Our building site was relatively quiet last week. Concrete is curing, and our electrician set up the main panel and meter in anticipation of CVPS turning on the electricity this week. Ted and I also spoke with several solar installers to see about getting some PV panels at the roof ridge and also a solar hot water system. More on that as it unfolds.
The biggest news is that we recently partnered with Efficiency Vermont to pursue Passivhaus certification [follow the link to read their "About Us" page]. The cool part is that our house will be part of a research project to evaluate the suitability of Passivhaus construction for Vermont. They'll install monitoring equipment in our house and closely study its performance.
Peter Schneider, Efficiency Vermont's Passivhaus consultant, was particularly interested in studying our house because it has several unusual features: a pier foundation and partial shading. Vermont's abundance of sloping, ledgy lots makes pier foundation a tempting solution, and of course trees are rampant hereabouts. So hopefully we'll provide useful data for would-be Passivhausers in North America.
Peter was on vacation last week, so he hasn't gotten farther than the first few rounds of PHPP tweaking, but Marc helped pick up the slack. This will all probably change this week, and I'm probably jinxing things just by typing this, but so far it looks like we can pull off Passivhaus performance with the following general specs:
- 11-7/8″ I-joist floor deck (16 oc), stuffed with dense-pack cellulose and with 4″ of polyiso underneath.
- 9.5″ I-joist wall framing (24 oc) filled with dense-pack cellulose and with 4″ of exterior polyiso.
- 24" roof joists, filled with dense-pack cellulose.
- Schuco SI-82+ windows, which we ordered this week from European Architectural Supply in Lincoln, MA. The windows are PH-certified and made from uPVC. Yes yes, PVC is evil, but this is unplasticized PVC which is apparently a bit less evil. It's made without phthalates and can be recycled, at least in Europe. But hopefully the windows won't need recycling for a long long time.
- Climatop Max and Climatop Ultra-N glass. The glass offered by Schuco is pretty darn impressive. For the south windows we upgraded to Climatop Max, which has a SHGC of 0.6, but for the rest of the house we went with the Climatop Ultra-N, which has an SHGC of 0.5. All the glass has a Ug of 0.105 (which PHPP callously rounds up to 0.11).
- We haven't decided for sure on the HRV yet, but we'll probably either do the Zehnder ComfoAir 350 or the Paul by Zehnder Novus 300. The latter adds about $1,400 to the already formidable cost, but the efficiency is 93% as opposed to the ComfoAir's 84%, which would win us quite a bit within PHPP. Another knob to turn would be to add more polyiso under the floor or use larger I-joists — we'll hopefully do the cost-benefit analysis this week and reach a verdict.
It seems like the biggest advantage in our design is the ludicrously simple house shape. We're basically building a shoebox with a shed roof, which means there aren't many corners or thermal bridges undermining our envelope. Marc, Ben, and Eli already minimized thermal bridging before we decided to go for Passivhaus certification, so we're picking up a lot of PHPP points without having to change our plans.
We're waiting on a few more details, though, including some THERM data Peter is confirming with PHIUS. Hopefully that won't kick us back out of the ballpark, but as I said we still have some knobs left to turn.