Home Energy Rating.
More information
- Home heating and energy options for New Zealanders can be found on the Consumer website - Consumer online.
Insulation
- For comprehensive information on insulation, download the Department of Building and Housing booklet Your guide to smarter insulation.
- For a comprehensive discussion on choosing insulation products, see the Smarter Homes website.
Product certification
- For a background to how products are certified, go to the Consumer Build website.
Building code
- Check with the Department of Building and Housing website for changes to the Building code.
- Visit the Department of Building and Housing website for a copy of ‘The Building Code Compliance Document Clause H1 Energy.'
Building Resources
Independent and unbiased research, testing, consultancy and information resource for the building and construction industry is available at:
Notes
Clark, S.J., Jones, M. & Page, I.C. 2005. New Zealand 2005 House Condition Survey. Wellington: BRANZ
