By Matthew Power Dome-shaped homes have been around for more than 30 years. Most people associate them with the geodesic-type structures briefly popularized in the counterculture of the 1960s. Today's dome homes have little in common with geodesics. They require less raw material and are built as one sturdy, superinsulated massing. In the commercial sector, domes have become well-respected--as storage facilities, stadiums, even schools. Yet American home buyers have strong reservations about living in what they see as a scaled-down version of Epcot Center's "Spaceship Earth."
A few dome loyalists and at least one architect hope to change that perception. Rick Crandall designed this unique, double-domed home for himself in Mesa, Ariz. But his larger goal is to change the public persona of dome systems.
"Part of the discovery I've made is that people are very interested in domes from a technical, energy-efficiency standpoint," Crandall says, "but they think domes are ugly. We did a study, and we found that if a shape is simple, Americans say, 'this can't be very valuable.' So you mix materials. You deal with shadow lines. You break up the surface and the shapes. The value goes up."
Domes offer another major advantage: durability. They offer tremendous resistance to hurricanes, earthquakes, and severe weather in general. But those qualities, for most consumers, weigh in as a bonus, not a primary reason for buying a dome package.
On this unusually quiet jobsite, builder Robert Johnson of Stetson Construction runs the show. Using unusual tools such as pressurized sprayers and blowers, he must mold those ideas into concrete form. Johnson has practice building commercial domes all over the world, so he knows the basic concepts. Nonetheless, he says, building dome homes requires special knowledge, and unexpected problems can arise.
For example, on the day scheduled for the inflation of Crandall's house, windy weather forced a delay of about a week. And every new project has a new lesson to teach--including this one.
"Before the inflation, we dug our footings and put in both horizontal rebar and vertical rebar that attaches to the dome," Johnson recalls. "Then we poured the footings. I decided not to pour the floor, because when we spray the shotcrete on the inside of the dome later, we always get a certain amount of it on the floor and have to shovel it up."
Johnson later regretted that decision, he says, because he hadn't taken into account the relatively small diameter of a residential dome. Concrete leveling tools with long handles wouldn't work in the space.
"Next time I will pour the floor first and just shovel it out," he admits.
In anticipation of the inflation, Johnson follows a careful series of steps, most notably stocking the inside of the dome with everything needed to finish the interior surface--scaffolding, lumber for framing out windows and doors, pumps, and even mechanical lifts. The reason: Anything longer than a couple of feet will never fit through the double airlock door that provides access to the inflated form.
Next, he installs an airtight corridor between the two domes, hoping to inflate both simultaneously using one pump. After a few minutes, he realizes that to reach the required pressure of 2-column inches of water, he will need two inflators, one in each dome. With the new pump in place, inflation takes only about 20 minutes. He then adjusts the rpm of the blower to regulate the pressure, along with a slide damper on the airlock door, to keep the big balloon standing tall.
"The inflators need to be left running continuously for about a month," he explains. "You can't have any power outages, or your whole roof could collapse. At first I had a gas-powered inflator backup, but then I went to a backup generator, just to be safe."
With the domes inflated and the gear inside, Johnson moves his crews inside for the dirty work.
Layer by layer
Working with a small crew of about three helpers, Johnson tackles step one, which is to build the 2x framing blockouts for doors, windows, and other penetrations.
As each framed shape is finished, he braces it against the PVC skin of the dome, usually from the floor, and checks for plumb and level. Occasionally, he screws into the block from outside the dome. Once these blocks are in place he begins to blast on the first layer of foam, which glues the framing to the PVC skin.
"I spray the first layer so that I can still see the glow of daylight coming through the PVC of the dome," he says. "Then I spray the second layer until I can't see any light."
At this point, Johnson pushes rebar hangers into the foam. He adds the remaining polyurethane foam, bringing it to a thickness of about 2 Q inches.
Rebar goes on next, a sturdy web of both horizontal and vertical pieces.
"Generally, we use #3 or #4 rebar for something of this scale," he explains. "The layout will depend on the engineer's plan. I generally use a tie wire to hold the verticals to the horizontals."
At the same time, electrical conduit and plumbing "go in" to the grid. In this case, the domes contain only conduit. All of the plumbing will be restricted to the central module, between the two domes.
As a final step before beginning the shotcrete application, Johnson attaches "depth gauges" to mark the finished depth of the 3 inches of shotcrete.
"You have to start with a 1/2-inch layer and cover the whole inside," he explains. "Then you let that set up overnight. If you try to put too much at once, you could sag the dome."
Design: The magic bullet?
The layout of this home represents the architect's answer to the resistance many people have toward domes. "People tend to gravitate toward traditional housing forms," Crandall says, "but we found that on a basic level, they react the same to a square gray box as they do to a plain dome. You have to add detail."
To accomplish this, Crandall looked at how other architects have treated domes. He wanted to invent his own paradigm--one based on traditional French chateau architecture. The center area contains the kitchen and bathrooms, while the domes house the primary living spaces.
"We're trying to play up on the round themes, yet keep the design socially acceptable," the architect says. "One problem in the past has been dealing with nonconforming rooms in a circular space. Our solution: Don't subdivide the rooms. Each dome has one big area downstairs and one bedroom upstairs. That way, when you're upstairs, all of the dome is exposed, which can be very dramatic."
The builder will frame off the central kitchen and garage using traditional materials and stick framing. Later, he will support the second floor with I-joists that are lag bolted to the concrete shell, with load bearing vertical members below.
"I'm going to spray polyurethane between the floor joists," Johnson adds. "That will help control sound between the two floors."
Once complete, the home will include curving walls of glass block, rounded showers and tubs, and curved top plates--all designed to mimic the round theme without adding much to the cost.
Despite the relative speed and economy of construction, building a dome home takes special skills--the type of skills more familiar to a pool installer than a home builder. It's easy when learning the process to make a critical error. The safest way to build your first dome, says Johnson, is to attend one of David South's classes at the Monolithic Dome Institute in Fort Worth, Texas.
South's expertise also extends into equipment. He now sells most of the specialized equipment needed to get a dome-building business up and running. Rented commercial blowers, shotcrete pumps, etc., tend to be too large for residential domes, so he sells smaller, residential-sized products. Total cost to the prospective builder: approximately $30,000.
So far, only a small group of builders have experimented with domes. "I've had a lot of contact with builders," says Crandall. "They're essentially saying they don't want to experiment. But what's going to happen is that eventually as the energy crunch hits, and there's difficulty with [storm] survivability and more talk about saving trees, I believe people will gradually turn to domes."