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"Dome homes are efficient, withstand hurricanes, tornadoes"

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Dear Jim: I watched television during the Florida hurricanes. It showed a unique dome home that survived a direct hit. I have been thinking about building a geodesic dome home. Are they also energy efficient? - Ned B.

A: I saw the same television show and the superstrong dome home was built using a unique construction method. Many of the same reasons these homes are so strong also make them the most energy efficient house design. In nature, nearly all animals also build round and domed nests, dens and homes.

This home was built by first pouring a circular concrete slab. An airform (bubble) is attached and sealed to the slab. The airform is often made of PVC-coated nylon or polyester film. The shape of the airform is designed to create the size and the shape of the dome house your family desires.

Large fans pressurize and inflate the airform. Once inflated to the proper shape, several inches of polyurethane foam insulation are sprayed on the interior surface. Openings for many windows, doors, skylights, cupolas, etc. are made in the dome. Reinforcing steel wire supports are placed against the insulation and this is covered with a thick layer of smooth concrete.

Another insulating foam/concrete construction method uses triangular panels common to geodesic dome homes. The panels are made of thick polystyrene insulating foam. They are covered on the exterior with a layer of fiber-reinforced concrete and optional drywall on the interior. More than 50 percent of these home are owner-built with little previous experience.

A temporary wooden dome frame is built. Each panel has a channel along its edges. Reinforcing steel is placed in the channels and then filled with concrete. This forms a sealed concrete exterior except for windows and doors. The lumber from the temporary frame is then used for interior wall studs.

The more traditional geodesic dome homes use standard lumber to build insulated triangular panels. These are assembled creating the self-supporting dome shape. A steel hub-and-strut method can also be used to create a geodesic frame which is later insulated and covered with plywood or OSB sheathing.

If you prefer a somewhat more traditional looking dome home, you can add rectangular extensions to the main dome home in the center. As you deviate more from a true dome shape though, it loses energy efficiency and strength.

The spherical shape is the key to a dome home's energy efficiency. A sphere has the least surface area for a given interior living space. Less surface area means less energy loss (gain during summer). Winds flow smoothly over a dome. This minimizes pressure differences from side to side resulting in less air leakage. The open floor plans are also ideal for heating/cooling.

Instant Download Update Bulletin No. 869 - list of nine manufacturers of geodesic dome home kits listing construction methods (hub and strut, hub and double strut, concrete channel frame, sprayed concrete), size ranges in square feet, six floor plan layouts, several exterior diagrams, general specifications and features on some floor plans.

Dear Jim: I am taking your advice and adding more attic insulation. I have a lot of old batt insulation with a vapor barrier. Since the existing attic insulation does not have a vapor barrier, can I use this? - Jen W.

A: There should be a vapor barrier under the existing insulation to block indoor moisture from migrating into it. If moisture gets into the attic insulation, it can condense during cold nights and soak the insulation.

If you will be doubling the insulation thickness, then you can use your batt insulation with the vapor barrier down. It will keep the insulation below it warm enough so moisture will not condense on its vapor barrier.