Cavity Wall Insulation Options
Bulk Cavity Wall Insulation Options
Before putting in any type of cavity wall insulation into existing walls, it’s important to make sure the building has been assessed by an experienced professional and is suitable for cavity wall insulation.
Bulk cavity wall insulation comes as segments or blankets. Segments (batts) are pre-cut pieces of insulation whereas blanket products are available in rolls. To put bulk insulation into existing walls you’ll need to remove the wall lining or cladding which can be expensive and disruptive. When you remove the wall lining, do a thorough inspection of the wall for any leaks, presence and condition of any wall underlay (building paper) and electrical wiring. Bulk cavity wall insulation can be made from various materials including polyester, wool, and fibreglass. Most bulk options will require separation from the cladding or protection via building paper. Whatever bulk insulation you opt for, a good wall insulation product should meet the following criteria:
- intended for installation in walls
- correct thickness
- highest R-value possible for the thickness of your walls
- right width for the stud spacing in your walls
- incorporate protection from moisture ingress
Blown-in Cavity Wall Insulation Options
Injected or blown-in insulation is blown (pumped) into existing walls through small holes in the cladding or lining. It can be made from various materials such as urea formaldehyde foam, wool or fibreglass fibres or polystyrene beads. Some blown-in insulation products are approved for installation in walls without a wall underlay or for installation into a drained and ventilated wall cavity (like brick veneer). There are two different ways of installing blown-in cavity wall insulation into walls. From the inside, which keeps the exterior cladding and the wall underlay intact, but requires some redecoration. Or from the outside, which is much less disruptive.
Whatever blown-in cavity wall insulation option you go for, a good system should meet the following criteria:
- intended for installation in walls (with or without building paper)
- feature water repellency
- provide the highest R-value possible for the thickness of your walls
- be installed by training professionals
- incorporate a robust and proven repair method.
WARNING – Injected urea formaldehyde foam insulation (UFFI)
Urea formaldehyde foam insulation (UFFI) 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. 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, however it will not provide the same performance gains as bulk or blown-in insulation.