HASTINGS, Mich.-Tell someone that the main building material in a two-story house's outer load-bearing walls is passenger tires filled with dirt, and a likely response might be: They'd better keep the load light.
Matt and Beth Farner built a house using more than 2,500 tires in Hastings, Mich., about 35 miles southeast of Grand Rapids. The prospect that the house would ever sag or collapse is nonexistent, the Farners say.
A consulting engineer they hired bolsters that viewpoint.
``He wrote a long letter full of scientific and technical details,'' Mr. Farner said. ``Translated into plain English, it said these walls would support a building of at least 15 stories.''
The interior walls of their solar-powered and solar-heated ``Earthship'' home also are made of a recycled material: empty aluminum soft-drink cans. Like the outer tire walls, they not only dramatically cut construction costs, but also are extremely strong.
Mrs. Farner laughed as she recounted how she and her husband let guests walk on top of a 2-foot-tall inner wall. ``They just can't believe how strong it is-made from empty cans,'' she said.
The Farners open their home to one public tour and six to eight private tours per year. ``We think it's important for people to know there are ways to build a house other than cutting down trees,'' she said.
They like to promote the energy-efficient, environmentally friendly home building techniques using recycled materials that they learned from Michael Reynolds, an architect based in Taos, N.M. They read Mr. Reynolds' Earthship books and took his four-day seminar.
``A tire house is not for everybody,'' Mrs. Farner said. But even the visitors who don't plan to build a tire house see many construction, energy and living-space options that conserve natural resources while lowering costs, she said.
``We haven't turned the (propane-fueled) heater on in two and a half weeks,'' Mr. Farner said in late March, referring to a period when winter roared back into the Midwest. He attributes it to the thermal-mass insulation that the tire walls provide and the home's ability to trap the sun's heat.
The Farners' 3,800-sq.-ft. home is 160 feet long and 25 feet deep. The rear wall on the home's north side is buried in dirt, part of it dug into a hillside and the rest backed by an earthen mound. The front of the house, facing south, consists of floor-to-ceiling windows, and each room has a skylight.
The wall of windows fills the home with sunlight and close-up views of wildlife. It also provides free solar heat.
``At night, we close the drapes to trap the heat,'' Mr. Farner said. The annual heating costs are one-fourth of the bill for an average conventional house of the same size.
``There are two big advantages to a tire house,'' he said. ``First, it's a recycled material. And second, the walls are thermally massive. They're like a thermal battery charged during the day by sunlight. They release heat at night.
``In one to two hours, I could train you to be a competent tire-wall builder,'' Mr. Farner said.
Mr. Farner estimates they saved $150,000 by recycling tires and aluminum cans into walls and doing the work themselves.
Other natural resource-saving features of the home include generating electricity from photovoltaic panels on the roof and a windmill; getting water from condensation and rainwater on the roof; and using 20 cases of unopened beer cans as the coolant between the inner and outer walls of the refrigerator.
For most of the year, the electric generator rarely kicks on for the refrigerator. A flue brings cool night air into the beer-can-laden space, and the cans remain cold through much of the day.
Building homes from recycled materials and using solar power instead of fossil fuels has a huge potential impact. Forty percent of the world's materials and energy resources are used in buildings, according to Worldwatch Institute, a nonprofit research organization focusing on global environmental issues.