Carefully keeping the surrounding Ponderosa Pines safe, which provide critical shading in the summer, we dug out a foundation stem wall and crawl space, a design that is critical to the foamless flooring insulation system. Not only does this minimize the concrete use but 20 percent of the cement was replaced with fly ash. The framing is very conventional: 2×4 studs with I-joists spanning the floor and roof. For air sealing we primarily used plywood and tape.
To do air sealing right you have to find religion about making sure that every place where two building elements come together is properly sealed, well before they’re covered. At the foundation, we applied a plywood “seat” for the I-joist to sit on and a similar detail happened at the wall-to-ceiling connection. Because the walls will be very well insulated, we used vapor open materials for air tightness so moisture does not build up in the wall over time. The air barrier is closer to the living space so water will not condense on it if it gets really cold outside. The ceiling and North wall were wrapped with Intello—a “smart” membrane that changes its vapor profile depending on the relative humidity.
Why is air tightness such a big deal? Passive House requires a leakage test of .60 ACH at 50 Pascals or less because leakage is a fundamental way a building loses energy, and allows mold-making, rot-inducing moisture into a wall. The building’s airtight layer is done so we can test it before we install windows, insulation, and all the other stuff that can cover a potential problem. We hit a respectable .45 ACH at 50 Pascals, or roughly the equivalent of 8 square inches of total opening in the entire envelope.
Related: How to Design a Passive House Off-grid and Without Foam
Next, it was time to make the insulation layer. The primary insulation material is Applegate cellulose, sandwiched with Roxul mineral wool batt on the inside and Drainboardon the exterior. We started withLarsen Trusses—basically a ladder like frame made from 2×3 supported by plywood scraps and wrapped in weed fabric to hold the insulation. The Larson Trusses were screwed to the exterior wall to make large bays, and a 2.3/8″ layer of drainboard was then attached to that. After not finding a competent contractor to insulate the bays with cellulose, I purchased a machine and got dirty, learning the ins and outs of properly filling a 24″ wall cavity so the insulation won’t settle over time. Overall, we installed 1100 25-lb bags of the stuff, which is just about an entire semi-load. The best part is the insulation is all recycled from nearby Denver and produced only 100 miles south. The mineral wool board, on the other hand, had to be specially made and shipped from a factory in Canada.
TheIntus windows come from Lithuania, in their own container. While less than ideal, the cost and performance are untouched by any American window manufacturer. They swing inwards and can be placed so the exterior frame can be over-insulated to reduce heat loss through the frame. The PVC windows also are the largest compromise by far from my unhealthy materials list because it is highly toxicto manufacture and very hard to recycle.
Another vital Passive House technology is the Heat Recovery Ventilator. This technology uses two fans: one to extract bad air, and one to provide fresh air. A heat exchanger keeps the energy in the building, and if hooked up to an earth tube the house can be naturally cooled in the summer. The unit I selected was the first in the US from a Czech Republic manufacture called Air Pohoda. It uses an a stingy 32 watts in regular mode (important for being off grid) and is over 90 percent effective at reclaiming waste heat.
In the meantime, the energy model seemed to go haywire when new climate data was entered. I find some interesting issues when I went sleuthing for what happened. Finishes such as siding, drywall, finish plumbing, and electrical all have to be installed—the punch list never seems to end. In the last installment of this series, I’ll discover if it’s possible to live in a house in Colorado in wintertime with no working heat, and after doing the Passive House Planning Package software modeling for myself I get a huge surprise. We do the final blower door test with fingers crossed, and I decide to submit to the Passive House Academy for the German certification and forgo the Passive House Institute US certification. Ironically, I was thefirst to report on the US-German split in 2011, and that news became a very personal journey.
Images via Andrew Michler