DOME MAGAZINE: Fall 1995, Vol. 5 | No. 1
Rumors by various proponents of dome design contend that a dome structure requires less lumber materials than a conventional square house covering the same number of square feet of living space.
Dome builders, including us, have made the claim that the dome structure requires from twenty to forty percent less lumber than it takes to frame-in a conventional square house of like floor space.
Does the dome really take less lumber than the conventional rectilinear structure? These numbers will determine once and for all how much the real difference is between the respective designs. Just how much less lumber does it really take to build a dome?
The Geo-Star
The following is a lumber list required to frame-in a 40’ diameter, 975 square foot, double walled, low profile dome, which we have termed the GEO-Star. This dome is 15 1/2’ high and is comparable in usable square feet to the standard rectilinear tract house of 25 x 40’ with 1,000 square footage of floor space.
We are making this comparison, using the 14 1/2 double wall concept, because we do know that the material list is even substantially less using this system, than the conventional square house design using the 2 x 6 exterior wall for the square house design as this has become a minimum norm in areas where energy codes are in effect. This list provides space for 12” of fiberglass insulation to provide a nominal R value of 42.
The following is a complete list of lumber, necessary to enclose this particular dome:
- 10 2 x 6 x 12 No. 2 or better
- 3 2 x 6 x 14 No. 2 or better
- 20 2 x 6 x 16 No. 2 or better
- 13 2 x 8 x 18 No. 2 or better
- 2 2 x 4 x 12 No. 2 or better
- 3 2 x 4 x 14 No. 2 or better
- 25 2 x 4 x 16 No. 2 or better
- 35 2 x 3 x 8 No. 2 or better
- 67 2 x 8 x 1/2 CDX exterior plywood
- 25 # 8p nails
The above numbers translate to 715 lineal feet of 2 x 6 at a cost about 40 cents a foot for about $286; 466 lineal feet of 2 x 4 at a cost of about 25 cents per foot or $117; 67 sheets of 4 x 8 x 1/2î plywood at an average cost of $10 per sheet or $670. Total lumber cost to frame in a low profile 44î diameter dome shell is $1073.
Conventional Frame House
Here is the comparative lumber list of material to frame in a house of comparable square feet. The building is dimensioned at 25 x 40 for a floor space of 1,000 square feet.
- 800 Lineal feet of 2 x 6 studs, No. 2 or better
- 390 Lineal feet of 2 x 6 top and bottom plates
- 22 Roof trusses, consisting of 1,760 lineal feet of 2 x 4 lumber
- 73 4 x 8 1/2” CDX plywood
- 1190 Lineal feet of 2 x 6 at 40 cents per foot $476.00
- 22 Roof trusses consisting of 1,760 lineal feet of 2 x 4 at 25 cents per foot $440,00
- 73 4 x 8 x 1/2î CDX plywood at $10 per sheet $730.00
Total lumber cost $1,646.00
PERCENTAGE DIFFERENCE
2 x 6 716 LF 1190 LF 62 1/3% +
2 x 4 466 LF 1760 LF 350% +
4 x 8 x 1/2 73-67=6 sheets or 15%
The dome has about 1,955 square feet of surface area, and the equivalent area of the square house is 2,240. This means that the square house has about 18 percent more surface area than the dome.
Given equal insulation factors, the dome will be at least 18 percent more efficient in the use of available energy for heating and cooling.
Compare
The approximate costs for materials for the dome is $1,073, and for the square house is $1,646. This represents an increase of 65% more to build a square house than a dome of similar size.
Does this have any significance in these troubled times where the waste use of the renewable resource, trees, and the critical need for housing, are prime subjects in today’s economy? I believe with a passion that by using the total cooperation of the dome industry, Buckminster Fuller’s dream of becoming the housing of choice can, most certainly, become a reality.
NOTES:
- All operable windows are Caradco®. Equivalent may be substituted
- Deck framing to be DFL #2 or better
- Exterior footings to extend to frost depth
- Bearing walls to be 2 x 4 studs at 16” O/C with double top plate; treated bottom
- Extend wall between living units to top of dome
- Optional locations for bedroom closets
- Loft framing: 2 x 4’s at 16” O/C