Just outside of Durango, Colorado, sits a 2,400-square-foot house that combines the architectural design of old European timber framing with energy efficient straw and clay construction. “The main focus of building this high-efficiency home was the use of natural materials,” says home owner Katie Waller. “The timber frame works well with the natural building technology that we used.”

A key to this natural building technology in the Wallers’ home is the thick exterior walls made of straw and clay. “Straw insulates the walls while the clay gives it mass,” Mark Waller says. “Formed straw-clay walls perform best on the sides of the house where solar gain is an asset, especially in the winter. The east and south sides are great places to collect solar energy because the 12-inch-thick formed wall will heat up and keep the house warm.”

Walls made from clay-covered, straw-bales, on the other hand, are incredible insulators, says Mark. A material’s insulating power is measured by its R-value, or ability to resist the flow of heat. A higher R-value means the home will be more cost and energy efficient. For instance, the R-values of stone and concrete are 0.08 per inch and 0.2 per inch respectively, whereas an inch of straw-bale has an R-value of 2.7. “I’ve heard that an 18-inch straw-bale wall is about R-50,” Mark says, “so that’s how we built our north and west walls. The north wall insulates from the cold, and the west wall counters the heat from the summer sun.”

At the heart of the home is a full timber frame made primarily of white oak. “Oak is the wood of choice here. It’s workable, traditional and economical,” says Alan Bernholtz of Wind River Timberframes in Mancos, Colorado. The green timbers were harvested and milled by an Amish community in the Ohio Valley, and the joinery was done locally at Wind River Timberframes.

“We could have done post and beam, but we chose to go with the pure form of timber framing for the beauty and craftsmanship involved,” Mark says. “Timber framing is a natural partner to straw-clay building.”

In keeping with the theme of using natural materials, Mark and Katie finished the frame with a clear citrus oil-based finish by Land Ark to accent and bring out the grain of the wood. “It gives the wood a golden tone,” Alan says.

The Wallers live in a 250-acre co-housing community—a small, planned neighborhood of sorts—so finding help to raise the frame was no problem. “It was almost a bit chaotic at times because there were so many people milling around,” Alan says. A few days after completing the frame, it was time to begin creating the straw-clay walls and the controlled chaos started all over again. “It was just a big mud party,” Katie says. “Two solid days of slopping the straw and clay, pounding and walking in the walls to pack it down. It was fun, but you get so dirty!”

Project manager Kari Bremer, owner of Fountain of Earth Design & Construction in Bayfield, Colorado, says the combination of timber frame and clay gives the Waller home a unique look of its own. “It’s a northern New Mexico territorial style with a pitched roof, gabled dormers and adobe. And then there’s that European timber frame system,” she says. “It was a fun project to work on.”

Kari and her crew directed the construction of the straw and clay wall system, the plastering and a good amount of the interior design including the adobe floor in the sunroom. “It’s literally a very well-sealed mud floor,” Mark says. “With the passive solar design of our home, the low winter sun comes in through all those windows. The dark color and mass of the floor actually allow it to soak up and hold onto the heat from the sun.”

The sunroom is part of the open living space on the main floor that also includes a great room and dining room. A distressed maple butcher-block island separates the kitchen from the other rooms. “The island is a barn red color almost like a big farm table,” Katie says. The kitchen floor is the same hickory used throughout much of the main level.

All of the bedrooms are on the second floor. “Upstairs, we have two children’s bedrooms and the master bedroom with a walk-out deck that’s open to the sunroom below,” Katie says. “That’s our family room with a little day bed, TV and VCR.” A play loft sits above the bedrooms for the Waller children: eight-year-old Nicolas and six-year-old daughter India.

The house is heated using the combination of a hydraulic in-floor radiant system and wood-burning soapstone stove, which rests on a raised hearth that Mark built from stones collected on the property. “The stove is so efficient that, in the winter, we light a fire in the morning and let it burn out around eight or nine o’clock at night. The radiant heat from the stove pretty much warms the house until the next morning. We use the actual heating system very infrequently,” Mark says.

The exterior surface of the house is natural mud adobe topped with a dark blue metal roof by Pro Panels. “We were passionate about the choices that we made in certain finishes and other things that went into completing our house,” Katie says. “We went as non-toxic as we could on everything from adhesives and sealers, to the carpet and all plaster on the wall.” These natural clay plasters with natural pigments were either hand-troweled or applied using a technique called “alis.” “Alis is a mixture of clay with mica, sand, straw and a few other potions to create a very fine consistency that you paint on and then polish for a leathery sheen,” Kari says.

“We also had to think about what this house would turn into when it’s fallen down and gone,” Katie says. “Basically it will be nothing more than a pile of wood, straw and clay that will go back into the Earth.”

But for the time being, the Wallers will continue to enjoy the healthy home that they have created using materials directly from Mother Nature.

Bale Out: Straw Bale Construction

Banish all notions of straw houses being blown down by big, bad wolves. Straw—simply a tube of cellulose—is a structural wonder and straw-bale buildings are a natural and sturdy building alternative capable of resisting heat, cold, rain, fire and wind. Europeans built straw houses 200 years ago that are still standing. Hay-bale structures built in Nebraska have been withstanding blizzard-force winds for a century. Homes built with this renewable resource are even soundproof.

Kari Bremer, the Waller’s project manager, instituted two types of non-load-bearing straw-clay walls in their timber frame, which is the support structure that holds up the roof. Heat-resistant straw-bale walls make up the north and west sides of the house, which need the most insulation. The walls were formed with stacks of 18-inch straw bales held together by a bamboo lattice network. This exterior pinning method, also known as the “corset system,” forms a ribcage around the bales and ties to the timber frame. “It’s the strongest bale system I have used,” Kari says.

Light straw-clay walls with lower insulating power make up the south and east sides of the building that benefit from the sun’s energy. This method uses a batter of clay, water and straw to form a straw-reinforced clay mud. The mixture is tossed with a pitch fork and packed into a double-sided, 12-inch cavity made from 2-by-4 studs.

This framework, which wraps around the oak frame, is embedded in the tamped straw clay to create a monolithic and continuous wall. A fire- and insect-proof clay-plaster finish — a natural preservative for the wood and straw — completes the earthy feel of this energy-efficient home.

-Rachel Machacek