Passive House Costs Explored
I’ve been following the JLC articles on super-insulated homes; one consistent thread seems to be the extraordinary labor hours required for all the details, especially air-sealing. The latest by Christian Corson (“An Affordable Passive House,” 5/12, 6/12) was no exception. Although I like the Passive House concept, some of the requirements seem to offer little payback in the U.S., where natural gas costs a fraction of its cost in Europe. In Michigan, I can install a high-efficiency gas forced-air system for the same cost as this house’s hvac system (that’s one expensive ERV system!), and I don’t see the savings from all the extra insulation.
Could the author compare this to a conventional project and comment on his profit margin? On the question of affordability, a breakdown of the $210,000 construction cost would be helpful. What’s included? Obviously not the land, and I don’t see a garage. Is the entire first floor a concrete slab? Are the kitchen and baths complete? Is there a well and septic? Is the lighting LED? What was the cost delta for the windows? (I find energy-efficient windows very expensive.) Also, what did the author use for entry doors?
Why not use foam board instead of OSB for a thermal break on the ceiling? Isn’t there a cheaper approach to insulating and sealing the ceiling? Finally, a small supplemental wood stove seems a natural for this house (instead of baseboard electric). Did the author consider that, or is a stove “verboten” in Passive House standards?
Chris Corson responds: Why are we doing this? For me, the driver is climate change. We are on the brink of catastrophic, irreversible changes that will result not only in the extinction of species but ultimately in the loss of trillions of dollars of civil infrastructure. Passive House is a quantifiable approach that can achieve a 90 percent reduction in the energy consumption of the built environment. Given the global context, building healthy, comfortable, efficient homes that reduce the carbon footprint of the building to near zero using local, sustainable materials makes perfect sense.
While natural gas may be cheap right now, it is not renewable, and it’s being harvested with environmentally destructive methods. True energy security will come from renewables. The sun supplies 86,000 terawatts annually. Global consumption in 2010 was just above 50,000 terawatts — and that accounts for every home, building, appliance, and automobile on the planet. We have a multibillion-dollar industry waiting to be born. China, one of the world’s largest solar-panel producers, has already figured this out.
As for your specific questions, the home was built for the same cost as a home built to code in this market; my margin was lower by choice. It was our intent to demonstrate that a Passive House could be built affordably using materials readily available to all builders in the U.S. This home is just one example of how it can be done — I and other builders continue to develop practical methods to streamline the processes.
Regarding labor hours, there was nothing extraordinary about this job. The house was turn-keyed in six months, by two carpenters and a laborer who worked standard 40-hour weeks with no overtime — hardly a time sink.
There’s no garage, but the budget includes the house, driveway, site work, septic, and well. It does not include the PV, as the article pointed out. The downstairs finished floor is sealed, clear-coated concrete. The house has a full Ikea kitchen and finished baths. The lighting is 100 percent compact fluorescent.
I used Intus triple-glazed windows and doors on this project. The cost delta versus, say, an Anderson A-series double-glazed unit is zero. The doors are more expensive, at around $1,400 to $1,800 a pop. The construction and performance of these products is superior to U.S.-made products in every way.
The OSB ceiling is an air barrier, not a thermal break, and no, there is not a more affordable way to achieve the same performance.
Biomass systems are not forbidden in Passive Houses; in fact, biomass boilers are found frequently in European Passive Houses and other high-performance buildings. The units must be airtight, however, and need makeup air, so common inexpensive wood stoves are not the best choice. In this house, peak heating load is about 6,000 Btu per hour (with 7,345 HDD and a design temp of -2°F). Since the smallest woodstoves on the market are rated around 30,000 Btu/hr, you’d get severe overheating. So we used an air-source heat pump to supply both heating and cooling, for an installed cost of $2,000.