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Sahara Sjovaettir
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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?
 
Jay C. White Cloud
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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? http://www.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/
 
Kirk Mobert
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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.
 
Jae Suzanne
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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?
 
Avalon Laux
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hugelkultur rabbit tiny house
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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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