ARA - ParkaWrap
AOTEAROA HOME RETROFIT PILOT
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.
So the challenges were:
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keep the occupants in the building
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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’)
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do the research but actually have a real outcome that’s applied to a building and tested.
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Prove it: test it.
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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. 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.
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.
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.
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.
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
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Model energy demand
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Materials selection always including Ventilation (balanced pressure)
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Design and detail
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Consent package
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Quantity survey
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Procurement (all the products on this website)
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Install and QA/ Audit
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Blower Door test
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Review energy model and update where required
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*Certify to Low Energy Building standard and Homestar
" The idea and the process that will start a revolution of renovation"
Frequently asked questions
Can you explain the stainless brackets?
Stainless brackets are the first prototype of a structural fixing that copes with different depths of insulation, and different angles of attachment due to the hinged arm. The next iteration of the product is both stronger and lower thermal conductivity due to material and improved design. The structural capacity is both vertical and horizontal due to the fixing to the external batten – two screw fixings locks the arm in place. Patent pending.
Is that a metal clip for the cavity batten? What effect did that have on the modelling?
The thermal conductivity of the banana clip through the insulation is expected to be less than the equivalent two screws when using other fixing systems. Thermal modelling not yet complete. Compared to other fixing systems this is a low-conductivity design.
The raptor clips were cost effective or just deemed easier to install consistently?
The Banana Clips allow for consistency of finish with wildly varying substrate (weatherboard, no weatherboard, varying angles). They use a self-sealing tape beneath the base plate to ensure weathertightness is maintained.
Are screws through insulation very long and structural?
Long screws through insulation is common practice in North America and rely on the density of the Rockwool to create a truss. Search RDH Canada ‘Long screws through insulation’. This is possible here and is how Jon tested the system however the Banana Clips are fixed on prior to insulation therefore the screw penetrations are sealed where they penetrate the weathertightness (ADHERO peel and stick).
What are those brackets holding the battens?
Banana Clips from Parka Wrap Ltd. They have other names, some of them rude.
Are the banana brackets designed to carry various loadings from various cladding types?
Yes, final engineering of the load capacity is underway. Like other systems, cladding gravity loads, wind loads, support rail capacity... all factor into how many clips are required.
Any thoughts on how you would accommodate vertical cladding?
We have used other systems for vertical cladding, Nuwall have an option for example.
Alternatively, an additional horizontal rail would be applied over the vertical battens. Similar to a good roof design.
Do those banana brackets have any insulation breaks? Are they metal?
At this stage we have not included additional thermal breaks but if required for particular performance it’s certainly possible. Considering the bridge itself fixes onto a low-conductive material (weatherboards) in this instance, there was no need for additional thermal break.
Since the existing cladding is still in place, strictly speaking does overlaying the building with a new cladding (and insulation) require a Building Consent?
Good question. At this stage I’m treating our changes as consent triggers. At some future point I hope to see a formal consent exemption process within limitations such as Christchurch City Council’s. It will not be Codemark though, far too many elements at play on too many variations.
What barriers are there to council acceptance of the system, if we were to use this on a current project?
Firstly it’s an alternative solution and needs to be described. Using the cladding system’s compliance pathway will resolve some of this, and the VM2 tested window sealing connection from pro clima (TESCON EXTORA Profil) has been installed in this project. The compliance pathway includes an explanation of:
B1 Structure (both for existing structural integrity/capacity and for the added elements to connect new cladding).
B2 Durability – normal statements.
E2 rainscreen design includes drainage channel and complete water-resistant layer installed outside the original cladding.
E3 – Internal Moisture – the insulated system including uPVC window frames creates internal surfaces with higher temperatures than is normal ‘everywhere’, combined with a ventilation system to remove high humidity.
G4 Ventilation – whole house ventilation using balance-pressure with heat-recovery. G6 Acoustics (not quantified in useful terms yet).
H1 Energy Efficiency – well quantified through the energy modelling that can be incorporated into the process to avoid using Schedule Method, instead the H1/VM1 pathway can be used.
What were the total costs, including the design costs?
Yet to be completed. Looking at around $150,000 for this project, which we compare to $300,000+ for removing tenants, renovation, replacing tenants (current social housing model).
Did you take any sound level measurements pre-parka?
No, the house had no windows when we started the project, the good news is there are near identical homes sitting either side and we will have decibel meters to compare.
