Build your Own geodesic dome home
Photo 1: The foundation.
PHOTOS: MATT SCANLON
The four of us spent that December 25 in quiet celebration. The next day came the party. Fifty-six people arrived to help us bring in the season, and to run their hands over the shapes and marvel at the expansiveness of the space. They discovered what Juliet and I had years earlier: a dome makes people stand in wonderment.
No longer solely a symbol of the minimalist counterculture, today's dome home can be as simple or as extravagant as you wish. Through our new home, we hope to show that a dome can be the starting point for a modern living space with character-one that is at once comfortable and awe inspiring, offering the ultimate in open floor plans, vaulted spaces, energy efficiency and solid construction.
We started with a 40-foot diameter, 5/8 sphere dome kit from Timberline Domes of Berkeley, California. It was a hub-and strut system that you assemble on-site (kit price for the hubs, struts, plywood, dormers, extensions and skylights is less than $30, 000). Since the dome shell is self-supporting, we were free to design inside what might be described as a multilevel contemporary home.
The structure of a dome shell allows for up to five natural openings around the base of the shell.You can extend the wing space out through these openings and build flat faces on them for conventional doors and windows. We took advantage of all five natural openings using extension kits. We started with a poured-in-place foam block foundation using Blue Maxx® blocks (photo I). We chose them because they had an adjustable angle corner block that was ideal for the nonstandard angles of a dome foundation. The blocks serve as forms for your concrete, then stay in place as your foundation insulation (R-40 when complete). It is the perfect way for a trained do-it-yourselfer to build a foundation.
After having a structural engineer look at our design, we put three steel beams in to support the main floor. We chose steel to allow a post-free basement/garage. Over the steel beams we built the main floor decking with TJI Silent Floor joists. These are manufactured wood I-beams that are light to carry, come up to 40-feet long, and are strong enough to hold up an elephant (photo 2). For the subfloor we used 3/inch tongue-and-groove fir plywood. Fir was recommended as being more resistant to water damage. Since it was almost five months before we had a watertight roof, this floor got soaked on many occasions. It was well worth the extra money.
With the main floor deck on, we were ready to construct the shell. First we placed three-foot riser walls on the deck. These raise the dome shell, providing more head room inside (photo 3). Timberline's dome kits are based on the hub-and-strut concept. Wooden struts (2" x 6" or 2" x 8" and up to eight feet long) are connected together with metal hubs to form triangles (photo 15), eventually creating what looks like a wire frame dome. Then studs are placed 16 inches on center across one side strut to fill in the triangles (photos 4 and 5). Plywood sheeting (be sure to get hold of both staging and a power framing nailer for shell construction) is applied to the outside to complete the shell (photo 6). We also ordered the cupola kit to provide light, ventilation and an incomparable place from which to take in the view. If you start applying the plywood sheeting from the top, you can use the dome structure to climb on as you work down. Adam developed an amazing capacity for holding a plywood triangle, the nail gun and himself on the dome structure as he nailed the sheet down! Despite his bravado, I was quietly grateful for the safety harness holding him. Once the shell was completed, we framed the extensions and dormers (photo 7), then installed the three exterior doors and 21 window units. We wanted to err on the side of having too much light rather than too little.
Although many people do their own roofing, we hired this out. With the dormers and extensions, plus the extra height created by the drive-in basement, not to mention doing the work in winter, we would either need professional help or a quick cure for vertigo.
The siding is vinyl with a stamped pattern that makes it look like cedar shakes. We mixed gray square bottom panels, white round panels and conventional wood grain panels to create special effects around windows, dormers and extensions. Here, too, we used contractors. They are used to the intricacies of siding and covering soffits and could do it much faster (photo 8).
We also hired professionals to insulate the inside of the shell with Icynene spray foam. It expands into all of the spaces behind the hubs, is nontoxic and seals everything tight as a drum (photo 9). The manufacturer recommends no vapor barrier on the inside, and do-it-yourself insulators should take note that Icynene is only available as a professionally installed product. We heated our dome that first (and very cold) winter, maintaining a cozy 65°F inside, using only the gas fireplace.
One of the major advantages of a dome is efficiency. A dome structure requires about 30% less material to enclose than a square home of equal floor space, resulting in 30% less exterior surface exposed to the weather. The curved shell gives less resistance to winter winds and creates a natural circulation inside that keeps all levels at a fairly even temperature. Our design includes open space from the main level to the cupola, but the temperature in the cupola is not much higher than that in the kitchen. In the summer, we can alter the air flow by opening the cupola windows and venting the warmer air out of the house to keep it cool.