Many Virtues

Excerpts from an article on domes in Solar Today Magazine, by Jonathan Zimmerman

Domes embody the virtues of simplicity, economy and energy conservation, and enclose the maximum amount of space with the least surface area. It is this surface area which consists of building materials, and comprises the exterior skin of buildings through which heat is lost or gained. This is the essence of dome efficiency. ...

An entirely different construction technology offers the solution to this dilemma. This technology, known as airforming, is a method of building concrete structures by spraying construction materials on the interior of an inflated airform, or balloon. Rigid foam insulation is sprayed onto the inside surface of the balloon, steel reinforcing bars are fastened to the insulation and concrete is sprayed to cover the steel, all from the inside of the inflated form. When the concrete cures, the inflation fans are removed and an insulated, freestanding, steel-reinforced concrete shell remains. The exterior of the balloon can be coated with a variety of different colors and textures to meet individual requirements. Openings in the shell are created by not placing the steel and not spraying the concrete at the desired locations. ...

The use of an inflated balloon as a primary construction element represents a major improvement in the art of concrete forming. The cost of an airform, constructed to inflate to a specific size and shape, ranges between $1.25 to $1.75 per square-foot of surface area. The cost of conventionally formed curved concrete surfaces is about $12 to $15 per square foot of surface area. Completed shell costs range from $25 to $35 per square-foot of base floor area, not including interior construction and finishes. Comparative costs for the shell of conventional buildings of the same square footage are nearly double that. It is readily apparent that we can now build small steel reinforced concrete structures at an economy of scale formerly possible with only very large public buildings. ...

Conventional flat-walled structures must be designed with expensive moment-resisting connections and shear walls to counteract the stresses which accumulate at corners during wind and earthquake loading. With the absence of corners and resultant stress concentrations, this shell concrete structures are far more earthquake and wind resistant than conventional structures. The ability of these buildings to easily accommodate earth berm loading allows concrete shells to nestle into the landscape. Earth berming and landscaping can be sculpted against the shell structure, allowing an interaction between architecture and landscape architecture that is not possible with conventional buildings. ...

The concrete shell is insulated by the layer of foam against which it is sprayed. Hot air rises and heats the top of the concrete shell. The heat is conducted back down through the shell to achieve a steady state condition. The shell then radiates energy to living spaces below. Measurements reveal as little as a 5 degree F temperature difference between the air temperature at the floor and the air temperature at the ceiling. The temperature difference between floor and ceiling in conventional structures with little thermal mass can be as much as 25 degrees F. During hot weather, an operable skylight at the top of the shell creates a natural convection flow for warm air to rise and exit the structure. By means of this no-moving-parts fan effect, the moving air also fosters evaporative cooling, without the need for air conditioning units in all but the most humid of climates.