ARA - ParkaWrap
AOTEAROA HOME RETROFIT PILOT

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The Parka Wrap study to retrofit wall insulation from the outside started with a research project to improve a typical Kainga Ora building (a Starblock). I realized soon after starting 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 the focus changed towards improving wall structures, but with the crazy idea that occupants shouldn’t be required to move out.

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So the challenges were:

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1. keep the occupants in the building

2. improve the building’s thermal performance without destroying its 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.

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Well, I got through the first four and I’m going to describe those, the focus was on a weatherboard wall. 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.

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.

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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 existing cladding as a substrate for new layers outside. The new layers are readily available in the market and can be seen in the photos here. They are the weathertight layer Solitex Adhero, with a Rockwool outside that layer, then a batten to create a cavity with new cladding attached. The new uPVC windows from Starke are in the same position as normal, but now the insulation sits in-line so the performance jumps radically.

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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 Test Lab’s test booth, then racked the wall at high speed across 250mm of travel multiple times before testing again with more stormy weather.

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It's always down to the details, and the Parka Wrap Ltd team have developed three specific products to make it all the others stay together. In the photos you’ll see prototypes (now all in production and patents pending). They are, the depth-adjustable cavity closer at the base of the wall, the height-adjustable window support cam that allows us to place the window in the best spot in line with the insulation, and a ‘banana bracket’ which copes with depth, angle and position variability across inconsistencies in an existing wall.

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Now when someone asks for a ‘how-to’ on Parka Wrap I can say, we are working on loads of details, options and further guidance. The Ara Parka Wrap house is the first one to have been taken all the way through the process:

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• Investigate structure

• Model energy demand

• Materials selection always including Ventilation (balanced pressure)

• Design and detail

• Consent package

• Quantity survey

• Procurement (all the products on this website)

• Install and QA/ Audit

• Blower Door test

• Review energy model and update where required

• *Certify to Low Energy Building standard and Homestar 

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