Types of wall insulation
Bulk insulation comes as segments or blankets. Segments (also known as biscuits) are pre-cut to small standard pieces of insulation whereas blanket products are available in rolls. If you put bulk insulation into existing walls you’ll need to remove the wall lining or cladding.
Choosing a bulk insulation product
Bulk insulation can be made from various materials including polyester, wool, and fibreglass. Whatever material you opt for, a good wall insulation product should meet the following criteria:
- fit for purpose - it should be intended for installation in walls
- highest R-value possible for the thickness of your walls
- right width for the stud spacing in your walls
- compliant with the New Zealand Standard AS/NZS 4859.1 (look for the compliance statement on the insulation packaging).
You should also check the performance guarantees and instructions for safely handling and installing insulation offered by manufacturers on their products.
If you don't want to go to the trouble of removing wall linings or cladding, injected or loose-fill insulation is a good alternative. Injected insulation is pumped into existing walls through small holes in the cladding or lining.
Before putting in any type of insulation into existing walls, it’s important that you make sure the wall cladding is weather-tight and there is a good wall underlay behind the cladding. This is difficult to assess without opening the walls, so consult a registered surveyor before you consider injected insulation.
There have been some concerns raised about injected foam insulation and the potential for it to transfer water in brick veneer houses. This was flagged as a potential issue in a report available on the BRANZ website.
Performance of injected wall insulation
In New Zealand the most commonly used type of injected wall insulation is urea formaldehyde foam insulation (UFFI). This is injected as foam which then dries.
Research by BRANZ found that the actual R-value of UFFI insulation is about 50% lower in a house than if measured in a test lab. This is because the UFFI shrinks as it dries, and because it’s injected into existing walls, it isn’t possible to see whether the cavity has been fully filled.
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 UFFI will make a difference. Taking the wall linings off and installing bulk insulation gives you an R-value of about R1.8 - R2.4.