13 - A mid-stream upgrade!

Although the house was already nicely insulated I was inspired by some articles in the Carters builders magazine about New Zealand's first certified Passive House (http://passivehouse1nz.blogspot.co.nz/) and the technology & design which allow it to balance the heating gains and losses so well that it needs less than 15 kWh of heating per square metre per year to maintain an average temperature of 21 degrees celsius! (see also the Passive House Institute of NZ - http://phinz.org.nz/)

I found out via the German Passive House Institute that there were two certified architects in Christchurch so I met with one to review my plans and see what could be done to improve the thermal design even further, allowing for the fact that we were already underway and the slab and foundations had been poured.

He suggested that I:
  • Add a 50mm layer of eXtruded polystyrene (XPS) on the outside of the foundation face to stop the thermal bridging from the outside air to the floor slab edge (and cement plaster the surface for durability).
  • Add an air barrier membrane to vastly improve the real-world performance of the insulation by removing the usual direct air transfer of heat through the joints between the insulation and the surrounding woodwork.
  • Add a second skin internal wall which would act as a services cavity for the electric wiring, water piping and network and stereo cabling, etc. This would allow the external wall insulation to have less interruptions and the horizontal services cavity battens would greatly reduce the thermal bridging effect caused by the studs.
  • Because the services cavity battens would mean that the Gib is no longer direct-fixed on the external walls, add a layer of external plywood for even better building bracing.
  • Add a 50mm external drainage cavity to allow the Shadowclad exterior to drain down the outside face of the XPS insulation.
  • Increase the window specification to be at least thermally-broken double-glazing or better yet, thermally-broken triple-glazing in wooden or PVC frames.
  • Add in a passive house certified mechanical heat recovery ventilation system which is at least 92-95% efficient at recovering the outgoing heat to the incoming air. This would remove all condensation build up and allow the heating systems to work more effectively.

I have re-drawn the plans to incorporate these changes and submitted a Building Consent Amendment Application to Waimakariri District Council..... Now we wait a minimum of 20 working days to know if we can proceed!

In the mean time (in advance of approval) I have completely clad the exterior walls with Plywood bracing and covered over the South-facing windows to stop the winter rain from wetting the house framing. It is a little bit of a gamble but I reason that there is no chance they will refuse an increase in the bracing of the building and doing so now protects the structural elements of the building from damage. We are stopping at that point to allow the inspectors to be able to see that we have nailed everything off according to the CCH bracing specifications.

Here is a mock up drawing of all the elements....

....and a model built for the window company to allow calculating the depth of the window sills.

XPS insulation in the external wall junctions that won't be accessible once the bracing and cladding are on....

The first bracing sheet being positioned.

Victor liked building on our site so much he came back for another week - Thanks Victor!

...loving the handy cordless skill saw!

Jonathan & Amelie test their precision hole cutting skills!

See you CAN sit down on the job and still get things done!

Strong and tucked up from the winter weather....

Temporarily covered over the window openings on the South side to keep out the rain

....and now we wait for the Council to review our changes before we can do anything more...

Next Page....  14 - warm toes