The challenge of learning how to build an energy-efficient home is not in the engineering and design: it’s in juggling the trade-offs. Every element of a home has ramifications on other elements. You can’t have it all, and deciding what’s most important to you demands a lot of knowledge and thought.
This was the core of the message we got from spending a day with Mark Klein and Jim McKnight, of Gimme Shelter Construction in Amherst, Wisconsin. According to the nonprofit Wisconsin Energy Conservation Corporation, which performs home energy ratings for the Wisconsin State Energy Office, these designer-builders are responsible for the most energy-efficient homes in the state. We wanted to learn some of their secrets.
The term “trade-offs” was used again and again, from site selection to economics, from basements to windows and roofing. “It’s a process of going through the choices and making decisions,” Jim McKnight said.
Trade-offs might include size and quality. A good smaller house is better than a poorly designed and built larger one, Mark said. A smaller home with nooks, alcoves, and built-in personal spaces is what delights us about old houses, he believes. “Quality is more important than quantity.”
The first consideration for how to build an energy-efficient home is the site of a home and its orientation. Mark told us about a government housing project where two homes, with exactly the same floor plans and construction methods and materials, had a 30 percent difference in heating bills (a significant number in Wisconsin’s climate). The reason? One had most of its windows on the south side, while the windows on the other faced north!
While this might seem like a no-brainer, the trade-off, in this case, would have been having the “back” of the house facing the street. With private construction, a different design could have been used of course, or a different site could have been chosen, but the same principle often applies in less drastic ways. One of their clients, who is raising sheep for profit, wanted a home in the middle of a flat, open pasture, which meant trading off any natural protection from winter’s northwest winds. (The first step on an open site is to plant plenty of trees, Mark pointed out.) Another wanted a view of a lake, which meant windows on the north side of the house. It’s rare for all ideals to be attainable, but they should be kept in mind, starting with shopping for a site.
A south slope is ideal, but what goes up must come down: not all land can slope south! Protection from prevailing winds, views, soil types, length of driveway, water table and many others similarly require compromises in most cases. Different sites have different problems and different solutions. Ideally, a home should be oriented with the bulk of its windows facing south, or within 10 degrees of south. A bias toward the east is preferred since morning sun is desirable and afternoon sun can result in excessive heat gain in summer. Attached greenhouses and sun spaces present similar problems. A sun space can “shadow” the room it’s adjacent to, affecting heating and lighting. A greenhouse can have tremendous heat loss and gain. Every plus seems to have an off-setting minus. The two have to be balanced, and every individual will do that differently.
Passive Solar Heating
A primary consideration in site selection and orientation is, of course, making good use of the sun’s heat. There are guidelines for how many square feet of window should accompany a given floor area, but these are just guidelines, Mark said. Among the trade-offs here are aesthetics, such as views and the terrain. Energy efficiency should be balanced with pleasant, healthful living conditions. Ideally, they aim for 8 to 10 percent of the total area of the home in south-facing windows.
On the east (where the morning sun can take off the night’s chill) 4 percent is considered ideal; with even less—2 percent—on the west, where solar gain can be oppressive. Overheating can be a problem in summer in a climate like Wisconsin’s, they warned. Windows on the north side are minimized.
Improving The Envelope
As basic and important as siting is, Jim McKnight considers that consideration number two when learning how to build an energy-efficient home. Number one is “improving the envelope.” Gimme Shelter uses several tricks and techniques here that have contributed to their award-winning super-efficient homes. Their constructions are, quite literally, “enveloped.” The entire structure is enclosed by a vapor barrier. (They prefer a product called Tu-Tuff, but cheaper four-mil black plastic can be used under the slab.) From under the basement or ground floor concrete slab, up the walls, across the attic and down again, the vapor barrier provides an airtight envelope. All seams are sealed with 3M vapor barrier tape, the barrier is taped and caulked around windows and doors, and plastic airtight boxes enclose all electrical outlets. Tu-Tuff is not oily, so the tape sticks to it well, and stays stuck. This leads to some unusual innovations. With conventional construction, it would be impossible to continue this barrier from floor to floor, because the floor joists are ordinarily set to the edges of the exterior walls. Klein and McKnight get around this by using thicker walls and in-setting the floor joists six inches inside the exterior walls. Mark points out that in a conventional basement there is an open space between the top of the wall and the floor above, between the joists. This is sometimes stuffed with batt insulation, which he considers ineffective.
A better method is to cut foam insulation to fit each space, and taping it a laborious and costly operation and one still lacking the vapor barrier. In addition, studs and joists offer very little insulating value, and are in effect “holes” in the insulation. (This is also one of the reasons he prefers to place studs 24 inches on center, rather than 16 inches. Two-by-six studs placed at the wider spacing use about the same amount of material and provide the same strength, but involve less labor and provide superior insulation.) Studs provide an insulating value of about R-5.5, compared to the R-30 in the insulated walls.
In addition, Gimme Shelter homes use 2×2 strapping or “band joists” fastened horizontally to the studs. This allows for even less heat transfer, and allows an additional two inches of insulation. At the attic level, an “energy heel” raises the roof at least 12 inches above the attic floor, improving ventilation and insulation. The two note that energy heels are becoming common today.
When energy conservation became a popular concern in the 1970s, the typical “solar house” was a rather plain shed-type affair with a high south side, filled with windows. Fancier ones made use of trombe walls, and some used thermal mass. This heat sink was often in the form of massive walls, or even underground bins of large rocks or other materials. Thermal mass served two purposes: reducing overheating on sunny days by absorbing heat, and releasing that heat when the sun wasn’t shining. Too often though, mass was ignored. It was heat-in, heat-out. Today’s homes have more mass, and those designed by Gimme Shelter bear no resemblance to the solar homes of the 1970s. You can have an energy-efficient home in any style you want, from contemporary to Victorian. And “mass” doesn’t mean what it used to, either.
Much of the mass in the homes Mark and Jim design is found in the walls. And this doesn’t necessarily mean thick brick or stone. A mere 1/8-inch of thin coat plaster added to the walls adds considerable heat-absorbing mass. Floors also provide thermal mass. Bare tile and hardwood floors are situated where they can absorb the sun’s rays. Today even concrete floors can be aesthetically pleasing. One trick they have used is to pour concrete between wood dividers, with the wood exposed. Another is using different finishes and colorings. Among other forms of thermal mass, one of the most popular is the masonry stove, which of course serves a dual purpose: thermal mass and heating device. But in general, “a big cube of mass in the center of the house isn’t the answer. Free-standing mass, just for the sake of mass, usually isn’t cost-effective.”
Any mass will be four times more effective if it receives direct sunlight. And as another general guideline, aim for five feet of mass for each square foot of glass. Using the temperature of the earth to moderate the temperature of the house is one tool used in the ’70s that is still valid. However, in Wisconsin’s climate, hydronic in-floor heating or considering a masonry stove plan are still required.
Insulation is a big part of Gimme Shelter’s method for how to build an energy-efficient home. They use B-I-B-S (blown in blanket system) fiberglass insulation. This is apparently one area where there are few trade-offs, since this product meets all of the partners’ expectations, which in this case includes the health of their workers. All the insulation is blown in within a few days, and the site is cleaned, so workers’ exposure to dust is kept to a minimum. But in addition, B-I-B-S has a higher R-value than batts which aren’t as dense; it doesn’t leave holes or gaps and it doesn’t sag like cellulose. (Cellulose is, however, used in attics, where sagging is of no concern.) Insulating begins even before the first cement is poured, with at least two inches of foam on the gravel base. The vapor barrier goes over this.
Then the 3-1/2 inch slab is poured. (Mark and Jim admit that insulating under and around the perimeter of the basement slab draws lots of opposition when they design houses constructed by conventional builders.) The concrete or block basement walls are framed with 2-by-4 studs, leaving a 2- or 3-inch gap between the two walls. This allows for as much as seven inches of B-I-B-S in the basement walls. Trade-off time: We wondered if our old basement, which has a severe condensation and dampness problem in hot weather, could be retrofitted. But the partners point out that in our basement heat is escaping into the ground outside the house, probably preventing freezing, and allowing water to sink into the ground. With insulation, that ground would freeze.
Drainage could become a problem, and structural frost damage could result. In other words, a basement constructed with this insulating system requires additional care in planning and constructing drainage. Above-grade exterior walls have about 7-1/4 inches of B-I-B-S, with an insulation factor of R-30. The attic gets a minimum of 16 inches of cellulose, for a rating of R-60. For comparison purposes, typical new homes in their area have R-22 walls (not R-30); ceilings are typically R-30 (not R-60) and basements often aren’t insulated at all (compared to Gimme Shelter’s R-24). Superinsulation adds about $5 a square foot to the cost of a house, but McKnight and Klein are convinced that this is a trade-off that pays.
There have been many improvements in windows recently, such as argon, low-E, and double and triple-glazed windows. (Windows with the gas argon between the panes of glass offer greater insulation.) Window quality is two-to-three times as good as it was 15-20 years ago, these builders believe. But even so, a good window might have an R-value of six or seven, compared to the R-30 of the walls, so a window is, in effect, a hole in your insulation. However, Mark pointed out, when you buy a window you’re not buying a heating system: you’re buying a lighting and ventilation system. While this in itself might be considered a trade-off, there are others. Good windows are expensive, but quality pays. Window manufacturers tend to leapfrog one another with improvements, so Gimme Shelter’s preference varies with time. They are currently using Marvin windows.
With today’s homeowner and manufacturer emphasis on well-insulated windows, Mark reported that there is less choice than there used to be. Low-E windows provide better insulation and more solar gain, but they reduce the amount of full-spectrum light admitted. The health aspects of full-spectrum light in the north, in winter might be more important than the solar gain. Some people consider full-spectrum light important to the human immune system, and an element in SAD disease (seasonal affective disorder), a not-uncommon winter malady in the north country. An argon or low-E window can reduce full-spectrum light by as much as 40 percent.
A window that reduces heat loss also reduces heat gain when you want that. So you have to consider the trade-offs again. Skylights are seldom a good decision, but light pipes get high marks. But these are more often a remodeling solution than a new house feature. Changing light throughout the day is important for well-being, and this means natural light. Besides its constancy, artificial lighting is expensive. So the number, placement and types of windows deserves careful consideration. Referring again to views, such as the house with the lake on the north side, Mark said that a view doesn’t require a large window. You can use such techniques as drawing people closer to the window with a window seat, or use other tricks to frame and enhance the view without poking a huge hole in your insulation. Window quilts are becoming a common feature in energy-efficient homes, although these builders admit that, as carpenters, they’re proud of their window trim and dislike seeing it hidden. But that’s another trade-off.
For Jim McKnight and Mark Klein, after all, the trade-offs in roof coverings are examined, galvanized steel comes out on top. They note that this is not the ordinary, cheaper utility grade with screw-down fasteners. When the fasteners are concealed in the standing seams of the more expensive version, they don’t loosen and leak as easily. The builders do concede that the cheaper type might perform well in milder climates. The health and environmental hazards of asbestos shingles are well-documented. But even aside from that, comparing the trade-offs are easy, for McKnight and Klein. Regular shingles might cost from $70 to $90 a square (100 square feet) to as much as $120 to $250 a square for a high-end, quality product.
Standing seamless galvanized steel is close to that high end, at $250 a square. In this case, roofing quality is comparable, the price is equal, but the steel wins on health, environmental and durability concerns. Concrete tile, slate, and similar roofs can cost $500 a square. Steel has a better long-term payback. “Copper makes a beautiful roof,” Mark admits, “but I’d rather see that used for other things.” A finite natural resource should be put to its best use.
Mark Klein’s and Jim McKnight’s concerns for health and well-being are obvious and great, whether they’re talking about lighting, the effects of insulation and other building materials such as paints and stains on both construction workers and house inhabitants, or the use (and misuse) of natural resources. They prefer unfinished wood siding from sustainably harvested forests. (The Menomonie tribe in eastern Wisconsin operates a forest and mill which is the source of much of their material.) They favor galvanized seamless steel roofing over asbestos shingles, for recycling as well as health reasons. They like bare solid floors, especially slate and hardwood, rather than wall-to-wall carpeting.
Such floors produce mass that tempers heating and cooling requirements, and without the outgassing of carpet. This concern with air quality and health again starts in the basement, where a radon barrier is one of the first installations. Radon gas from the earth is a serious problem in most of Wisconsin, but it can’t be detected until after a house is built. Mark and Jim don’t take chances. The radon barrier goes in, in the gravel, before the foam insulation, vapor barrier, and concrete. However, this is simply drainage tile, so it serves a double purpose. The tile leads to a sump, which is vented through the roof.
Now that you have designed your superinsulated, vapor-barrier enveloped home, you have to think about getting fresh air into it. This isn’t as strange as it sounds. As Mark explains, this is far different from having a drafty conventional house, because in this case the ventilation is controlled. Yes, ventilation is a penalty, he admits. But this trade-off between energy efficiency and air quality is a necessity he doesn’t even question.
Air-to-air heat exchangers controlled by a humidistat are one way to ameliorate the introduction of outside air into a heated home. This choice might not be the right one for energy conservation since it can involve drawing 70 watts 50 percent of the time. But in this case, he considers air quality the more important consideration. Breathable walls, such as cordwood, can help air quality. Mark isn’t sure about straw bales in this climate: he suspects that there’s a condensation point somewhere in that wall that is going to cause problems later. Vents for combustion appliances, including wood-burning cook stove, should be sealed. “You don’t want to create negative air pressure.”
However, gas clothes dryers are still preferred over electric dryers even though they don’t require venting. A new home with its paints, stains, wood sealants, glues, carpeting and perhaps new furniture should be especially well-ventilated for at least the first 12 months, he believes. His passion for air quality extends to a high recommendation of central vacuum cleaners, although that too involves trade-offs.
In a truly energy-efficient home, two space heating methods stand out: hydronic and the masonry stove. In hydronic systems, a heated fluid passes through pipes buried in the floor. If the fluid is heated by solar panels it will require an antifreeze in cold climates, but it can also be heated with a boiler. The pay-off is not only in comfort — including “perceived comfort” because of a warm floor — but also because a hydronic system can use a pump as small as 1/25 hp, while forced air for the same space might require a 1 hp motor.
And again, there is that air quality issue: Forced air blows dust. They use one linear foot of tubing for each square foot of area. Tubing for solar heated fluid usually goes deep (as much as three feet), while back-up systems are located closer to the floor surface. For zoned heating, loops should be approximately equal lengths. While 1/2-inch tubing is the convention, they are finding that 5/8-inch works better for solar applications. The system starts from the perimeter, to make better use of the hotter water. Tubing is placed closer together under windows and doors, but is not used under cabinets.
A 10-panel (480 square foot) active solar heating system in their area can reduce heating costs by about 50%. In the view of Klein and McKnight, the first use of active solar heating in northern climates should be to temper (pre-heat) domestic hot water. Any excess can be dumped in a thermal slab.
The Owner-Built Home
Typically, one-third of the cost of a new home is in labor. This is one reason owner-builders can use more labor-intensive methods such as straw bale and cordwood. Conversely, this is why most contractors shy away from these unconventional methods.
Of all the trade-offs, one of the trickiest to deal with is the law of diminishing returns. One inch of insulation is very good: that first inch gives you the most bang for your buck. Two inches of insulation is okay. But at what point is the extra inch not worth the extra cost? For many homeowners who are very concerned about the environment, expense is often secondary. (We have seen this in several Countryside and Small Stock Journal articles dealing with alternative energy: The payback period for a solar power system, for example, is sometimes only of passing interest. Using sunlight instead of earth-based nuclear energy or fossil fuels is the main goal.) Jim McKnight offered an example. One of their clients definitely did not want to use gas or electricity for heating. The solution was a geothermal system costing about $30,000.
Most people wouldn’t consider this “efficient,” but these people did. This can be a serious problem for many conscientious home-builders, who want to protect the earth but within their budget. Mark pointed out that today’s real estate values — and therefore mortgages — are based on style rather than substance. Ecological values are minimized. Long-term paybacks are largely ignored. Nevertheless, energy efficiency, durability, economy and health all must be balanced to provide a shelter that will protect both you and the Earth. Jim McKnight and Mark Klein are proving it can be done.
What tips would you share with someone seeking to learn how to build an energy-efficient home?
Editor’s Note: Prices from 2000.
Originally published in Countryside May/June 2000 and regularly vetted for accuracy.