Hello, This is my first post, and I am excited to find these forums.

I am building a 20 foot dome on top of a 6 foot high deck in my yard, as a fun house for my daughter and wife, and storage underneath for myself.

I live in Bozeman, MT, in the middle of town, so codes really limit what I can do, and I'm pretty sure I've maximized my fun capabilities within code.

Anyway, my plan is to sink 12 foot posts into concrete, with 8 feet sticking out (frost line is 2 feet). At the six foot height, I plan to build a deck, with a two foot railing/knee-wall. On the railing/knee-wall, I want to set up a 20 foot 3v dome on top of foam, secured to each post with pipe straps. It will be 1" electrical conduit. This will then be sheathed in white vinyl plastic on the lower 3/4 of the dome, and clear polycarbonate on the upper 1/4. Eventually, as we have enough money, I want to wall-up the lower portion of the deck, with plywood, and traditional siding, and a patio door. Once we have walls up, I want to build a rocket mass heater, and use the lower portion as a workshop, and garden shed. I will store long lengths of boards and pipe in between the deck joists.

So I came here with the purpose of receiving tips and advice on my plan. My main area of concern is how to make the bottom of a 3v dome flat? I want to steer clear of a 4v dome as it requires more pipe, and more types of cuts. Also, would a galvanized 8" pipe, buried in sand, and run into a seating area around the perimeter of the building be adequate enough for heat? I am not looking to make this a livable space, but I want it to be comfortable. Also, I am expecting this to be be a 3 season fun house. Would this kind of heating be ok for use in fall and spring in zone 4/5 with temps from 32-80 degrees? How big should my posts be if I am looking to support a deck, dome and at most 10 people? I was thinking that I could use a 4" x 12' post because I will have a post around each corner of the outside of the dome, meaning roughly 15 posts. The inner part would also be supported by another ring of posts because of the 20' span. The center would be a stairwell going up to the deck. I was thinking of using brick pavers as the floor (I have a lot of these materials I accumulated over time, so I would like to use them), and some free composite decking I found on CL for the deck.

Any tips for the following things would be MUCH appreciated:
-Venting
-How to attach the pipe to the deck railing at the posts
-How to make a 3v dome flat along its equator 9I saw the Russian site which can calculate this, but I don't speak Russian)
-Rocket mass heating tips (length width of a max-run underneath a seating area, and if I can use sand as a thermal mass)
-How big my posts need to be to support 20 foot circle of decking (composite), 10 people, some furniture, and a dome weighing ~300 pounds.

Any other critiques and advice would be great! Thanks for a great forum! Mike in MT.

http://drazium.com/mustard/dome/index.html

http://www.desertdomes.com/tips.html

http://www.growingspaces.com/

Growing spaces greenhouse style vents are the answer for ventilation. The automatic vent openers are cheap at harbor freight.

3V domes are almost level at 5/8 or 3/8 of a dome, not exactly half. 5/8 gives nicer headroom at the edges of the dome.

Think about putting in 15 posts instead of 12, it will be much easier to tie into the dome (although much harder to build the deck). Maybe 16 posts would be a good compromise for approximating round and easier to frame the deck.

Thanks for the reply! After drawing out my plans, and drawing up a CAD of the dome, I don't want to get in trouble with the city, so I am rethinking the height of my building. The good news for me is that my job is much easier now. What I plan to do is to build a deck within the dome, and put a 5/8th on 4 foot posts. (This is all based on my calculation of 5/8ths of the diameter of the sphere being: (((5/ *20) + 4 = 16.5' ).This way, even if it isn't level, I can straw bale underneath it, I don't have to tie in each post to another inner ring, and I don't have to make all the complicated cuts which would have been involved with that. So I will be building a 6 foot deck as a perfect square inside the dome. This way it will be protected immediately from the elements as well, so I don't have to save up to build walls on the outside.

What would be the best sheathing for this I figure for now, I will put clear polycarbonate on the uppermost section of triangles, and to save money, put white vinyl on the lower portion of the dome, with some windows I will fabricate from acrylic. What else do people do with conduit? I was thinking double sided tape to secure the vinyl, and then waterproof UV protected tape (like Eternabond for RV's, but the cheaper version) on the seams to waterproof it. I am aware that I will have to pull this all down in a few years when it decays from UV exposure, but hopefully by then we can afford the polycarbonate all around the dome. The tape will be the most expensive by far, but I found an acceptable price for it online. I can hang a wooden 1x2 window from the conduit without putting much stress on the structure, and I will put about 4 of them at the top, and 4 at the bottom. I will just use 4" duct in the knee walls, to bring in air, and eventually build a cupola with a permanent square vent at the top, to pull some cfm's, creating a vortex around my inner deck, and keeping it cool. These vents will be pre-warmed for the colder months by my rocket mass piping, which will run around the perimeter of the wall.

Any suggestion on the fan size (and dimensions if you would happen to know them) for a 20 foot dome sitting on a 4 foot post? Also how would one frame out a door for a dome like this. I am going 4 feet down, and I am sure this would be strong enough for a door, and even a patio door, without any support at the top. The only puzzle I have with this is how to tie the conduit into the door?

Thanks again for the reply, I have found some useful stuff on the links!

I can't help you with the sheathing. That is where I got stuck and stopped thinking about building a dome.

used billboard vinyl for the lower section (has got some toxic paint on it), and look at Shelter Systems for connectors and layering tech.

they found it is much more robust to layer, than to try to seal.