It's hard to say which produces a colder shiver: winter's low temperatures or the damage they do to home heating bills. But for Carol Young, neither prospect presents so much as a goose bump. Her heating bill in the winter of 1984-85 came to exactly nothing. And that zero bill included plenty of zero weather in Denver.
Ms. Young's house, south of the city, is exceptional, but not as much as one might imagine. There are thousands of houses that smugly and snugly respond to bitter cold with minuscule heating bills, often about $100 a year. Even the coldest climes on the continental United States push these super houses into just $200 in annual fuel costs.
They are built with a technique known as superinsulation, one that involves beefing up insulation and plugging air leaks. Young's house relies on both superinsulated and passive solar heating. A 2,500-square-foot house, it has a furnace that is a small, gas-fired unit made for mobile homes. She didn't use it at all last year. ``And we had a week that was 24 below, but it was sunny,'' she explains.
The combination of superinsulation and solar heating kept the house warm all through the siege (the sun heats her house, and the superinsulation holds the heat through three days of clouds). Young admits to using her wood-burning stove about a dozen times, but only for ``convivial occasions, not for heating,'' she says.
Enthusiasts see superinsulation as the essence of energy-efficient home design, fulfilling the promise -- but not the expense -- held out by solar energy. An estimated 10,000 superinsulated houses have been built in the United States, most of them over the last five years. Chris Granda, a residential building energy analyst, expects another 10,000 will be up as of the end of the year. They range from elaborate custom homes to modest tract houses.
Superinsulation has a number of supporters around the country.
Minnesota subsidizes superinsulated construction and teaches the techniques in vocational schools.
The Farmers Home Administration has a program to encourage superinsulation in Maine.
Canada subsidizes superinsulation and requires it in building codes.
Builders in Colorado and Montana are so confident about the energy savings of their superinsulated houses that they pay customers' heating bills for one to three years.
The Northwest Power Council, which covers Washington, Oregon, Idaho, and Montana, encourages superinsulation and offers limited subsidies.
In South Dakota, a building code that went into effect this year requires superinsulation in houses eligible for state mortgage money earmarked for first-time home buyers. State Energy Office director Merwyn Larson estimates the measure will cut average energy bills 60 to 80 percent. ``There's no reason for heat to cost more than $150 to $200 a year,'' he says. And this in a state where the thermometer notches in at -30 degrees F. during the winter.
``We felt very strongly that we should be giving these people a good home with a low energy bill and do something to improve the housing stock in South Dakota at the same time,'' says Mr. Larson. The code requires high insulation values -- R45 in the attic, R25 in the walls, R11 in the basement; air tightness; and mechanical control of ventilation. Mr. Larson figures the new code will add 4 percent to overall construction costs.
Mr. Granda traces the superinsulation trend, in part, to the chilly Canadian province of Saskatchewan, where, about six years ago, an architectural firm wanted to build a state-of-the-art, energy-efficient house. ``They thought that meant solar,'' he says, ``but they decided to soup up the insulation to keep the heat they were gaining from the solar.'' As circumstance would have it, an integral part for the solar mechanism failed to arrive by completion time. The house, however, ``performed brilliantly
without it,'' Granda says. The idea caught on, to the point where the Canadian government now sponsors a superinsulation project -- R2000 -- that subsidizes builders who use the technique.
The goal of superinsulation, says Ski Milburn, a Boulder, Colo., architect whose company specializes in solar and superinsulated design, ``is a house that requires no heating whatsoever, one that is heated entirely by body heat from the people who are in it and the waste heat from appliances.''
While that goal is attainable -- Ms. Young's house comes comfortably close -- it's also expensive. Houses that pull in with $100 to $200 annual heating bills are more practical and cost an extra 4 or 5 percent to build.
``For an extra 15 percent in building costs,'' says Mr. Milburn, ``a house can cut heating costs to zero. . . . For an extra 5 percent, it can cut heating costs by 50 to 90 percent.''
Milburn's architectural firm started out seven years ago emphasizing passive solar design as the most energy efficient, but ``superinsulation is taking on a lot more power,'' he says. ``It's more cost effective, and in a lot of the country it's much more practical. For solar, you need sunshine, and most of the US is not blessed with abundant sunshine. Generally, the colder the temperature, the less the sunshine.''
Despite the name, insulation plays a secondary role in these super-cozy homes. ``Of primary importance is making sure the house is airtight,'' says Granda, ``because in a conventional house, up to 50 percent of heat . . . loss comes from air leaking out. That holds true no matter where you build a house, North Dakota or Florida. You will save yourself a lot of money just by making it tight.''
Depending on the climate, designers then pack the walls with insulation valued at R20 to R30 -- the attic with R40 and the basement with R10-20. Since standard walls lack the thickness for that level of fiber-glass insulation, the design often requires double walls.
There are a variety of ways to seal up a house, and a number of companies -- with names such as House Doctor and Sherlock Homes -- have opened up to meet the growing demand. They generally find leaks by pressurizing the house and following trails left by a smoke generator to the leaks: It's like filling a balloon full of water to find holes.
Caulking around windows and door frames and foam around electrical outlets and plumbing holes generally plug the leaks on existing houses. For new construction, superinsulation installers usually wrap the inside walls with huge sheets of plastic before nailing up the drywall.
Jim Thompson, a Denver builder, followed a different technique in building a 48-unit, single-family development in Erie, Colo. With widely spaced post-and-beam framing, the outside walls consist entirely of superinsulated panels: four inches of foam sandwiched between wafer board and drywall, which seals the house and insulates at R30.
Young's house follows a similar pattern with foam panels in 4-by-8 sheets that were nailed to a post-and-beam frame.
Just plugging holes cuts heat loss significantly. Houses built now turn over the inside air two or three times an hour. Halving that figure with ``plugs'' is relatively simple. A superinsulated house, one designed for tightness, turns over no more than half its air every hour. Young's house reduces the hourly turnover rate to 20 percent.
Ironically, the air tightness that helps insulate a house also presents one of the biggest problems. Designing a house so that virtually all the heat stays indoors can also mean a house where most of the air stays put. That lack of ventilation leads to problems ranging from the unpleasant to the unhealthy. ``You can build a house that is literally too tight for human habitation,'' says architect Milburn.
The most accepted way of dealing with this indoor air pollution is an air-to-air heat exchanger, a device that pulls in outside cold air while pushing out inside stale air. The two pass each other in transit, allowing the exiting warm air to heat the entering colder air. ``A good air exchanger [about $200] will recover about two-thirds of the heat in the air being exhausted,'' Milburn says. ``Some of the manufacturers claim 75 percent heat recovery, but I don't think those tests would hold up in
Superinsulation may be popular, but it is not new. The first such house was built in 1940, says Granda, and ``Sweden has been building them for years; 80 percent of all their houses are superinsulated. . . . It's been mandated by code for 11 years.''
How fast it continues to catch on in the US depends largely on the builders' perspective. Big builders ``won't go with it for five or 10 years or longer,'' says Steve Andrews, a Denver home energy consultant. But, he adds, ``I do foresee smaller builders getting into it, using it to differentiate their product.''