Stingy on fuel, 'foam dome' may be home of future
| Boulder, Colorado
Move over, Buckminster Fuller. A Colorado architect-inventor has developed a dome system that may soon eclipse the now-familiar geodesic and could even begin replacing conventional buildings in the coming decade.
The architect is William Milburn, a large man with a faraway gaze, who, according to colleagues, is a brilliant innovator.
The dome system consists of a layered shell of foam and reinforced concrete sprayed inside an inflated fabric balloon. The advantages of this novel manner of construction, which Mr. Milburn calls the stratoform system, are impressive -- energy efficiency and a relatively low construction cost.
"My object was to learn how to build buildings out of pure insulation," Mr. Milburn explains.
The net result of his efforts and those of several coworkers is a system of construction that seems to have overcome the major limitations of this architectural form.
Architecturally, there is nothing new about the dome. It dates from before the Greek Parthenon. Since the 1930s avant-garde architects have been experimenting with fabric, plywood, concrete, and foam domes. But, until now, all the necessary elements have not come together.
Concrete domes have failed because of the expansion and contraction that result from being half in the sun and half in shadow. Foam domes have lacked permanence and security: They can be broken into with a knife. Geodesic domes are made of a large number of flat, triangular pieces and so require considerable manual labor to erect.
In the stratoform domes a two-inch layer of reinforced concrete provides the strength, while four inches of polyurethane on the outside protect from thermal effects and give the dome an insulating value of R-37, the equivalent of 10 inches of cellulose fiber.
Because the dome has 40 percent less surface area than a conventional structure enclosing the same amount of space, its heat loss is even lower than its insulating value would suggest. In a wood frame house and some geodesics, the two-by-fours in the walls and ceilings further decrease energy efficiency because they conduct heat more readily than insulation.
Because the stratoform dome is a continuous structure, it does not have this problem. Its "thin shell" design often makes it two to three times stronger than ordinary buildings.
Another energy advantage of the dome is the lack of seams or cracks.This eliminates the problem of infiltration of outside air, which must be either heated or cooled, depending on the season. In fact, these domes are so tight that even in dry climates like Colorado dehumidifiers are required, and owners have to be careful to keep vents open and windows cracked to keep the air fresh.
As a result, the dozen or so domes that have been constructed in this manner require 40 to 60 percent as much energy to heat as equivalently sized conventional structures. In fact, the designers have concluded that in many cases even solar collectors are not required for space heating.
Mr. Milburn's interest in energy-efficient housing was sparked by the 1973-74 Arab oil embargo. At about the same time a colleague built a foam dome, which started him thinking about the energy implications of basic building shapes.
"The dome, I realized, is the most efficient shape because, for a given volume, it has the least surface area," he recalls.
At that time, foam domes were made by inflating a fabric balloon and then spraying polyurethane on the outside. Mr. Milburn got the idea of spraying the foam on the inside instead to give it a more finished exterior.
He and his coworkers built a 56-foot airplane hangar. They coated the interior with a one-quarter-inch layer of cement-like fire retardant, which gave the architect the idea of a layered, thin-shelled structure.
Meanwhile, a patent search on the idea of spraying the foam inside the balloon revealed that he had not been the first. A California inventor named Lloyed Turner had patented the process several years before. But after building some domes 35 feet in diameter, Mr. Turner had not done much with the idea and sold the rights on his patent to Mr. Milburn.
"As we worked with Turner's [idea], we realized that it had a size limitation ," says Mr. Milburn. "He relied on the strength of the foam to support the weigt of the concrete. By the time we got to 80 feet in diameter it took 11 inches of foam, and that was uneconomical."
Mr. Milburn, who was trained as an aeronautical engineer, realized that this limitation could be overcome by using increased air pressure within the balloon to support the concrete. He has a patent pending on this aspect of the process, the granting of which depends on the patent court's interpretation of the scope of Mr. Turner's patent.
The practicality of the air-pressure approach was demonstrated with the construction of a 120-foot storage dome for a sugar firm. Theoretically, this clears the way for domes of almost unlimited size -- large aircraft chambers, shopping malls, sports stadiums, and the like.
According to John Smith of Tecton, the Colorado Springs corporation that owns the patent rights and has worked out a number of the pratical aspects of the technology, it now is selling domes of 1,500 square feet for $20 per square foot and 4,000-square-foot domes for $15 per square foot.
Ultimately, "I think we will be able to get the cost down so low it will scare you," enthuses Mr. Smith.
So far, Tecton has built a dozen domes and has plans for more. Since last summer it has been trying to find licensees in various other parts of the United States. Already it has agreements with companies in Detroit, Des Moines, Denver , and Austin, Texas. In December, Tecton tried advertising nationally for the first time -- in Solar Age magazine. The more than 500 replies it received was far more than expected.