Inside the World's Tightest House
Tom Marsik and Kristin Donaldson of Dillingham, Alaska, recently achieved the distinction of building the world's tightest residential building. The World Record Academy, an international organization that certifies world records, presented the award to their home for achieving a blower door test of 0.05 ACH50. The house has a heat recovery ventilator (HRV) that controls fresh air and humidity to this nearly airtight dwelling.
Dillingham is a small municipality of around 2,400 residents about 335 miles southwest of Anchorage. The University of Alaska Fairbanks operates one of its several rural college extensions there, the Bristol Bay Campus. Tom Marsik is an assistant professor of sustainable energy at UAF BBC.
The Marsik-Donaldson house is comparatively small when compared to an average house in the United States. It has a 24-foot x 24-foot footprint, two bedrooms, one bathroom, and a total of 590 square feet of interior space. The usable floor area is small because the upstairs is a loft and not a full-floor second story.
The walls and ceiling are insulated with cellulose and a small layer of fiberglass batting. The walls are 28 inches thick with an approximate R-value of 90. The cathedral ceiling is rated about R-140. The floor is on grade and has R-35 of polystyrene insulation and an air cavity with a reflective barrier. The exterior perimeter of the floor is insulated with a continuous buried apron of frost-protected shallow-foundation R-20 polystyrene. Naturally, to achieve this level of airtightness, the house has a continuous sealed air and vapor barrier installed on the interior side of the walls and ceiling. The house design was based in part on the Passivhaus standard (note that the Passivhaus standard for airtightness requires at most 0.6 ACH50).
Other key energy features of the house include triple-pane, argon-filled, double-low-e, fiberglass-frame windows; a heat pump water heater; Energy Star appliances; and low-flow plumbing fixtures.
The designed heating load of the house at -22ºF is about 4,800 Btu per hour, and a mix of heating sources heats the house. Most heat is from internal gains that are not specifically from heating systems. Those gains include passive solar (14%), body heat (22%), and lighting and appliances (40%). Only 24% comes from an electric heater. (See Figure 1.) Marsik calculated the total annual consumption of the electric heater at about 1,120 kWh. Recently, however, he replaced the electric heater with an air source heat pump, and he anticipates that his electricity consumption for heating will be even lower next heating season.
According to Marsik's analysis, 30% of the building's total heat loss is through the walls. The second-biggest loss is through the windows and door, at 28%. Heat loss through the floor is 18%; heat loss through the ventilation system is 17%. Only 7% of the heat loss is through the ceiling.
The cost of construction in Bush Alaska has always been expensive, which is a barrier to energy-efficient building. The material costs for the Marsik-Donaldson house, including the land, well, sewage system, heating systems, HRV, and interior amenities, came close to $170,000—and that does not include the labor, much of it done by the owners. But savings on energy costs may quickly erase that premium. The average house in Dillingham—which in general is smaller than the average house in typical road-connected communities—pays about $5,470 annually for heating and electricity combined. The Marsik-Donaldson house spent about $900 in total energy costs (for electricity) its first year. That's over $4,500 in operational savings per year at current energy costs in Dillingham.
The Marsik-Donaldson house is considered net zero ready because of the way it's constructed and because Marsik wants to wait awhile on technology and see what develops. Marsik thinks that renewable energy, which could boost the house to net zero, will operate more efficiently and/or be cheaper to install. Either scenario would lower the cost of energy. Or Dillingham may develop a community-scale renewable-energy system in the near future, which would make getting to net zero more cost-effective than installing a residential system.
But to achieve low energy use takes more than meticulous building and purchasing the most energy-efficient technologies. Low energy use is also a lifestyle, a behavior, a belief system. Before the house was constructed—before the house was even lived in—Marsik and Donaldson had formed the same opinions about their personal energy use, and agreed that cooperative energy use behavior started by taking a global perspective.
Marsik believes that energy use is one of the most important issues in today's world. He sees the world's strong dependency on, and the easy depletion of, nonrenewables as making it more difficult for future generations to adapt.
"And not just that," says Marsik. "With respect to nonrenewable fuels, we are causing environmental problems during all stages of the process: extraction, transportation, and usage.
"International conflicts due to the dependence of some countries on other countries' resources are another potential big issue. With my engineering talent, I feel ethically obligated to try to help solve these problems, which is why I am active in the area of sustainable energy."
Learn more about the Marsik-Donaldson house.
Marsik's wife and partner, Kristin Donaldson, shares his environmentally conscious conviction. Donaldson helped build the airtight house and supported the project in other ways. Their demonstrated effort of living by example has become even more important, more personal, for the both of them now that Donaldson is pregnant with their first child. As parents, they hope to create a home that will be more comfortable, more manageable, and have less of an impact on the environment. Walking the walk is no longer simply an abstract contemplation; the future is on the way, and it's priceless.
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