Net Zero Metrics
Long post! TLDR, we can hit net zero with our design. See our Net-Zero Energuide Report and CHBA Net-Zero Energy Design Summary.
With the advice of an excellent team, our strategy for net zero focuses on the envelope performance first. Most of our heat loss is in windows and walls; upping the insulation is essential. Through a combination of rigid and batt insulation (+ sprayfoam as needed), we’ll need to hit R18-22 for walls, R32 for exposed or cold floors and R60 in the roof. This means “furring out” or rebuilding walls to turn 2x4 framing into 2x6 throughout.
We are opting to add insulation to the interior vs exterior of walls. Having explored both options, we believe this to be a more cost-effective strategy (if space permits, which in our case it does).
We are able to leave the foundation as-is (R0) which was a big consideration, given the low ceiling heights @ 7’5”in the basement (i.e. not wanting to lose any of that height) and HUGE cost ($ and carbon) of tearing up the slab to get insulation underneath.
Windows will be triple glazed to hit USI 1.0 or less (U-value 0.17 or R-5.7). We thought we could get there with double glazed, but partly because of limited room for solar on the roof, we are opting to go triple.
Our contractor will need to ensure an airtight construction with no more than 1.5 air changes per hour (ACH) at 50Pa (currently the house measures 9.7 ACH).
By adding a heat pump and heat recovery ventilator, switching to electric HW, and spec’ing LED lighting and energystar appliances, it is possible to drive our energy use down from 185GJ/year to 41GJ/year. That’s a 78% improvement from existing, and around 50% better than a typical new build in BC.
Finally, our design includes rooftop solar ~30 panels in all, on a (new) south facing roof @ 22.65° slope. This array is expected to generate 41GJ of energy annually.
41GJ used and 41GJ generated from on-site renewable = net 0Gj. So exciting and a little surreal to see these numbers zero out on paper!
#netzero #netzerohome #renovation #greenbuilding #sustainability #energymodelling
