The decision to use building foils can be confusing as sometimes, it may be not allowed, or non-compliant, or just not suitable. This is not to say you should not use foils or that they can't be used effectively in certain situations. It just means you need to make sure you use them appropriately.
Foils not allowed
A ban (MBIE Ban 2016/001) on retrofitting or repairing foil insulation in residential properties came into force on 1 July last year, to reduce the electrical risks associated with installing foil.
The Ban applies to the following building methods:
- the installation of foil insulation into residential buildings with an existing electrical installation (retrofitting foil insulation)
- the repair of foil insulation in residential buildings with an existing electrical installation (such as stapling ripped or damaged foil back onto the floor joists of a building).
Although they refer to foil insulation, it is a metallic foil (usually aluminium) laminated to a core often of kraft paper and sometimes with a fibre reinforcing, and can be used anywhere in the building, normally as insulation (sometimes a vapour barrier).
This Ban has teeth, offences under this ban are likely to breach G9 of the Building Act, and are liable on conviction to fines up to $200,000.
MBIE recommend, if there are any concerns when removing old foil, that a licensed electrical worker check the installation is not live first. Either way, turning the power off while the removal is carried out would be prudent and reduce risk.
The Ban excludes:
- residential new builds
- non-residential buildings (commercial, industrial, etc)
- foil attached to rigid material (however, includes foils attached to non-rigid materials like insulation blanket)
- existing residential buildings with no existing electrical installation (eg. garden shed)
Foils not compliant
Amendment 3 (In force since 1 June 2017) to NZBC H1 brought in the new clause NZBC H1/AS1, 1.0.2, that, for the purpose of energy efficiency, specifically excludes the use of foil insulation from being an Acceptable Solution (under H1/AS1). So you can't include it in your insulation calculations, but subject to the other issues in this article, it does not preclude the use of foil for other purposes.
Foils not suitable
Foils in some situations, and sometimes disputably, may not be suitable:
- in areas with installed electrical cables due to the risk of fixings penetrating an electrical cable and the foil becoming live (see above)
- under sheet or T&G floors on top of joists, as it may increases the risk of squeaking
- as vapour barriers (by some experts) - this is not so much about the foil more the principles of vapour barriers, or rather the industry arguments for and against (these are ongoing)
- as reflective insulation - requires very careful detailing and installation to get the best performance (otherwise performance could be substandard) - further complicated by the vapour
- barrier issue - in some situations like underfloor, performance has been shown to reduce over time due to dust/corrosion and air movement.
Considerations when using foils
The decision to use building foils can be complex, but it does not mean that they don't have their place or can't be used effectively under the right circumstances, it just means you have to think carefully about it.
Depending on your project, consider such things as:
- what purpose you want to use foils for
- insulation or vapour barrier or both
- will it be effective
- is it allowed
- does it comply
- climate zone (climate makes a difference to use, cold climate versus tropics)
- type of project (frequently used successfully in open industrial & commercial type situations)
- where you want to use it
- is it in the right place as insulation
- is it in the right place for a vapour barrier
- will it trap moisture
- will it cause condensation issues
- is it safe
- is there a risk the floor will squeak
- are fire properties required
- how you use it
- is the detail effective (as insulation and/or vapour barrier)
- detailing types of construction (steel avoid condensation issues, timber avoid trapped moisture issues)
- can it be made air tight
- how does it work in conjunction with other forms of insulation
Masterspec
Related Masterspec sections offer some guidance on the use of foils, however it is the decisions at the design stages that are the most critical and effective. If in doubt consult with the foil manufacturer/supplier as to the best approach to suit your project.
LINKS
MBIE Ban on foil insulation
https://www.building.govt.nz/about-building-performance/news-and-updates/all-news-and-updates/bc-update-188/
EECA Choosing underfloor insulation
https://www.energywise.govt.nz/at-home/insulation/underfloor-insulation/choosing-underfloor-insulation/
NZBC H1 Energy Efficiency
https://www.building.govt.nz/assets/Uploads/building-code-compliance/h1-energy-efficiency/asvm/h1-energy-efficiency-4th-edition-amendment3.pdf
BRANZ Underfloor Reflective Foil (pre-dates Ban but has some useful information)
http://www.buildmagazine.org.nz/assets/PDF/B104-20-ReflectiveFoil.pdf