CONSTRUCTION : Designer Has Dirt on Earthen Homes
The recent fires, mudslides and earthquakes are forcing many to rethink the way contemporary homes are built. Ironically, one of today’s best construction materials is right under our feet: earth.
Non-polluting and easily available, soil is constantly being created. Much of it, such as decomposed granite, is perfect for ramming back into rock-hard walls. The construction technique, known as “rammed earth,” has been used since earliest times to create homes that are energy-efficient and strong.
Designer/builder David Easton, who grew up in Anaheim, has spent 18 years researching and developing methods for forming, reinforcing, stabilizing, compacting and finishing earthen structures for modern use. The basic technique--which has been used on nearly every continent in the world--is to compact, or ram, prepared moist soil inside a sturdy wooden form to create solid, monolithic walls.
Using the ancient construction technique with a few new twists, Easton has created more than 100 modern earth-walled projects. His company, based in Napa, is called Rammed Earth Works.
The buildings constructed with the technique include a pet hospital in Santa Inez, single family residences, winery buildings and the 3,000-square-foot home Easton and his wife, Cynthia Wright, share in the Napa Valley.
Easton, a 1964 graduate of Anaheim High School, was strongly influenced by the architecture of the California missions and by the Craftsman buildings of his grandfather, builder-designer Louis B. Easton. After graduating from Stanford with a degree in engineering, David Easton embarked on developing the processes and the documentation required to educate people about the construction advantages of the once-venerated material, earth.
“This way of building was very popular in the ‘30s and ‘40s,” Easton said. “There are old rammed-earth houses in Los Angeles and San Diego. In fact, artist Millard Sheets’ house in Claremont was constructed that way.” Renowned architects including Frank Lloyd Wright, Le Corbusier and Bernard Maybeck have designed earth-walled houses.
As Easton explained, in the years during and immediately after the Depression, building materials were scarce, but there was plenty of labor available. People were willing to build their own homes and had the time, if not the money. Underfoot was the dirt-cheap building material they needed.
“When we developed the powerful machinery to process trees quickly into lumber, mass-produced tract houses took the United States by storm,” Easton said. “These were the decades of building euphoria. Now, however, we’re entering a new era, and we want houses to be better built and to last longer. A rammed-earth house will last for centuries.”
In contrast, Easton said, “imagine our children having to bulldoze all the ‘fast tract’ houses we’re building, carting the refuse off to be buried in a landfill and replacing them with other homes which will be bulldozed.”
*
The solid, reinforced earth walls of Easton’s Napa Valley home--named 1993 Pacific Gas & Electric Energy Showcase Home--are up to two feet thick. They keep the air inside the house cool in the summer and warm in the winter. “We do not have air conditioning in our Napa house, and we don’t need it,” he said.
Good solar orientation is essential for a thermal mass building for passive winter performance. Easton installed hydronic radiant heating directly into the structural slab as a supplemental heat source. One of the added bonuses of those thick walls is almost total soundproofing, a real bonus in high density areas.
The ideal soil to create a rammed-earth house has a blend of coarse particles for strength and fine particles for binding. The ratio of coarse to fine varies depending on the soil type, but typically 30% clay and 70% sand will yield a durable wall.
Modern rammed-earth builders add 7% to 10% Portland cement to their earth mixes to achieve even greater strength and moisture resistance.
*
Easton has been developing a new method for building the solid earth walls. He’s dubbed this new technique PISE, an acronym for Pneumatically Impacted Stabilized Earth. ( Pise de terre is the French phrase for rammed earth.)
According to Easton, the PISE process uses existing technology and equipment to “shoot” a soil and cement mixture against a one-sided form. PISE is a much faster method than traditional rammed earth. It requires less than half the form work and uses powerful mixing and delivery equipment. It took a work crew only three days to complete the installation of the walls for Easton’s home.
The PISE way, Easton said, has other advantages over traditional rammed earth. Because the soil mixture is installed at a higher moisture content, it binds better with a steel reinforcing grid to create a wall system that affords even greater earthquake safety.
Existing trades are easily incorporated into the process: Carpenters set the plywood forms; ironworkers tie the reinforcing steel; electricians and plumbers install conduits, pipes and chases. Once the walls are finished, the plywood, 2-by-4s and form work can be dismantled and recycled into interior partitions and roof sheathing.
The cost of construction varies significantly depending upon the design of the home and how it is finished. Easton said the cost per square foot of rammed-earth homes he has built ranges from $60 to $200. In conventional construction, he estimated the cost per square foot is about $100.
*
The color of the exterior is determined by the soil used, with choices ranging from reddish brown to slate gray--”earth tones,” Easton joked.
The idea is to use dirt from the building site. It can be supplemented with nearby soils to get the right balance of clay and sand.
Because the color is intrinsic in the soil, there is never any maintenance or repainting. “Select a nice-colored soil and then stabilize it with cement. It will never change, only develop the soft patina of age,” Easton said. “Many of our clients even appreciate the look of unfinished earth on the interior surfaces as well.”
Those who prefer a traditional look can finish the interior walls with plaster or drywall. If drywall is used, the plywood form on the interior is left in place and the drywall attached to it. Interior walls and partitions are constructed separately, usually of conventional materials such as wood and drywall.
Once the house is constructed, it can be expected to last a very long time.
The rammed earth technique has long been common throughout North Africa and the Middle East, with many cities and villages boasting earth buildings occupied continuously for hundreds of years.
Portions of the Great Wall of China are of rammed earth, as are many of China’s contemporary houses.
A 1926 U.S. Department of Agriculture bulletin cites, among other projects, a house in Washington, D.C., built of rammed earth in 1773 and still in use.
In France, pise de terre dates to Roman times. Its use is being revitalized with work by the group CRATerre and a university-level study program in earth architecture.
Other nations also reviving their earth construction heritage are Denmark, Germany, New Zealand and Australia, especially in Western Australia, which is plagued with termites and little usable timber.
*
Among the key concerns addressed in engineering the homes for use in this area was earthquake safety, Easton said. “We used the results of extensive field-testing (California’s 200-year adobe heritage) and proven engineering principles to design what we believe are extremely dependable buildings.”
Two of the rammed earth houses constructed in Southern California--one in Borrego Springs and one in Malibu--were subjected to recent earthquakes and came through without damage, Easton said.
Contractors and owner-builders who have taken Easton’s seminars and workshops have applied the technique to buildings as small as 500 square feet to as large as 5,000.
Easton, obviously, would like to see the material being used in developments everywhere in order to show that resource-sensitive construction techniques can provide sustainable alternatives to modern practices.
“I build with earth to show what can be done,” Easton said.
David Easton will explain how earth construction can be used in luxury and affordable housing and describe the PISE method at 7 p.m. Wednesday at the Orange County offices of the AIA, 3200 Park Center Drive, Suite 110, Costa Mesa. Admission is $10 for members of Eos Institute, ADPSR or the AIA; $15 for the public; $5 for full-time students. Any homeowners rebuilding after the fire will be admitted free.
