The new adobes - houses constructed from earth and straw

Sunset, April, 1995 by Peter O. Whiteley

Two of the most basic materials - earth and straw - are providing the foundation for exciting new styles of thick-walled houses

If adobe walls could talk, they would tell us about the West. They would speak about a climate where sun is plentiful and rain is meagerly doled out. They would recall stories of the diverse peoples who shaped them from the most elemental of materials - soil, water, and straw. Made into bricks, adobe forms walls in the Native American pueblos of Arizona and New Mexico, in the California missions, and in the earth-tone homes of Santa Fe with their revealed vigas and inviting bancos. These buildings are distinguished by deeply recessed windows and doors, gently rounded corners, curvilinear niches and molding details, and a handcrafted appearance of timeless solidity.

Now pioneering designers and builders are rediscovering the environmental and aesthetic virtues of thick-walled houses, and building new ones with the same basic materials used in traditional adobe homes. They've found new techniques for building with earth and have revived a century-old technique for building with straw bales. The result is a gentler, "greener" architecture that relies on plentiful and quickly renewable materials.

Adobe buildings and their thick-walled successors are well suited to parts of the West where sunny days and clear nights prevail. The mass of the walls creates a "thermal lag" that slows the transfer of heat from inside to out (and vice versa) and helps maintain a balanced interior temperature.

Construction costs for the new thick-walled houses are generally comparable to those for a wood-frame house. The greatest benefit of the new homes is most apparent when you look at the long-term operating costs. It's like the difference between a refrigerator built 15 years ago and one of the more efficient new models. Greatly reduced energy costs make these homes shine.

So far, earth and straw construction styles have been used only for custom houses. They have yet to dent the mass housing market because most people are unfamiliar with the materials and techniques. But pressures are increasing to find environmentally sensitive alternatives to standard wood-frame construction. Eventually we may find that our architectural past holds some secrets to our future.

Rammed-earth construction

With one of the new thick-walled construction techniques, called rammed earth, walls are formed by compacting a moistened mixture of soil and cement in an open-bottom form that can be built upward as the wall grows taller. Though pneumatic tampers quickly compress the mixture, the solid walls rise slowly and somewhat messily.

Because it's built in layers, a rammed-earth wall exhibits distinctive strata, like a slab of sedimentary rock. Tampers compact about 8 inches of mix at a time into about 4 inches. Builders repeat the procedure until they've reached the desired height.

Some builders will plaster over a rammed-earth wall for a smoother or brighter interior surface, but others, like Tucson-based architect and builder Paul Weiner, prefer the wall's own honest and rugged texture. Weiner left exposed both the exterior and interior rammed-earth walls of a house he constructed near the outskirts of town. The walls' color and texture match the land surrounding the house, since about two-thirds of the iron-rich clay soil used in the wall comes from the site.

Although rammed-earth houses are well suited to any hot climate, they need some major modifications in California's earthquake country that add to their complexity and cost. To make a rammed-earth structure conform to building codes in earthquake-prone areas, builders usually start with a post-and-beam framework that does all the load-beating work. They then fill in the walls with rammed earth to provide mass and insulation.

Spray-on earth walls

David Easton of the Terra Group in Napa, California, has developed a way to build a solid earth wall that meets seismic requirements. It makes use of the same earth-and-cement mix used in rammed-earth construction, but centered in each wall is a grid of steel reinforcing bar that ties the wall to the concrete footing and helps it resist lateral movement in an earthquake.

In Easton's technique, which he has dubbed PISE (for "pneumatically impacted stabilized earth"), a single form wall is built behind the rebar at the inside edge of the perimeter footing. Openings for windows and doors are made with plywood boxes that mount to the form wall. A cement sprayer (more commonly used in swimming pool construction) shoots the earth-cement mixture against the wall. The 2-foot wall thickness builds up quickly, and the wall grows in 3-foot sections to the desired height.

Once the desired thickness has been reached, the surface of the wall is leveled with wooden screeds. The outside surface looks rough and rustic, but the inner walls are smoother because they were formed against plywood; they can be plastered to blend with other interior walls that might be framed with wood.