Injected insulation
Injecting insulation into walls is an alternative if you don't want to go to the trouble of removing wall linings or cladding. There are some performance considerations to be aware of with this type of insulation.
How it works
In New Zealand the most commonly used type of injected wall insulation is urea formaldehyde foam insulation (UFFI). This is pumped into existing walls as a foam that then dries.
Performance
Recent research by BRANZ found that the actual R-value (the indication of how well a material insulates) of UFFI insulation installed in a wall is a lot lower than as measured in the test lab. On average, the R-value reduces by about 50% - which means it is still insulating your walls, but not to such a high degree.
This is because the product shrinks as it dries. Also, because it is injected into walls after they are constructed, it is not possible to see whether the cavity has been fully insulated. Structural elements within the wall cavity (dwangs, lintels, double studs, diagonal bracing etc) can prevent some cavities from being filled. You should talk to the installers and ask about the injection process, and how it will work with your house.
The BRANZ research found that a typical weatherboard wall with 100mm cavities and UFFI insulation installed has an R-value of about R1.6. An uninsulated weatherboard wall is about R0.5 so it will make a difference. Taking the wall linings off and installing bulk insulation would give you an R-value of about R1.8 - R2.4.
Your house must be weathertight
Before putting in any type of insulation into existing walls, it is important to make sure that the wall cladding is weathertight and that there is a good wall underlay behind the cladding. As this is difficult to assess without opening the walls, before considering injected foam insulation you should consult a registered building surveyor.
There have been some concerns raised about injected foam insulation and the potential for it to transfer water in brick veneer houses. This is flagged as a potential issue in a recent report available on the BRANZ website.
Thinking about injecting insulation into your walls?
If you can, insulate your ceiling and under your floor first. Insulating your walls as well will make a difference - here are a few things to consider if you do it.
Check building consent requirements with your local council. Consult a registered building surveyor to ensure your walls are dry, have intact building paper and are suitable for injected foam insulation - find a registered building surveyor.
Get your electrical wiring checked. An electrical safety inspection by a registered electrician is recommended to ensure the wiring inside your external walls is in safe condition and adequately rated so it does not overheat when surrounded by insulation. Rewiring and/or installation of circuit breakers may be required in some houses with unsafe wiring.
Check that the installation has been done properly. Following installation of the injected foam, check whether all wall cavities have been fully insulated using thermal imaging - there are a number of providers available across New Zealand which you can find by searching the internet for "thermal imaging New Zealand".
