[Editor's note: This is the first part of a two-part story; it provides a background on Passive House, a project overview, and a description of the foundation and structural wall framing. Next month the story will continue with completion of the wall and roof framing, air-sealing, insulation, mechanicals, and finishes.]
I've been working in construction since I was a kid. I've worked on job sites in New York, Florida, California, Massachusetts, and Maine, where I now run my own company. Along the way, I've managed more than a few big expensive projects, but none of them was as satisfying as the work I'm doing now - designing and building affordable houses to the Passive House standard, arguably the most stringent energy-efficiency building spec in the world.
The big-picture goal of the Passive House movement is to nearly eliminate housing's share of climate change by slashing energy consumption to about 6 percent of that used in conventional homes (see "Meeting and Beating the Metrics."). But to have a practical effect, the standard can't just apply to high-end projects with big budgets; it has to be within reach of ordinary working people. That's why I jumped at the chance to build a 1,600-square-foot two-bedroom Passive House in Knox, Maine, for a young working couple with a $210,000 budget.
I've taken the nine-day Passive House training course, where I also learned to use the Passive House Planning Package (PHPP), an energy-modeling software that determines whether a house will comply with the standard. For my first Passive House, I wanted not only to hit the performance targets but to build affordably, using methods familiar to any capable builder and readily available materials and products.
Hitting the Goal
To achieve the Passive House goals, we had to superinsulate every assembly on all sides of the house - foundation, walls, roof. The 8-inch foundation sits on a foot-thick polystyrene insulated-form system. The walls are "hybrid" assemblies, with an inner 2x4 bearing wall and a foot-thick outer structure built with wood I-joists and insulated with dense-pack cellulose. The conventional vented-attic truss roof has a 2-foot raised heel to accommodate deep-blown cellulose.
We also had to eliminate thermal bridging where these building elements meet, which we did by extending the exterior insulation to cover the ends of framing at joints and intersections.
And, finally, we had to make sure that the entire building envelope was meticulously air-sealed .
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All of these steps made the house completely airtight, so we installed a high-performance energy-recovery ventilator. This unit provides fresh air with minimal heat loss (or summertime heat gain) and very low operating energy consumption (21 watts). It also mixes the house air, distributing solar gains around the living space and maintaining a consistent living environment.
We were able to take care of the house's heating and cooling needs with a small, 13,600-Btu/hr heat pump, bought from a local distributor for $1,500. For backup, we distributed about 15 feet of electric resistance baseboard around the rooms. The electric heat won't run unless the heat pump breaks down - but if it does, those 15 feet should keep the whole house comfortably warm even on the coldest nights.
