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Cob Underground?

 
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Our plans are to build an earth-sheltered cob house, eventually, in Oregon. However I've seen lots of references about how cob is not great if it's in contact with wet a lot, for obvious reasons. So I was wondering if this is a viable option:

-Steel beaming (load bearing in walls and roof) (my other half does welding) for support (3+ feet of earth overhead, so we feel we need the extra safeguard)
-On the outside part of the walls underground, and the floor - concrete and local rock, moisture sealed.
-Inside half of the walls, plus any indoor walls - cob
-*Front wall (single side uncovered by earth mounding) - 2-3ft stone base (with nice dyed concrete between), then inner core concrete/stone moisture sealed and both outside and indoor layers cob, with deep overhang.

Will this work? We are going to build a practice single-room before we move, but we are currently in San Diego so it won't be tested against constant or heavy rain (though we *will* hose down the dirt mound several times to simulate it). We are thinking that the moisture sealed concrete protecting the cob from the earth will stop (or greatly reduce) the moisture issues, while still letting the cob breath. We considered doing it all out of mortar and local stone, but we love the fluid, rounded look of cob.

*If we can't get the permits for a house without windows, we will have smaller 'outer walls' to supply windowed fire egress from the two bedrooms as well.
 
Sahara Sjovaettir
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I'm mostly worried if the concrete / urbanite / stone outer walls (the ones that are against the dirt berm) will leech too much moisture into the inner cob walls. Any thoughts?
 
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Concrete in general does not "play well with others," in the realm of natural architecture. It simple has some rather unsavory characteristics, like holding moisture. An analogy I have often shared is to think of which you would rather have on during a fall or winter rain storm, a cotton sweeter, which grabs moisture, holds it, and then makes you cold, or the unique property of the different type of wool sweaters?
 
Sahara Sjovaettir
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I was thinking I could perhaps fix that problem by applying a moisture barrier on the *outside* of the concrete (leaving the inside, and the cob layer, natural, so that it doesn't have buildup problems). Do you think that would work?

I'm not seeing any other option for having a cob house underground. If the cob touched the dirt, it would just slowly break down from rain soaking. I am determined to have cob as the inside layer of the walls plus any interior walls.

If the concrete plus sealer won't work for the layer between the cob and the earth, could you recommend something that would?
 
Jay C. White Cloud
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Hi Sahara,

Boy Sahara, you have me in a corner on this one. When I started really getting into architecture, particularly traditional and natural building modalities, it was the 1970's. From then to now, I have always had concerns with "earthship" or "earth shelters" which are all a type of "dugout" architecture.

I was thinking I could perhaps fix that problem by applying a moisture barrier on the *outside* of the concrete (leaving the inside, and the cob layer, natural, so that it doesn't have buildup problems). Do you think that would work?

No, don't even try. Any system out there that "seals" will inevitably fail and/or harm the masonry matrix.

I'm not seeing any other option for having a cob house underground. If the cob touched the dirt, it would just slowly break down from rain soaking. I am determined to have cob as the inside layer of the walls plus any interior walls.

Romanticizing a building medium is not always in one's best interest. Determination is a good thing, but don't try to make something work when something else maybe better, easier, and perhaps more applicable.

If the concrete plus sealer won't work for the layer between the cob and the earth, could you recommend something that would?

Dry laid stone on gravel trench footings, (this could be lime mortared and/or render in some cases if the need, desire, and aesthetic follows your ideal, and skill sets. This is the outer retaining wall matrix that then has a "thermal air break" between it and the "below grade" architecture. This "thermal air break" should be a minimum of 100mm (~4") but I recommend 1 to several meters (~3' or greater). This style of subterranean building method elements the need for "sealing walls" from moisture and rising damp, and provides a maintenance access space around the primary living environment that can have several functions, including but not limited to "root cellar" style storage. You will still have to deal with the heavy timber roof, which also should have "cold roof" venting principles employed within it, especially in colder or humid climates. These roof systems, (most of which are "living roofs") are a minimum of 1 meter thick up to 5 or more meters. One of the reasons for the heavy timber and advance building skill sets.

When they (dug out architecture) work, they are probably some of the most beautiful, enduring, and delightful spaces you could have as a home, unfortunately most (98% IMO) are anything but successful. They suffer ills of all types and have a minimum lifespan of maybe 20 to 40 years before these challenges make the structure uncomfortable, and/or unhealthy to live in. This is one area of natural architecture where I have seen way too much experimenting and reinvention of the wheel. To date, the only ones I would recommend, in good conscience to folks, are those built and designed in traditional methods, in historically proven environs, with clear understanding of their scope and limitations. Some of these examples would be: China's Shaanxi Province, and some surrounding regions, which still have strong examples of Siheyuan (四合院) style architecture many below ground. Underground structures are still home to between forty to seventy million Chinese in rural areas, as it has been for thousands of years. This vast number speaks to the reality of traditional timber framing and earth based architecture, which clearly defies what most Americans think architecture is, has been, or should be. There are examples of successful "dugout" methods from Tunisia to Japan, and of course several Native American vernaculars as well.

Considerations:

Understand that an underground home, successfully designed and facilitated will never be the least expensive or easiest to build, compared to other vernaculars.

Masonry of any type, natural (stone, clay brick, lime, etc.) or man made (concretes), do not respond well to "sealing" or "waterproofing" in general, and is one of the most "common sins" of neoteric architecture. You could say that if you seal masonry, it is not a matter of "if," but when it will self destruct from such a treatment.

Unless you are building in a desert biome, cob used in a "dugout" dwelling is going to have issues, and if you overcome those challenges, you will have probably expended a great deal of resources both physical and pecuniary. Well beyond the scope of some other modality of building.

Can it be made to work just about anywhere? Yes, but at what cost? Just because you can, or have figure out a way to do something, does not make it a good choice or good practice.

You will need a large budget.

Heavy equipment, and the skill sets to employ it.

Time to select and test variable building sites for proper drainage and/or it's design and construction.

More space for architectural "footprint" than usual above grade architecture.

Mixed medium skill sets in advanced masonry, and timber framing-heavy timber construction.

I always like to close on a positive, if possible, so let me share that if you follow the traditional building techniques for "dugout" and/or subterranean architecture you will be rewarded with a beautiful and enduring home. The caveat is you must not break certain principles, and understand that this is fare from the easiest way to building in most places.

Regards,

jay
 
Sahara Sjovaettir
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I've seen lots and lots of examples of underground houses that work just fine. What are the modern ones doing to seal from moisture, and why won't that work in this case? If their inner walls are dry, I should be able to use cob inside.
 
Sahara Sjovaettir
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I've been researching and I was wondering - can I use a moisture barrier between the urbanite/concrete (outside) of the walls that touch the dirt, and the cob interior? I've seen a lot of posts on how you shouldn't put a moisture barrier on your cob (it needs to breathe, of course), but it seems to me that a barrier between the urbanite and the cob wouldn't hurt the cob. Say, the type of cement-based moisture barriers they use in basements. So really, it would be a waterproof urbanite/cement wall, with a thick cob 'plastering' to make it match the rest of the interior.
 
Jay C. White Cloud
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I've seen lots and lots of examples of underground houses that work just fine.


Agreed, many do work "just fine," or at least satisfactory (just ask the forty to seventy million Chinese living in them.) This does not change the reality, that many contemporary ones built in America today are not "just fine," or will have an onset of issues that are not easily reversible without a major intervention very soon in their architectural lifespan. As a professional Timberwright, Restoration Artisan, and natural home designer, my expectation for architecture is a life span of a minimum of 500 years before any type of intervention is required other than general maintenance and 1000 years before elemental components may have to be replaced do to compromise of some fashion. NOT 20 to 40 years.

What are the modern ones doing to seal from moisture, and why won't that work in this case?


The Dugout architecture that I am aware of that I would call good practice, with excellent affect, are usually designed within a traditional format, and/or with distinct limitation parameters for the type of architecture it is. Those done in a format of "good practice," typically rely on:

1. GOOD DRAINAGE.

2. "SHROUDING," OF THE DRIED IN SPACES FROM WATER PENETRATION, MAINLY FROM ABOVE WITH LITTLE WORRY ABOUT SIDE INFILTRATION. (I know of several that actually have springs in them for cooling, and water sources)

When you speak of, "this case?" I will go back to your original query:

-Steel beaming (load bearing in walls and roof) (my other half does welding) for support (3+ feet of earth overhead, so we feel we need the extra safeguard)


You could use steel, I have not seen this done with good results yet (not to say it's not achievable if you work hard enough at it) as it usually rusts or has to be oiled - painted on a regular basis do to humidity in the living space. I will share the observation that on a global scale still today, within the Mining profession, steel is seldom if ever used as a primary element and "mine timbering" is still considered superior to what metal has to offer. Metal elements are usually relegated to "mechanical" and transient elements within the "fossorial world."

-On the outside part of the walls underground, and the floor - concrete and local rock, moisture sealed.


Perhaps a layer of foam in some applications is germane, but not "sealing" in general other than perhaps with bentonite clay in some designs. Of the biggest "fails," I have witnessed in below grade architecture is the pored form concrete (OPC) walls and other masonry units of this material.

-Inside half of the walls, plus any indoor walls - cob


I would probably use lime plasters, and lime and stone before every considering cob, except in arid regions with an average humidity of zero to no more than 30%.

-*Front wall (single side uncovered by earth mounding) - 2-3ft stone base (with nice dyed concrete between), then inner core concrete/stone moisture sealed and both outside and indoor layers cob, with deep overhang. Will this work?

No, and mainly because of the OPC, other than perhaps in a desert environment, but then I would still rely on natural materials and not something like OPC with it's very large carbon footprint.

We are thinking that the moisture sealed concrete protecting the cob from the earth will stop (or greatly reduce) the moisture issues, while still letting the cob breath. We considered doing it all out of mortar and local stone, but we love the fluid, rounded look of cob.


This is simply not a compatible system, as cob needs to have complete vapor permeability (breath) to work well, and OPC does not breath at all, especially if it is sealed by some parging of tar or other noxious solutions. Cob needs "air flow" on both sides of it to even begin to function within acceptable margins.

Regrettably, many "modern ones," are going to fail in short order do to key design flaws, biome selection choices, and a number of other issues. Again, I can not stress enough, just because we can dig a hole in the ground, or hillside and build a structure does not make it the best choice or practice. Look to the vernacular for a region, as often this is going to indicate the logical and enduring choice, with subtle variations within those designs. I agree, also that you can take a vernacular architectural style from another region that have similar biome characteristics and apply them to a different location, and it very well may work in good order, unfortunately this is seldom the case as there are subtle environmental factors that are often overlooked.

If their inner walls are dry, I should be able to use cob inside.


Dry walls are not indications of, nor do they address the air quality and general disposition of this type of construction. Humidity is often very high in these structures, especially those with passive solar atrium front fenestration, and like designs. Most of these structures have very "calm" air flow patterns when in good working order, while many others (particularly modern ones) have "stagnant air flow" due to the lack of proper ventilation and movement.

If all the elements are designed properly, and working in concert with each other, you very well may be able to employ some cob into the designs. Look to what has lasted the longest in this family of building modality, while surviving time, tectonic and climate events, and cultural shifts: Stone, heavy timber, solid rock/solid mineral soils with carved out domiciles are almost always (if not always) the key fabric constituent of architecture in the troglodyte variety. In some rich clay based soils of the desert regions, cob "dugout" architecture would and has worked very well.

Regards,

jay

This is a just a good read for anyone thinking of building below grade, just general knowledge and understanding of methods used: http://books.google.com/books/about/Mine_Timbering.html?id=Z-IJAAAAIAAJ
 
Sahara Sjovaettir
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Our revised plan is to find a good flat spot above flood lines, build, and then mound around it with good drainage - with the thought that, since it's not under the local ground line or into the side of a hill, water won't pool around it, therefore making it dry enough to be able to use cob. (With only a few feed of dirt on the sides, wouldn't that be more like earthbag with cob interior?) I know a lot of cob structures are being build in Oregon, so they must deal with the humidity somehow. After checking with the permit office and much discussion, we changed the plan from a single front wall to having several wall sections exposed (to allow for fire egress from the 2 bedrooms and kitchen), holding the dirt back with angled stone retaining walls at each section, and then putting up a frame with sheeting to make them greenhouses (kind of shaped like the outer edges of a pie slice).

So, all in all, it's come to less of an underground structure and more of a sod-roof house (1ft or so of earth) with partial burming (4 areas around the house, between 3 and 8 feet wide at the walls - 1ft thick by the roof, sloping to the ground at a 45 degree angle or so) and attached greenhouses.

Does this sound more do-able?


That leaves it looking more like this, plus mini-greenhouses around the windows, than an truly underground house:
underground-house11.jpg
[Thumbnail for underground-house11.jpg]
 
Jay C. White Cloud
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I know a lot of cob structures are being build in Oregon, so they must deal with the humidity somehow.

When the "lemmings are running for their hole in the ground from a predator...that is a good thing. When the little fellows are running for the edge of a cliff...not so good. Just because there is a larger cultural movement to build a certain way from the FAD and FASHION of it, does not mean it is a good idea, or being done in a proper and enduring way. Let talk to folks that have lived in one for 20 years or more, ask what they like and don't like, and whether they would do it again. Many I have spoken with, would not, and those that do, have a real good understanding of design and construction principles, as well as, a solid understanding of "dugin" vernacular architecture.

So, all in all, it's come to less of an underground structure and more of a sod-roof house (1ft or so of earth) with partial burming (?berming?)...

To achieve the positive aspects of "earthship," "wofati" or "dugin" building methods, and the "thermal inertia" they can provide, you will require a minimum of 1.5 to 2 meters of earth (~ 5' +); 300mm (1') is not nearly enough, and will only act as a heat sink pulling you heat from the structure.

What you are rapidly learning is this is not as easy as digging in, or piling up, should you actually desire a viable piece of architecture with abiding wall and roof diaphragms that will last longer that 30 years without major interventions.

Are you following any of the wofati post here on Permies? https://permies.com/forums/posts/list/80/26205#230136 They have some good information but still need some tweaking to achieve longevity out of there structures.

This is a friend of mine, and he is easy to contact should you want to talk to someone that has lived in a cob structure, builds them, and knows there real limitations.

http://www.small-scale.net/yearofmud/2013/10/29/cob-cold-climates/
 
pollinator
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Jay pretty much said it all..
Cob and underground, as a general rule, are not friendly, compatible concepts. This is NOT to say that it's impossible to do, just that the kinds of extra work and expense to make it happen renders it not worth doing. If you want annualized thermal storage, you need a different method, perhaps WOFAT or something similar.. There are not a whole lot of places where underground or earth-bermed buildings are appropriate.

Cob is indeed done in the rain-forests of Oregon, to good effect, Northern Britain has an ancient tradition of cob building with VERY wet winters, some parts of Africa (and Asia) where vernacular mud buildings exist, traditionally get torrential rains. In these buildings, the cob is WELL above grade, foundations are built like drains and roof eve-lines are extra wide.
 
Kirk Mobert
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I understand that this (beautiful) building:

Is a bit of a problem child.. It (reportedly) leaks pretty badly.

Photographing well does NOT insure comfort or practicality.
 
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I built a cob wall in Northern California (rainfall 75 inches annually at the time). This work is very labor intensive and I spent a lot of time with workshop labor and then paid labor to finish it. It was gorgeous. My partner at the time was lamenting about the regular linseed applications to protect it, so I hesitated on treating it one fall and after the first rain the whole thing fell in one fell "whoosh". It was about 20" long- and protected us from hwy noise. It reversed any dreams I had about building in this region with cob. I am working with burlap- crete now and built a 75 ft fence in 3 days 5 feet high by myself for 250$ and am going to start a small dugout project to test my burlap-crete construction in the wettest climate in California... Using 9000 psi rapid drying cement with water harvesting/drainage. Curious about the water holding nature of calcium aluminate cement... anyone have any experience?
 
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Sahara Sjovaettir wrote:Our plans are to build an earth-sheltered cob house, eventually, in Oregon.



I know this thread post is an old post, but as it was recently bumped up, I happened to see it. I was just wanting to know how the house turned out, if you were able to make an earth sheltered house work, and if so, what did you use for it? I have been wanting to combine an Earthship with a Cob or Earthbag design. I love the design of both, and both have their pros and cons.

I hope you were able to figure out how you wanted to build your house, and hope it turned out well!
 
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Hi guys, I've had similar thoughts of finding a way to combine a earth bermed back wall with cob construction. It would be cool to have a vent that ran through the berm and looped back into the house for a passive a/c system.

My idea was to build the foundation up, timber frame the roof, then build up your cobwalls in that then created dry space, maybe use a different material for the back wall where the berm comes in if necessary.

THEN when you bring the earth berm in use dry dirt and throw a giant pond liner over the whole structure including the berm. Bury it one more time and grow some herbs.

What do ya think?

 
pollinator
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What about using earthbags for the underground house?
 
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Hi there, reading your comments, you seem to know your stuff, so I just want to ask, would cob built around a load bearing geosidic dome frame be suitable to build underneath or into the side of a hill, with only a thin layer of top soil to blend it in with the natural landscape?, would pond tarps draped over it be good enough water resistance, if adequate drainage is built around it etc?, the max dome size would be 16 ft diameter by 8 ft height, or thereabouts, I dont know much about building, but would like three geosidic dome frames, to be used in some way to build and support three shallow dugouts without concrete, or in a sort of pond basin style dugout for all three together, with only a thin layer of top soil, to blend it all in with the hills etc, would there be a way to make this work?, and could it be done cheaply?, I dont want to buy timber, cement, or anything like that, at maximum, prefab culvert pipes or whatever to help with drainage if nessesary, but I really just want to build it myself with natural materials over time on the cheap, as well as is possible, it's not a home I'm building, more a hikers bothy style shelter, I'm in southwestern Scotland, and take inspiration from skara brae, a very wet, windy, and inhospitable place, with houses dug into the ground using stone blocks as support thousands of years ago, thats pretty much all I'm looking for, with modern knowledge of natural materials etc, a survival bothy / glamping pod kind of deal done DIY, though I do hope to make an earthen greenhouse / wahilini in similair fashion nearby if possible, anyway, do you have any recommendations based on what I've told you?, I'm not looking for any connection to the grid or modern convenience etc, just safe secure geosidic domes, blending in just enough with the landscape so as to be mistaken for hills, so not very deep overall, and room for sloping to distribute any unnavoidable soil weight better, Is this possible?, what materials and building methods should I use etc?, any advice would be appreciated, thank you. B.
 
pollinator
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Ventilation: cob requires airspace/airflow on both side of it, how would this requirement be met with an underground/bermed wall
Water: cob requires a stem wall to keep them dry and also huge over hanging roof to keep them dry, how will you solve this problem a wet dome roof or underground walls

Load bearing geosidic: Lets pretend you don't really need cob on top of your dome you just want 2inch of course sand to grow some sedum in to have a green roof, this green roof might also accumulate snow, How much would this weight. What is the load bearing capacity of your geosidic dome. Once we have that we can work backways to see how much snow+green roof substrate+cob+berm it can hold up.  

 
Barry Thomson
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I'm not sure of exact load bearing yet, I'm still looking about, but a cheap climbing frame you can buy for children, holds between 1000 pounds to 3000 pounds of weight, if I bought a prefab UV stainless steel kit, it would probably be much greater, concrete panels with steal frames and wire mesh, constructed into geodesic domes, can survive hurricane force winds, earthquakes, several feet of snow, and even falling trees, as noted in one companies profile history, but I'm just looking to get a sturdy steel or equivelant frame, perhaps with DIY supporting wire mesh, and some diy panels / filling material, either home made or prefabricated, whatevers best for the situation, so the range is broad, and I dont have the know how to give an accurate answer, but I did pull some key notes off a general geodesic structural integrity study on cadre, which came up with a 353 psi to 1228 psi max stress loads for a wooden frame geodesic greenhouse.

According to an online calculator I used,

353 Psi = 50832 Pound/Square Foot?

1228 Psi = 176832 Pound/Square Foot?

But I'm not sure if that's correct, it sounds alot for a wooden framed greenhouse lol, but here are a few of the paragraphs from the page.

"The sample structure is a 30 foot diameter, 4-frequency, icosahedron geodesic dome made from a wood frame of standard 2x6 lumber. The dome is intended as a greenhouse and is clad with polycarbonate panels which transfer external pressure loads to the wood frame structure but provide little structural support to the frame structure. Once the load sets have been developed using the panels, the loads will be re-distributed entirely to the frame structure and the panels themselves will be structurally neutralized or removed.

"The maximum stress in the panels is 450 psi vs. 1260 psi for the component model.This difference is because the panels automatically have clamped edges by virtue of their fixed connection to adjacent panels across the struts. That is a consequence of the plate finite element definition and cannot be easily worked around. The real structure of a strut and panel type dome is not likely to have clamped edge fixity so the component model would be a much better estimate of the real stress. Rank and color again, but this time rank on Beam stress with Von Mises stress. The maximum stress in any beam is 353 psi as compared to 1228 psi for the frame model. The 1228 psi is taken from the frame-only model results (see the previous table of von Mises beam stress above under the Case 3 column). This difference is the result of the panels which support the beams both vertically and laterally all along the beam due to the panel's in-plane stiffness. If one actually builds a integral structural panels with rigid structural interconnection then using the full model with panels makes perfect sense, but with cases where they are simple non-structural glazing panels (or even fabric) then separating the solutions into frame-only models and component panel models would be the recommended approach. The main idea is to use engineering judgment to set up the model and components in ways that most closely represent the actual structural configuration."

again, I'm not sure what kind of weight loads I'll get for a 8 foot diametere to 16 foot diameter UV stainless steal frame kit, but I'd imagine it's fairly high, though I may consider wood if cheap enough, using wire reinforced cement panels etc, with the correct steal frame, can support backfilling a dome house up to 4 feet deep without modification, as demonstrated on an ai dome house, and with modifications, can safely be buried completely - https://www.aidomes.com/berming-or-burying/

but again, I dont want to use concrete or expensive materials, just the steel frame kit, or a similair prefab structure?, though I have considered other possibilities, like using earth bag construction too, I could probably build an earth bag root celler for a few hundred pounds, but I'm curious if a decent geodesic frame could work in tandem with other types of earth building, like earth bag construction?, to make my little holes in the ground a little bit safer overall, the dome acting more as emergency redundancy or whatever, and perhaps with the option of modification into a walipini greenhouse, or somthing like that, as I would be curious to see how well a dome walipini could work?, but generally, I'm looking for three basic structure types, root celler, a small living space, and an earth sheltered greenhouse of some kind, earth bags fit the bill best overall, but the materials for three structures will likely cost a bit?, so I'm hoping, with a strong prefabricated frame, I could build such in and around a hill area, or somewhat onto / and or beside the strong redundancy - emergency inner frame, in a modulated manner, to reduce the labour and costs overall, the labour atleast, though costs is still up for grabs I guess?, depending on the materials, but anyway, that's the general idea.

I could build an earth bag root celler for peanuts, right into the side of a hill, blending it into the landscape, and if I wanted, a simple earth bag bunker, could support a half sunken greenhouse, or I could just build that right into a slope following common practices, but that still leaves the living space, which i would like to ensure is atleast structurally sound / a little bit safer overall, and perhaps better able to be insulated or waterproofed, up to a more reasonable / slightly more comfortable extent, so that's why I'm wondering about dome frames, how i might be able to use steel framed geodesic domes, in tandem with other earth building methods, while utilising trench sloping and benching teqniques, and a bit of earth bag / rammed earth support work, or even simple lime and stone work etc?, leaving cob aside, the inner dome could be plastered with other coatings, to make it feel a bit more homey, and more weatherproof, if nothing else, smoothed, painted, lined with shelves, rather airy / permeable to start, and easy to add venting too etc, much better than sand bags, only really needing to worry about the minimal topsoil areas weight sloping above it, having the walls shored about via other means all around it, further, the geodesic panel spacing of the inner frame, requires less material to fill, it Is its own free standing structure, not weighing a whole lot, requiring no foundation, and much less wood / prefab paneling overall, also, I think this configuration, could pottentially make creating ventilation holes and such much simpler I would imagine?, as the space between the frame is initially naked, until its otherwise covered or filled with suitable materials.

At the cheaper end of things, I doubt that 1k to 3k of integrity, will support a four foot dugout and light soil cover, but still, I'm generally thinking of finding a nice balance Point in multi technique construction, somwhere in a hilly area, first digging a sort of pond dugout feature, in alignment with the surrounding land scape, placing my three domes in a semi circle near or facing eachother, and only minimally adding top soil, with a living roof like you say, in a manner that would give the appearance of little hills within the greater hillscape, if dug out in a sloped basin, the entrances could be small perforated culvert / risers perhaps?, or somthing like that, angled upwards to line up with the slope of a slightly deeper bermed section at the front?, and perhaps utilising a DIY French drain system, or a bit of local gravel?, though other than the run off / drainage, that's all optional, the geneeal idea, will be a series of altered sloping angles, and trench benching teqniques, rammed or rounded off perhaps?, and shored up with additional earth bag construction for strength, to prevent cave in, and reduce overall soil pressure, leaving the inner dome mostly free of surrounding weight, my domes could be placed in three such sections, structurally strengthened in some fashion or other themselves?, leaving the rammed earth / benched / earth bag surrounding walls secure, I'd backfill just enough soil to create living roofs, in alignment with the general landscape, I think this has some feasibility?, but such will require time, and a lot of digging, even if relatively cheap, so it may be better just to slot my builds neatly into stronger slopes on the hillside?, placing a few earth bags as up as security in the hill, and covering whats left sticking out just little bit,, with a thin coating of living material / and or grass, than to try tampering With loose souls?, but anyway, I'm just theorizing, to give you some idea of my build requirements.

sorry I cant be more specific on load bearing, but for very cheap, I can immediatly order a small dome climbing frame, between 1000 to 3000 pounds of integrity, if that gives you a starting point, which though relatively small in strength, could be combined with trench sloping and benching teqniques, earth bag support construction, and a sturdy set of prefab wire mesh supported panelings, of one sort or another, though DIY panels could also do in a pinch, if the primary soil support is a surrounding outer earthbag box, which I think is the best option?, the dome just needs to offer a little additional emergency protection, to act as a sort of emergency redundency, or failsafe so to speak, with a smooth and permeable inner surface to plaster and ventilate etc?, but regardless, as the cadre analysys shows, even a well designed wooden frame, can withstand much greater loads, and I could shell out on a half decent kit if I needed to, but what's the fun in that?, some designs are 10 k, some are 60 k, I'd rather use a cool thousand gbp at the most if I could manage it lol, less if possible, that kind of money is better spent elsewhere, since it's mostly a fun hobby project anyway, I'm not going to live in it on the grid style, but either way, I hope this is helpful, atleast you will have a better idea of what I hope to achieve overall, I appreciate / thank you for the time you took to respond, cheers, b.

here is the link to read it if your interested - https://www.scribd.com/document/206668595/CADRE-Analysis-of-Geodesic-Dome
 
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As S. Bengi implies, cob is not going to be able to have any part in a structure such as you describe.

If you want something that blends into the landscape, stone would be the obvious choice for wall structure, with timber for roof structure and modern waterproof covering. Low side walls and a post or two in the middle to give a spacious ceiling would be most efficient and also shed water best. A geodesic dome type frame would have to be very robust to hold any earthen wall/roof load over time. What material resources do you have on site, and how much area do you have available to gather from? The local materials would work best for DIY, and probably be much more attractive to glamping clients than a partly concealed space age dome.
 
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You were writing at the same time as I was. These more detailed ideas give some more basis for response. One thing I note:
"The maximum stress in the panels is 450 psi vs. 1260 psi for the component model."
This has nothing to do with the strength of the materials, but the load placed on them. "Stress" is what a structure needs strength to withstand. The full panel design spreads the loads more evenly and causes less stress in individual parts, while a simple frame structure concentrates stress in the frame members. The stress is in compression in the wood frame parts, not the roof/wall load that can be applied from outside.

An earth covered structure will need to stand at least 150 pounds per square foot of roof/wall per foot of earth thickness, and I would double that for a safety factor where failure means death. Dry soil generally weighs maybe 100-120 pounds per cubic foot, but add water or stone or snow on top, and 150 is more reasonable. Domes are very strong when evenly loaded, but like eggshells can fail under much smaller loads if unevenly stressed. A 16' diameter dome with a foot of earth on it would be holding a total load of around 40,000 pounds.

Your talk of earthbag or other structures around a dome seems very wasteful. If an earthen structure can support a load at all, it needs to do so reliably or it will someday fail, probably unevenly, and crush a geodesic dome inside it with random uneven loads. I would go with solid materials in the first place. You seem very enamored of geodesic domes, and for certain purposes they can be efficient and effective. Buried structures with heavy side loading require a different sort of strength.
 
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Let me know what you think of this earthbag design instead




 
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I would leave a geodesic dome/frame out of any equation for an underground/earth-bermed structure. The PSI loads depends on how much soil is being used, how much water gets into the soil, how much snow on top, and freezing conditions can cause frost heave in adjacent soil. I've only ever heard of monolithic forms used for domes that have soil added, not a geodesic frame. It seems really dangerous if anyone would be inside it for any length of time, but you could start by asking companies which sell domes what if any type of earthen load they are rated to handle. Perhaps I'm wrong and they get you the proper info, but I would guess they will all say their domes are only rated for a certain snow/wind load only.
 
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I wish you the best of luck with your project.
Here are a few principles to keep in mind any time you consider building below grade:

1) Water moves underground. It does this in deeply mysterious ways which we as surface-dwellers barely comprehend. It responds to the pull of the moon; it responds to bedrock faulting; it freezes; it thaws; it heaves. It is always under pressure. This pressure is considerable. There is a reason why most underground housing is located in desert climates. Can you do it in a damp place such as Scotland? Sure. But you have to understand: The water is there, and you cannot make it go away.

2) You can make there be less of it. You will absolutely want to line your excavation with a heavy duty curtain drain. This is not “optional” as you suggest above. It is critical to the structure functioning at all. You need a curtain drain, and you need to backfill your walls with loose gravel and rubble, and you STILL should have a moisture-proof membrane between that backfill and the hillside itself, because water will come out of that hillside not only oozing, but under pressure.

3) You should not expect any drainage system to make your structure “dry.” Water under pressure IS going to get around your waterproofing membrane at every seam and every pinhole. Your membrane and drainage system is there to lessen the hydrostatic pressure exerted on your building. It won’t eradicate it. So this affects what materials you can use. This is why everyone is telling you, for example, not to use cob. I would go a step further and suggest you not use earthbags filled with any sort of expansive soil, because as the moisture in the walls waxes and wanes according to its own law, a clay soil, even one confined within an earthbag, is going to move. A loose gravelly soil might work, or boughten gravel fill, or road base, which is many sizes of crushed stone and fines and compacts nicely. All of these will do their own draining, and remain dimensionally stable when wet. Clay soil won’t. For the same reason, I’d be wary of timber or other organic materials anywhere near being in contact with the hillside: they WILL be damp, and they will rot. Do not, for heaven’s dear sake, put strawbale underground. (I see you have better sense than to suggest this, but I have seen people try it. It turns to black sludge, every time.) Most modern underground houses are steel and concrete. Steel, as others have mentioned above, tends to rust out. The smartest solution for Scotland may be the traditional one you reference: dry stacked stone, with water able to pass freely through the joints, never becoming trapped to build up pressure or freeze. That would work. It is still going to make a high-humidity living space. You won’t want to put things in there which are suceptible to growing mold. Combustive heat does help dry things out some. A woodstove cures many humid ills, but not if hikers will only be using it occasionally during the cold, damp months.

4) I’m with everyone else who has commented so far: You DO need to calculate loads and spans before loading up a living roof. There are some more lightweight growing mediums that can accept roots while lessening the dead weight; unfortunately, they’re probably not local, on-site materials. If you’re using local soil, get someone with professional experience to sign off on your plan. An earthbag dome can be self-supporting and bear a lot of weight, yes, but only within the strictures of certain geometric forms, and only with a fill type that compacts firmly and remains dimensionally stable when wet (not clay). Your life might be easier with upright walls and a more standard roof. Play with a few different ideas. Whatever you choose, you will need something to keep water from the sky out too, and hopefully to direct it well away from the walls. I have seen underground builds where they built up their walls, backfilled (with membrane outside of drain rock), stuck a very sturdy flattish roof over that, and then covered the whole with pond liner, which then extended beyond the backfill entirely, so no rain water was directed straight down into the drain. Then growing medium and sod.

5) I’m no engineer, but just eyeballing it, pretty sure a geodisic dome made of 2x6s isn’t sturdy enough for this job. I could be wrong.

Hope this is helpful.

P.S. Regarding the extremely photogenic “problem child” pictured above: according to their (helpful and inspiring) website detailing their building process, they covered that living roof with heavy duty plastic (inevitably going to get punctured, re. Murphy’s Law), which had SEAMS because the shape of the roof is so irregular. Like a bermed wall, a soggy living roof also exerts hydrostatic pressure, which can push water uphill quite some distance, no problem. Where I live, we have the same trouble with ice dams on shingle roofs. Try not to put ANY seams in your roof, unless the whole roof is open to the air and steep enough for all water, including snow, to drain downhill freely. In my opinion, if you’re going underground, it does have to be heavy-duty pond liner, and it does have to be continuous.
 
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There is a great book about which deals with the design aspects.
I am trying to find it again.
Here is an interesting site which does not have design criteria but is still resourceful
your-new-underground-house
Its from the Underground Space Center at the University of Minnesota
 
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Dome Kit: does the manufacturer ANYWHERE suggest the structure is appropriately designed for being subterranean? That should answer THAT question.

If dome design is your desire, perhaps the newest form of dome building would suit - Aircrete.

This requires little to no special skill, equipment or large amounts of manpower. Based on what I have seen, ideally you would first attend the course (a week?), and after that it is forms, concrete and soap bubble machine.

The one I saw being built was in Hawaii, a location KNOWN for heavy, consistent, daily rain.

 
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