Large earthbag dome insulated with bags of scoria/lava rock.

Large earthbag dome insulated with bags of scoria/lava rock.


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.


Comments

How to Build Large Earthbag Domes — 7 Comments

  1. 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 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.

  2. 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.

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