The Foundation: Building a Monolithic Dome Using an Integrated Floor System

The Finished Product

Since a Monolithic Dome's strength comes from the building ' not its foundation ' a Monolithic Dome's foundation doesn't require the vertical strength that a conventional structure requires. In areas with slow ground movement, an integrated floor foundation is used so the shell and dome will move together. (Airform orders include detailed information. For domes larger than 50' diameter, contact MDI for special construction considerations.)

1) Prepare Pad

Use a non-expansive fill such as sand and gravel. (Check with a contractor or supplier for best fill type for your location.) Consider a vapor barrier when pouring any concrete floor. The vapor barrier can be heavy plastic under the sand under the floor, or after the floor has cured, you can apply a vapor barrier coating directly to the concrete.

2) Set Benchmark and Level Pad

Set a ground stake as a benchmark that becomes the center point and the spot to call "level." Level the pad in relationship to your benchmark.

3) Dig Trench

Just inside form boards, dig a trench to provide: a vertical concrete wall that keeps animals from digging under house; a reveal so lawn doesn't come up to floor level; an area for the ring beam. Rebar is placed in this trench, whose depth is determined by need for frost protection and/or reveal.

4) Set Form Boards

Place plywood, cut to proper height, horizontally around pad's perimeter. Attach boards with screws to wooden stakes placed about 12" apart. Check form boards and pad for levelness.

5) Conduits, Piping, Water, Sewer Lines

Utility and communication (Internet, TV, phone) lines can be placed under the slab. Copper pipes, without joints or welds that reduce chances of leakage, are recommended for under-the-slab water lines. Generally homeowners can install these provisions, but some locations require licensed electricians and plumbers. And some areas require a vapor barrier: large piece of plastic that covers the fill and prevents water irrigation through the floor.

6) Rebar Placement

Dome openings require extra uprights at their sides and additional rebar in the ring beam foundation. Lay foundation rebar in horizontal grid pattern across pad. Use plastic chairs to raise rebar off pad. In expansive soil, place additional rebar in radial pattern around perimeter. Engineering specifications and dome size determine rebar amount and size.

7) Pouring Concrete

Hire contractor to mix and pour or have able-bodies help you. Cover the floor with a plastic sheet, or use a hose to keep the concrete wet for a few days so it will cure properly.

8) Measure for Uprights

To mark placement for uprights, after floor is poured and troweled to desired smoothness but still wet, make 'X' in concrete, 5' from inside of form board and approximately 10' to 12' apart around perimeter.

9) Set Uprights

At 'X,' wet-set into foundation's perimeter pieces of L-shaped rebar approximately 4" long.

10) Prepare Keyway

Keyway is a groove dug out of the wet concrete that's approximately 1" deep and 2" to 3" wide; it surrounds perimeter where uprights are placed and locks dome shell to foundation. After uprights cure into the concrete, bend them parallel to foundation. Cover entire floor and bent uprights with plastic. You are now ready to attach Airform.

Note: The notch can be eliminated by using a rough surface like that created by a notched trowel the width of the shell for the dome to sit on.

11) Thermal Break

After the dome is constructed, a thermal break may be advisable. This can be 2" of Styrofoam or 1" of polyurethane foam applied to the exterior surface of the footing wall, then coated, backfilled or plastered.