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The Parka Wrap study to retrofit wall insulation from the outside started with the intent of improving a typical Kainga Ora building (a Starblock), what I realized soon after starting was that there are just a few Starblocks remaining but there are hundreds of thousands of New Zealand homes with no insulation in the walls. So my focus changed towards improving wall structures, but with the crazy idea that occupants shouldn’t be required to move out.

So the challenges,

  1. keep the occupants in the building
  2. improve the building’s thermal performance without destroying their capacity to dry and to remain durable. (AKA ‘let’s not have another leaky homes episode’)
  3. do the research but actually have a real outcome that’s applied to a building and tested.
  4. Prove it: test it.
  5. Create a guidance document to show how to do this.

Well, I got through the first four and I’m going to describe those, the focus was on a weatherboard wall so the details and photos show this. The method could be applied to other wall types – steel frame, block walls, precast concrete but the design guidance document nailing down every possible option and junction will have to wait.

The numbers are easy, according to BRANZ research there are 830,000 homes with substandard insulation. I’m going to suggest the number is so much higher simply because we have 1.8 million homes that already exist, and no one’s pretending more than a handful built over the past few years are ok. Our homes are not easy to heat, they are not well insulated, and most are not ventilated except having a fan in the bathroom.

Along with these numbers, it’s estimated here are at least 720,000 homes that have no insulation in the walls.  And when you think about our housing stock of 1.8 million homes, more than half of them were built before there was a requirement for insulation so this ‘720,000’ number starts to makes sense. Homes built soon after 1978 when insulation around the whole house was mandatory may have insulation, but realistically they are likely to be performing very poorly – think 1980’s cheap materials!

We only build about 20,000 houses nationally per year, and some of them are required for population growth. This means we will have our older buildings for a long time yet, so let’s fix them.

External insulation is not new; however, it has been poorly understood in NZ. We’ve made some buildings leak using materials that should not have been used. The method I have used for this project is to overlay sensible materials on the existing wall. There’s a bunch of reasons for this. One of them is to avoid unnecessary waste, another is to avoid unnecessary disruption to the occupants, another is to use the existing cladding as a substrate for new layers outside. The new layers are readily available right now and can be seen in the photos here. They are the weathertight layer Solitex Adhero, with a Rockwool outside that layer (that sounds a bit weird), then a batten to create a cavity with new cladding attached.

These layers make up a robust weathertight assembly that not only prevents drafts through the walls but provides thermal improvement where insulation is now installed as a continuous blanket. I know it’s robust because I’ve tested it with water and ridiculous wind pressures in Shelby Wright’s test booth, then racked the wall at high speed across 250mm of travel multiple times before testing again with more stormy weather.


Next blog: I’ll describe the initial testing on an old weatherboard wall, the new layers and the performance gains.