Question: “I was wondering if there is a limit to the size of diameter an earthbag dome can have. I am wanting to have a dome with more than 800 sq ft. I would like it to be a dome because I do not want the hassle of constructing a roof, and I’m a simple person so I am only wanting to construct one dome instead of multiple ones. Any information about this would be helpful, thank you!” Tyler
Owen:
Somewhere around 20′ interior diameter is about the size limit for earthbag domes. That would be 23′ exterior diameter. That’s only 314 sq. ft. interior. No way can you do 800 sq. ft. using conventional earthbag building methods.
The largest earthbag dome at this time is the Om Dome. It’s 27′ exterior diameter. They had problems and had to rebuild part of it. Don’t risk doing a large dome like this unless you’re experienced. The dome could collapse on you while you’re building it.
So how can you build large earthbag domes? One option to consider is building the lower part with earthbags and making the upper portion with ferrocement. See drawing above. (This drawing is actually from my earthbag vault design, but it’s very similar.) Drive rebar down into the earthbags about every 24” with about 30” extra length sticking up. Make a reinforced concrete bond beam at this point for stability. Now you can make the ferrocement armature. Attach it to the protruding rebar.
You’ll need a way to insulate the dome. This could be done by stacking small bags of scoria (about 3”-4” narrower than the lower earthbags) on top of the ferrocement shell. Attach galvanized tie wire to the ferrocement armature that sticks out from the plaster and use it to secure the scoria bags. You could use some baling twine to help secure the bags.
My Earthbag Dome Instructable provides free guidelines to get you started.
Kelly Hart has extensive information about his scoria earthbag dome that will also be a big help.
Everything you need to know about ferrocement is free on the Internet.
Curious why domes tend to have no or very small window openings? Is it safe to have large and numerous windows on a dome?
Also I’ve noticed that oftentimes window and door forms on domes have arches over them. Is this to support the weight of the earth above them?
And would it be a sound idea to start a dome with larger bags on the bottom and then smaller, lighter bags towards the top? Would this provide more stability for the structure overall as opposed to having the same heavy bags on the top as on the bottom?
All window and door openings in earthbag domes will tend to weaken the structure, so the fewer the better in that regard. Yes, the arches above openings helps support the weight from above.
You are right that graduated bag size with larger ones at the bottom and smaller ones at the top is a good idea.
So in addition to the curved arches, is there anything else that can be done to allow for more and larger windows while maintaining the structural integrity of the dome?
One can insert vertical rebar stakes on either side of the openings and in some cases either interior or exterior buttresses can be made. However, the continuity of the circular pattern of barbed wire between the courses will still be interrupted.
Gotcha. So one last question is, this is really only an issue with domes. Roundhouses or even square ones would not have this issue as much simply because there would not be as much weight resting over the openings. Am I correct in this understanding?
This is partially correct, but also domes exert an outward pressure that vertical walled structures do not, so the banding with barbed wire is more critical.
Ok, I’m understanding much better now. So if I wanted to have 4 standard sized windows on a dome (say 2′ x 3′) pointing in each direction, then not only should I put rebar reinforcements on both sides of the windows and curved arches above them, but as you stated previously, it’d also be prudent and advisable to put outside buttresses underneath each window to offset the outward force, correct? And adding matching buttresses on the inside would be even better?
I’m also guessing that it’d be better to have windows that are more horizontal than vertical to lessen the number of courses that have the barbed wire interruption. So 3′ x 2′ windows would actually be better than 2′ x 3′? Am I correct in this understanding?
I think that you have a general understanding of the issues involved. Making arches above the windows also interrupts the wire bands, so in this case you might opt for using a heavy duty lintel above each window (say about 4″ thick) and pass the rebar stakes through it for security. If you did this you could probably dispense with the buttressing. For aesthetic and practical reasons, I would probably orient the windows 2′ X 3′.
Sounds good, thank you so much for your help and explanations!
Guess around 10 meters\11 yards is the maximum diameter for a single silo or dome and 12m\40ft the maximum height. Although if you’re wanting a home that large, you are better off doing it as multiple silos and or domes.
We usually recommend not making earthbag domes any larger than about 6m/7 yards in diameter. I agree that combining smaller domes is a good idea for making more space.
I’ve seen earthbag plans with 3 or 4 stories, which leads me to believe that building up is also an option, like for the ”Rainwater Towers” apartment building plan, as well as the ‘Native Spirit” and tallest watchtower plan. Thus it seems feasible to build a three or four storey house out of earthbags given the right engineering. I’m guessing you could go even taller than that, 6 to 10 floors if you use one of those old grain silos, which would be perfect for lighthouses and castles.
I live in Tn and am having a difficult time finding an engineer that will sign off on my building diagrams. Any idea how to get a building permit if Noone will work with you.
I suggest that you check in with the engineers at http://www.structure1.com as they are familiar with earthbag building and are licensed in all 50 states.
Can you do this type of construction in sections? Like making multiple arches that touch together.
It sounds like you are picturing a vault rather than a dome, and it is possible to make vaults in sections that are linked together. But the size limitations on earthbag vaults are very confined; I recommend no larger than about 8 ft. across as the base, and even with this it may need to be buttressed.
how about max size (diameter & height) for roundhouse something like cylinder
how do we make partition inside earthbag house? use the bag it self or some kind of wood? plywood, osb etc
Maximum size of roundhouses without lots of extra reinforcement: 30′ diameter
You can build any type of interior walls you want. I like stud walls because it makes running electrical and plumbing easy. Use recycled wood or wood from dead trees harvested in the forest.
3m height should be fine i guess … but for tropics do i need to make it taller? maybe 4m? is there any benefit?
3m ceilings are the norm in the tropics. Do not go higher than necessary. Instead, make sloped ceilings that direct hot air out roof vents.
Dr, I’m thinking about round house with flat slightly slanted metal roof .. so should i make it higher than 3m?
can i put bags with rice hull as insulated ceilings? just rice hull or mix with soil?
3m is standard in the tropics. No reason to go higher. Just add vents along the top of walls and one or more ceiling fans.
Rice hulls can work but be careful because in the tropics they may become rat nests. I’ve been told it’s nearly impossible to keep rats out of attics and similar cavities in the tropics. They chew through cement board, etc. because they can sense the cavity (potential nesting area) on the other side.
I probably wouldn’t bother with going any higher than 3 meters in the tropics unless you plan on having a second floor level of some kind, in which case a cupola of some sort is highly recommended so that the second level doesn’t get too hot. Remember, there’s a reason houses in the tropics lack attics.
Ferrocement, post & beam, or truss roofs will be easier than a large earthbag dome over Owen’s recommended safe size limits.
I started building a 24′ interior dome, just a single dome so that I may meet my minimum square footage required and be able to handle the project with no budget other than bags/rock and a late August start in the mountains. After some 80mph gusts moved my big arch forms, I dismantled my 10 rows and pushed it out to almost 25′ interior diameter to meet my forms new position.
Using Scoria bags that don’t achieve that solid compaction of a good rammed earth soil, there was a tendency of lower rows to roll/bulge while I tamped above. Thats the nature of big eb domes. That’s hassle, not building a roof (if you can afford it). Rebar pinning, temp bracing with bottle jacking, repositioning sections of row a Eb until it’s right. I won’t do another 20+ again. Interior walls, lofts, and built in shelving could all help buttress when needed in domework. Though once it’s bagged up to the top, especially with rebar pins, it’s super solid. But getting there in a big dome is a hassle.
Might wanna consider 100lb bags if you are set on pushing the limits.