Inexpensive

Joe wondered if all that concrete for a dome would be expensive... well, let's see:

• Assume a 30 ft diameter dome. That's 15 ft tall at the center!
• Assume that the parabolic dome is actually a hemisphere (close)
• Assume 6" thick wall at base and 4" thick at apex, for an average thickness of 5" (close)
• Use a 1 ft x 3 ft deep concrete perimeter ring beam footing (less down South, more up North) [see footnote]
• Use a 4 in thick concrete interior slab

Dome:

Surface of sphere = 4 pi r^2 = 4 x 3.14 x 15 ft x 15 ft. = 2,827 sft
Since it's a hemisphere, divide by 2 = 1,414 sft
Times the thickness to get cubic ft = 1,414 sft x 5 in. / 12 = 589 cubic ft
Divide by 27 to get cubic yards = 22 yards
Multiply times cost of concrete ($50 yard???) = $1,090

Ring beam:

Circumference of circle = pi d
Assume 1 ft. wide x 3 ft. deep x pi x 30 ft = 283 cft / 27 = 10 yards x $50 = $500

Floor:

Area of circle = pi r^2 = 3.14 x 15 ft x 15 ft = 707 sft x 4 in /12 = 236 cft / 27 = 8 yards x $50 = $436

Total Cost of concrete: $1,090 + 500 + 436 = $2,026

[I think like and engineer, so yes, these numbers are rounded off! That's OK, we're gonna double it when we're done!]

OK, we've spent two grand on concrete so far. For sake of the discussion let's assume the steel costs as much (it won't). Let's spend another grand on miscellaneous items like 2x6 lumber to frame the door and a nice little igloo style smoke hole at the top, and the plastic to keep the dirt off the concrete on the inside while we pour. We haven't insulated it. Styrofoam would be the best bet. The cost rises. So, for an entire shelter we spend $4,000 - $6,000, depending on whether you want it to be a "home" or just a place to hide out till the sun returns. I realize that this is bare bones, but it's bomb proof, earthquake proof, wind proof, and the Native American ancestors (and descendants) would be proud of you since it's a true "earth shelter". Remember, this is the total cost for the "shell". No carpenters, no concrete formwork, just honest hard work.

F.Y.I. No, I'm not building one. I'm not into domes. Give me a cave any day. I've always been a hermit! But to each his own, and the most intriguing thing about this to me is the fact that a couple of people could build one of these in a week or so (working full time) and the concrete would be cured within a month. It could very well be somebody's solution.

P.S. If I made a mistake in the math somewhere, I already know I'm stoopid, so please don't rub it in!

[Footnote: North and South for purposes of frost line are to satisfy the building code people, who won't be too thrilled about your dome to start with! These directions won't apply after the pole shift, so I guess it's a moot point, huh?]

Offered by Ron.