The Earth Shelter

Reader Contribution by Douglas Stevenson
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People travel to The Farm Community in Summertown, Tennessee because it has one of the largest concentrations of “green” construction and energy efficient homes and commercial buildings you will find anywhere. One of the most innovative and ambitious examples of green construction on The Farm in recent years is an “earth shelter.” It was originally built to house as office space for one of the community’s members, and is now serving as a place for women coming to The Farm to have their baby delivered by one of the community’s midwives.

The back and sides of the structure are submerged into the side of a hill, using the thermal mass of the earth to insulate and regulate temperatures inside the building.

These three walls are built from cinder blocks filled with concrete and rebar (more mass) that have been properly treated to eliminate moisture from passing through to the inside. The block interior walls are surfaced with smooth river rock, both beautiful in appearance and adding to the thermal mass.

The south face of the building is made primarily of glass. Light entering the building in winter months strikes the cement slab and Vermont slate floor, along with block exterior and interior walls, warming the thermal mass of the entire structure.

In addition, a split design in the roof provides a row of small windows (also facing south) to help bring in ambient light.

The end result: Very little external heating or cooling is necessary to maintain an even temperature inside the building. Even without added heat, the temperature inside changes very little over night in winter months. On the coldest days when skies are overcast and there is no sunshine, a small wood stove adds supplemental heat, which again is absorbed by the building’s thermal mass.However in summer months, heat absorbed and reflected off the cement patio across the south front causes the building to take on too much heat.

To combat this, a pergola has been built across the front to support a vine which in summer months provides shade. Air conditioning supplements the cooling in order to make work conditions more comfortable.

Reflecting on what might have been done differently to improve the energy efficiency or “green” aspects of the building, one option would have been to choose a different color for the roof. The roof is sheathed with a dark brown enamel coated tin which has a 40 year warranty and never needs painting. The color green was chosen to allow the building to better blend in with the environment, important since the structure is located only a short distance below the owner’s home. However a white or lighter color would have reflected rather than absorbed heat and could have helped keep the building cooler during Tennessee’s long, hot summers.

There’s one other aspect of sustainability around this site that is worth mentioning. Directly adjacent to the home is a fenced garden. Periodically throughout the day, time can be spent in the garden, planting, weeding, and harvesting, all following the permaculture model that sees home, work and food production as an integrated system. All in all it is a powerful example of the sustainable lifestyle.

Read about other green buildings at The Farm Community in an earlier blog for Mother Earth News about my home, a recycled log cabin. Or better yet, come see these and many other great examples of green construction during one of my Farm Experience Weekends, held every year March, through October. I guarantee it will open your eyes to the potential of possibility!

Douglas Stevenson is a long term member ofThe Farm Community, one of the largest and oldest ecovillages in the world. He is the author ofThe Farm Then and Now, a Model for Sustainable Livingsold in MOTHER EARTH NEWS’ Notable New Books. He is also the host ofGreenLife Retreats, includingThe Farm Experience Weekendand workshops onorganic gardening, sustainability, and living thegreen life!

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