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Friday, January 30, 2015 |  Madison, WI: 17.0° F  Mostly Cloudy
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Our Dream Green House
How to push the envelope on sustainable design

Credit:Denise Thornton

The wind was howling on Jan. 6 as I awoke to the coldest day in 10 years in the rolling hills west of Madison. The thermometer read -22 F. The wind was gusting over 20 mph. My husband, Doug, and I suited up to venture out into the predawn.

The arctic blast almost snatched the storm door out of my thick-gloved grip. Doug hiked down the lane to the county road with our garbage and recycling. I was on a mission of mercy. The suet feeder was almost empty.

Pain shot through my fingers the instant I pulled my glove off to pry open the feeder. The sun rose brilliantly over the hill above the house, and I reached for my cell phone only to have it go dark in frozen protest before I could tap the camera icon.

Back inside, we warmed our hands on mugs of steaming tea but hesitated to dial up the thermostat for the day. Sunlight was just reaching the solar hot water panels and making bright patches on our concrete, thermal mass floor. Underhill House, less than a year old, was getting the first true test of its passive solar design, straw-bale insulation and solar in-floor heating. Eager to see how the system would perform, we decided against lighting a fire in the wood stove.

By 9 a.m. the backup propane boiler had turned itself off, and within an hour the solar hot-water panels were adding heat to a 166-gallon storage tank and warming the floors. At lunchtime, we were down to T-shirts as we climbed the ladder to our loft to watch the snow glisten and the trees toss.

Bottom line? No propane used all day. Indoor temperatures pushing 70 all afternoon. Still basking in the residual heat from the day's sun, we didn't light the stove until two hours after sunset. During 24 hours of the coldest blast our climate is likely to throw at us, we were quite comfortable with an evening fire in our wood stove and about seven hours of propane burned to keep our basement office space functional.

The seeds of our green architecture ideas go way back for Doug and me. We got married on Earth Day in 1978 in the glory days when combined federal and state tax breaks were available to offset 48% of qualifying green building projects. Within a year, we'd put a passive solar sunroom on the back of our Madison house. When we set out to build our new home, we knew that every decision would have both immediate and long-term environmental consequences. Underhill House is both our home and a laboratory for testing green shelter materials and techniques.

Sun power

The construction industry has a crucial role to play in lowering greenhouse gas emissions through job-site practices, alternate materials and lasting structural improvements that could allow buildings to operate with a much smaller carbon footprint. But practices won't change until homeowners step up and demand it.

Weighing the sustainability of every building decision can be daunting, and we took advantage of some close connections in the green design world. Our daughter, Della Hansmann, worked for WholeTrees Architecture, a firm known for its innovative approach to design and materials. Hiring WholeTrees gave us access to its enthusiastic and experienced team, and we worked with Della in a very collaborative and personalized design process.

The first order of business was to help us whittle the size of our dream house down and still further down. A second guest room, a "project" room and a music room ended up on the cutting-room floor, replaced by smaller, multipurpose space that has turned out to be plenty for two busy empty-nesters. The house is roughly 1,600 square feet.

Even though the number oUnf people per U.S. household is dropping, the average size of a new single-family house has increased from 1,500 square feet in 1970 to more than 2,500 in 2012. Reversing this trend and slicing off square footage is one of the most significant ways to lower a house's environmental impact. For us, the paring-down process has been difficult but freeing. We left a three-bedroom home in Madison with a packed-full attic and basement. In Underhill House, we deliberately cut storage space and jettisoned those things we hadn't touched in years.

Passive solar design was the next critical planning element to address. Grouping most of the windows in the south and east walls of the house allows the winter sun to pour in and warm our concrete floor all day, then radiate up into the room in the evening. But getting the window-to-wall ratios balanced is important. Without careful planning, the sun you love in the winter will be frying you in summer. Passive solar buildings like Underhill House also use longer roof overhangs calculated to let in low slanting winter light, but block hot summer daylight when the sun rides much higher in the sky.

Designing to take advantage of the Earth's seasonally changing tilt toward the sun is too often ignored in new home construction because every building site is different, and there are no cookie-cutter solar solutions. A perfect passive solar design may not be possible for every seasonal weather pattern, but a thoughtful compromise can really pay off.

Our passive solar heat is augmented by four 4'x10' solar hot-water panels and an in-floor heating system designed and installed by Full Spectrum Solar. In each room, a precise pattern of tubing was laid out in a series of separately controlled loops before the concrete floor was poured, allowing us to control the heat in different areas for maximum efficiency and comfort.

PEX tubing, a significantly cheaper alternative to copper pipe, has made radiant in-floor heating much more financially accessible in new and remodeled homes. This high-tech plastic tubing was first developed in the 1950s in a Madison laboratory. The current product is strong enough to withstand repeated heating and cooling cycles, and its flexibility makes installation relatively easy.

Underhill House can store enough solar heat for one day of comfort in the dead of winter and several days during spring and fall. During cloudy spells, the water in our PEX tubing is heated by a propane boiler that hangs on the wall in our mechanical room, where it does double duty as a domestic hot water heater. We routinely use the propane to keep our basement office space warm on cloudy days. Upstairs, the main living area is easy to heat with a small wood-burning stove.


With combined passive and active solar heat and an efficient little wood stove, we are using about 15% of the gas we needed to heat our Madison home. On a cold day, it's a luxury to bask in the warmth of the sun or to soak up heat from the wood stove. This is heat we enjoy guilt-free without cranking up the thermostat.

For natural gas customers benefiting from fuel costs that have been dropping since 2008, the payback period for installing a solar hot water system is estimated at 15 to 20 years, according to Full Spectrum director Burke O'Neal. Propane customers like us can expect a quicker payback of 10 to 15 years.

Wisconsin became the 25th state to declare an energy emergency this past January when low temperatures and fuel transportation issues caused a propane shortage, temporarily producing a spike that more than doubled the December price. At such times, solar heat constitutes not only energy efficiency but also energy security.

Air conditioning was another item that ultimately got cut from Underhill House. A/C is a huge energy suck that humans used to live without. But today, according to the U.S. Energy Information Agency, a typical household in Wisconsin consumes more than 10% of its electricity in air conditioning.

Because the north side of the house is built into the hill, we can hold some overnight coolness by shutting windows during the heat of the day. After sunset, the house also benefits from stacked ventilation, which occurs naturally as the predominantly west breezes flow into the basement windows and nudge cool air up through the house and out the loft windows to the east. Ceiling fans in the main room and our bedroom can create a breeze and pull warm air up and out.

We did find ourselves questioning our no-A/C choice as Underhill House construction began during the hot, dry summer of 2012. Would we regret this decision in a warming world? Underhill House was designed to weather temperature extremes, and we decided to trust the plan.

Insulate! Insulate! Insulate!

In both summer and winter, ultra-insulation can really make a difference in comfort and costs. Most of our walls are made from 18-inch thick bales of straw. While straw-bale insulation may not be for everyone, it is becoming more common. We liked the local and natural quality of straw.

Our straw bales came from an Edgerton farmer who sells his wheat kernels to a company that makes pizza dough. The bales contain no toxic chemicals and provide a wonderful sound barrier. A wall made from straw bales can be roughly three times as thermally efficient as a conventionally framed wall.

Aesthetically, our experience is that there is something satisfying about thick walls and deep-set windows.

A lot of people want to know if we are afraid of fire, insects or other critters in the straw bales. The answer is no. Once a plaster coating is embedded into the bales and built to an inch thick, there is no way for bugs or rodents to get inside. Animals of any kind are more likely to be roaming around in the loosely filled spaces inside conventional wall cavities. The plaster coating is not only a safety feature, it's also beautiful. Artisan Exteriors provided a hand-troweled undulating finish both inside and out. These plaster walls aren't painted, and they will never need to be.

The building inspector had no concerns at all about fire. We are actually safer in a plastered, straw-bale home. An inch of plaster provides better resistance to fire than conventional siding materials, and it is our first line of defense. Also, trying to burn a tight bale of straw is similar to trying to burn a phone book. There's not enough air in the bales to sustain a blaze.

Prairie in the sky

Perhaps our most radical experiment at Underhill House is the sod roof. The idea isn't totally unknown in this area -- commercial and public buildings in Madison are starting to add green roof systems on flat expanses. These high-tech planting-box systems are a great way to reduce runoff and keep the buildings underneath cool. We opted instead for an updated version of the Scandinavian traditional sod roof. Beneath the soil, there is a rubber membrane covering our gently sloping shed roof -- no ridges, no valleys. Below that is a truss system that creates a 12-inch space filled with Icynene insulating foam made from castor beans.

Sod roofs provide a great natural insulation that keeps your house warmer in winter and cooler in summer. Instead of transferring summer heat from a baking-hot roof surface to the interior, Underhill House captures solar power in the process of photosynthesis. In the summer, our roof uses sunlight to pull carbon dioxide out of the air as the grass grows. A relatively small fraction of the incoming light will radiate down into our house on hot summer days, and when the roof is watered by rain or sprinklers, we also benefit from evaporative cooling. Just imagine the difference between walking barefoot on sun-baked asphalt or a patch of grass.

Last summer we spent several dramatic days planting on top of the house. We worked with Prairie Nursery in Westfield for ideas about what plants could grow in three inches of screened topsoil mixed with compost and sand (a little lighter than plain dirt). We picked June Grass and Side Oats Grama Grass. Once they are established, these shallow-rooted grasses will go dormant when the weather is dry and spring back to life when we get more rain.

We get asked how we mow our roof, and everyone who has spent a weekend in Door County recommends that we put a goat up there. We don't expect to mow at all once the short prairie grasses are established. In the meantime, we are weeding, watering and scything our "prairie in the sky" while enjoying some great views.

So, do we regret our decision to forgo conventional air conditioning? Last summer there were days when we were well aware of the heat, but it was always cooler inside the house than out. We benefit from the cool advantages of building into a hill, passive solar shading, stacked ventilation, straw-bale walls and a sod roof. Living without A/C is hardly a burden.

Local sourcing

The environmental and financial advantages of low utility bills are clear, but we also wanted to build a structure that was as sustainable as possible. We resolved to use local materials and labor wherever we could. We built our retaining walls out of limestone rocks recycled from another project. We limited our concrete use by hand-packing slipform stone knee walls out of roadfill rock from a local quarry.

The bones of Underhill House are unmilled timbers from our own land. It doesn't get any more local than that. Using round timbers for timber framing is unusual, but WholeTrees specializes in that idea. It builds on the recommendation of Tom Vilsack, secretary of the United States Department of Agriculture, who recently urged the United States Forest Service to develop new markets for forest byproducts.

Many Wisconsin woodlots are overcrowded, and there is an abundance of small-diameter, round timber out there. WholeTrees has been working in conjunction with the USDA Forest Products Lab in Madison to create a structural product from these "waste" trees that could serve emerging green commercial markets.

WholeTrees started its study with tests performed on ash trees to try to mitigate the waste expected as the emerald ash borer, recently sighted in Dane County, damages the local tree stock.

Bruce Allison, registered consulting arborist and adjunct professor of forest and wildlife ecology at UW-Madison, sees this testing as the groundwork for a new chapter in sustainable forestry. Acquiring data on the load-carrying capacity of small-diameter trees, he says, will help clear the way for the use of unmilled tree stems in residential and commercial construction. "And the best part is the organic beauty resulting when the natural shape of the whole tree is brought indoors as an integral part of our dwellings," he adds.

For Underhill's structural columns and beams, we picked trees that were crowding others, damaged by severe weather or disease, or in some other way destined to improve the woods by their removal. We picked a double-trunked cherry that had been ripped apart by high winds, oaks that had just succumbed to oak wilt, and an old elm dying of Dutch elm disease. Looking at our woods this way reminded us of just how amazing the trees are: all a part of a community of self-replicating carbon-sequestering nano fiber bundles otherwise known as a forest.

For us, it seemed like an obvious choice to thin our own woods and build with those trees. We think it beats burning gas to haul in truckloads of two-by-fours harvested from clear cuts in northern Wisconsin, Washington state or China.

So what did all this cost?

As we celebrate Earth Day and our anniversary with the arrival of spring, new shoots are giving a green cast to the sod roof. We can catch a cool breeze through open windows as the sun provides radiant floor heat. We are grateful every day to the team of craftspeople who helped us make Underhill House a reality.

Our green-built house project passed the polar vortex test with flying colors, and all told, we feel warmer in the winter and cooler in summer despite drastically reduced energy use.

I'm sure some readers are curious how much this ambitious house cost to build. It wasn't cheap, but I don't think it's pie in the sky either.

It's virtually impossible to accurately itemize each project, as the material costs -- whether we're talking about windows or straw bales -- are intertwined with labor costs. What I can say is that on the whole our cost per square foot is roughly twice the national average of $125 -- the lion's share of this additional cost being the amount of craftsmanship needed for custom installation of nontraditional materials. But that was important to us; local craftsmanship is one of the things Doug and I set out to nurture.

Not everybody building green might choose this emphasis on local artisans. There are mass-manufactured green alternatives, which would lower costs. In either case, building a small, energy-efficient house will result in significant savings.

Sustainability is an ongoing exploration, and environmental costs are clearly not being fully reflected in sticker prices. Whether straw bales or sod roofs become common green-building solutions, UnderHill House serves as a reference point for other home-building pioneers.

You can read more about Underhill House at the author's blog, She and her husband will talk about their first year in the house on June 21 at the 25th annual Midwest Renewable Energy Fair near Stevens Point.

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