How'd they do that?

The house we chose was a pre-designed plan called the Gemini from the Monolithic Domes plan book. The basic shape is two slightly intersecting spheres for a shape that many people would describe as a figure eight. (Or, make your own joke.) The major dimensions of the house are sixty feet long at the long axis, 32 feet wide at the maximum width of both domes. The maximum interior height of each dome is thirteen feet. The  interior square footage is about 1400 square feet. Although the house is not large, it features three bedrooms, two baths, and a large open kitchen/living area. teenygem.jpg (22469 bytes)

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Construction began, as with a standard house, by laying out a slab foundation with roughed-in plumbing. We had Monolithic do this job as part of their construction of the concrete shell. The curved shape of the concrete forms was made by curving strips of plywood to the appropriate shape and holding them in place with stakes. The site was leveled with sand, and steel rebar was built into the cement. Once you start pouring wet concrete, you can't stop or the joint between two batches will create a weak spot. The Monolithic concrete crew started this job in the morning and finished, with the help of floodlights, around 2 a.m. in sub-freezing winds as the only ice storm of the year (January 26, 2000) blew in. The pieces of rebar standing up around the edges of the slab were stuck in when the slab was partly dry, and will connect the foundation to the shell of the house.

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The vinyl-covered fabric skin of the dome (called an airform) was brought to the job site in one piece and attached to the slab with steel straps and concrete screws. The tall rectangle in the background is a plywood airlock which was used to go in and out of the dome while it was pressurized during the construction process.

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The dome was then pressurized with an electrically-powered blower which ran night and day until the dome was able to hold its own shape. This building was built from the inside.

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First, the crew used a pressure pump to spray three inches of insulating foam all over the inner surface of the airform. Areas where we don't want foam-and-concrete walls are framed off with wood (in this case a double window, on the left) and the crew simply doesn't spray inside that frame. After the foam has dried, they construct a cage of steel rebar which is attached to the pieces of steel sticking out of the foundation. This will be the real load-bearing strength of the building, supporting the weight of the concrete. Notice the extra rebar over the window openings to make them stronger.

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A similar pump was used to spray three inches of concrete over the rebar, for a total wall thickness of six inches. This is messy. In many places, devices like electrical outlets or ceiling fans had to be accommodated inside the shell. Metal conduit and junction boxes were attached to the rebar, and concrete sprayed over them. Planning ahead is important -- once something is sunk in concrete, it's there for good. The Monolithic crew did clean up after themselves before leaving us with an empty concrete cave to finish into a comfortable house.

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