Earth-sheltered Homes

Image Gallery The earth roof is hands-down the most beautiful roof you can build. ROB ROY

Back in the ’70s, earth-sheltered housing enjoyed great popularity, thanks in part to the energy crisis resulting from the 1973 oil embargo. Adventurous builders and researchers explored various forms of earth-sheltered building, from underground excavated spaces to surface-level buildings with earth piled in berms against their walls. People searching for alternatives to conventional building showed that sheltering a building with earth could reduce energy costs for both heating and cooling by half or more — at little or no increased expense.

Once again, America’s overconsumption of energy has made energy efficiency an important consideration in all facets of our lives, including home design. In addition, there is a new awareness among “green” and “natural” builders that we are “paving and roofing this country to death,” in the words of architect and underground-building guru Malcolm “Mac” Wells.

An earth-bermed house can reap about 95 percent of the energy advantages of a fully underground home, and adding an earth roof, or living roof, further promotes planetary health by “greening” the house’s footprint. Most buildings have a negative impact on the planet. Combining earth-sheltered walls with a living roof has the potential for the least negative impact.

Mac Wells also advocates the reclamation of “marginal” land; he says we should not build on the best, most beautiful property available, but instead take land that has been diminished by human activity and return it to greenscape. At Earthwood, our home in West Chazy, N.Y., my wife, Jaki, and I built our earth-sheltered, earth-roofed home in an abandoned gravel pit, converting almost two acres of near-lifeless moonscape to a living, green, oxygenating earthscape.

How Earth-sheltering Works

A common misconception is that earth is a great insulator. In fact, earth is a poor insulator, even more so if it’s wet. However, earth is a good capacitor that can absorb and store heat; it’s excellent thermal mass. It stores what we call warmth, but it can also store what I call “coolth,” which is, after all, simply heat at a lower temperature.

Two independent thermal masses interact in an earth-sheltered home. The first is the mass of the earth itself, over which we have very little control. The second is the mass of the building, over which we have great control through the placement of insulation. Building a house 6 to 8 feet below grade in far northern New York, where I live, is like moving it 1,000 miles to the south, into a mild winter climate much like that of Charleston, S.C. Heating is the most important energy consideration where I live, but earth-sheltering helps with cooling as well. At the depths at which we typically build — 6 to 8 feet for a single-story home, a few feet deeper for two stories — the earth temperature in our area varies from about 40 degrees in early March to about 60 degrees in late August. We can use this narrow 20-degree temperature range to our advantage for both winter heating and summer cooling. (See “Thermal Advantages of Earth-sheltering.”)