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how can I have my cob  RSS feed

 
Max Guenthner
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I live Wyoming where -30 temps aren't uncommon, strong winds, and large amounts of snow. I'm wanting to build a new house out of cob but don't think an all cob house will work. I love everything about cob and I have to have it. How can I have my cob house with the climate I'm in? Any help is greatly appreciated.
 
Dale Hodgins
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Location: Victoria British Columbia-Canada
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Woodchip clay can look like cob,  but it is much more suitable for your climate.

 Another option would be to build some cob interior walls. Build more conventional exterior insulated walls.

 Cob loses its green credentials quite quickly,  if used in a situation where much more heating fuel is required.
 
Max Guenthner
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I haven't heard of wood chip clay. One of the things I love about cob is the look of it and how you can shape and form it. Looks like I'm out of luck of the exterior cob looking house. If I just do cob on the interior with a regular exterior and insulation, will I run into issues with it not being able to breathe and causing problems while its drying.
 
Dale Hodgins
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Do it in the summer with windows and doors open. Or do it during the heating season, after the building is in use.

Many interior cob structures have been added to regular homes. Be sure that weight bears on a solid footing, not weak wooden floor.
 
Jay C. White Cloud
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Hi Max,

If I may, I would love to expand on Dale's comments (which I couldn't agree more with.)

When we "fall in love" with a building style or over "romanticize" it in some fashion, we often start down a path that leads us away from the logic of traditional vernacular system....like cob.

Cob is a "traditional system" yet employed out of context or modality, then it is out of place and/or fails to perform as desired.

Now, with that said, I feel that this project could very well become a traditional "earth based" structure. I would, suggest looking at all the "climate zone" similar to yours, and what is built there that fits your sense of aesthetic?

I will share a perspective (it is subjective as I specialize in "folk architecture" of the Middle East, Asian and other Regions) that the most enduring and longest lasting "earth based" architectural forms are not cob alone. The oldest (aka most enduring) are stone, timber and earth. So, on that note I would then look to the Mountains of Korea and Northern Japan, or perhaps parts of Eastern Europe.

For sake of conciseness I would use a Japanese Minka Farmhouse as a "base line form." It is an all natural building, stone and raised earth foundation, and can have extra think wall systems for additional insulation like "ligh cobb" (aka clay slip straw or wood chip) infill methods, or a mixed matrix of something like mineral wool board, wood planking, and wattle-daub infill. This is just one of many examples available to this projects region that may serve the desired effect, and needs at that same time...

Regards,

j

 
Max Guenthner
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I appreciate all the insight. My climate zone is about a 3b and I haven't really found any earth based homes in my climate zone.
 
Max Guenthner
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My climate zone was based off of the USDA plant hardiness map
 
Jay C. White Cloud
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In Wyoming, there are some "earth lodge" structure of Native culture, yet these would not necessarily lend themselves readily to modern design parameters and living styles. As for zone 3 (and that range) there are many examples around the globe from Hokkaido Japan, through the Himalayas (mix of stone/timber/earth) and then into Siberia (much colder in sections than Wyoming,) and Northern section of Eastern Europe. Most, I imagine, may not be in the purest sense "just cob," yet many incorporate "cob infill" and plastering systems. Hope that helps a bit more...
 
Max Guenthner
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Thank you for all the information. I will do some more research and see what I can find.
 
Terry Ruth
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Your in building code climate zone 7, parts of the west state in 8. Goggle IRC building code climate zones for a map. On a scale of 1-8 your are in the two coldest climates in the nation. Zone 3 folks hang out on the beach in winter while you freeze your arse off The requirements are just a tad bit different than agriculture ....The first thing to do is find out what codes are being enforced. There is big push to reduce fossil fuel emissions so codes will have min R-Value requirements. The problem is they do not recognize mass benefit as they should for it's ability to reduce HVAC loads by heat storage, shifting loads from peak hours etc.....IECC (International Energy Code Council) : and others give an r-value of 5-10 which is inaccurate and misleading

Looks like this states uses IBC 2006 which has some low r-value outdated min you can look up: https://law.resource.org/pub/us/code/safety.html

Or, you can build in an area that has no energy code check local jurisdictions.

In cold climates COB needs a thermal brake as in a core or outsulation such as what many have done with foam. An Engineer can calculate the conductance and resistance for a 100F temp gradiant over a thickness not a problem. If you add a core like many do with rammed earth,etc, and/or outsulation that resistance can also be part of the equation that would render an min thickness on both sides of the core. On both sides of core use concrete protection boards w/wedge or wall ties. The resistance number that results can be knocked down by ~ 30% due to mass benefit. The cost of HVAC should drop to justify the upfront cost of the insulation and foundation yielding more comfort and health benefits and higher resale value than your neighbors.

Roxul makes a Comfortboard IS 3" thick R-12 @ ~ $2.25 SF and you will need two staggered layers @ r-24 min to keep the wall down to less than 30" thick and a costly wide/deep foundation. It is rated for ground/soil contact, foundations, has a compression strength 70xs higher than foam and will not crack like foam at 25% deflection, inert, high perm and drainage, etc.

Crunch the numbers or hire an Architect/PE and your dream home may come true

 
Marion Kaye
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Location: Essex, UK
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I lived in a cob house for about ten years. night time winter temperatures were typically below -30C, with lots of snow.
Dealing with the snow? We had flat roofs, so after a snow fall, before going to work, the snow had to be pushed off.
Heating? We only had korsi/kotatsu, very cosy, sometimes indirectly supplemented by a cooking stove. Possibly not as green as rocket heaters, but then again it might be greener, as we weren't heating space.

eta the (traditional design) cob house was much more comfortable in both summer and winter than newer brick/concrete buildings.
 
Terry Ruth
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Marion Kaye wrote:I lived in a cob house for about ten years. night time winter temperatures were typically below -30C, with lots of snow.
Dealing with the snow? We had flat roofs, so after a snow fall, before going to work, the snow had to be pushed off.
Heating? We only had korsi/kotatsu, very cosy, sometimes indirectly supplemented by a cooking stove. Possibly not as green as rocket heaters, but then again it might be greener, as we weren't heating space.

eta the (traditional design) cob house was much more comfortable in both summer and winter than newer brick/concrete buildings.


Validates that COB works in cold climates thank you for the real life valuable info...It is all about a U-value myths(that are a function of thickness, ratios, density, MI, PI, that may or may not need a thermal break depending on gradient and calculations), that nobody has any quantifiable data on just guessing and opinions. "flat roof" when all odds are against you made it work, now that's permaculture at it's finest, kudo's to you!

eta the (traditional design) cob house was much more comfortable in both summer and winter than newer brick/concrete buildings.


Certain clay's done right are the mother hen of natural building construction surpassing wyths of brick and concrete(ICF's, SCIPS, etc), higher MI than wood and less labor and better MI than lime, unless they are adobe....as for the future as more professionals realize it's ancient lost property's it will become mainstream.

Great post needs an apple for your dedication and 10 years of experience living in one, most that have all the "answers" do no have.

Max, if you are really interested in this email me I can design and model a COB home in cold climates no problem, or consult but my time is not free. I live in a near same climate zone and we service and build homes in it everyday, check my blog and website.

MI= Moisture Index(max holding capacity, acting as a "mainstream Class 1 vapor barrier") as ASTM tested.

Otherwise follow my details I offered on your garage thread free of charge in support of the site: If anyone challenges the "lime base" I recommend look at the Lime Associations test info on using it at as a "Natural Class 1 barrier" I call manger vs plastic.

Yes, permies lime and clay beats out mainstream plastic and foam "vapor barriers" ALA has proof: http://lime.org/documents/publications/free_downloads/lime-based_mortars.pdf

 
Ben de Leiris
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Location: Hinesburg, Vermont
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Max,
I'm in the same boat. I built one mostly cob house and I was hooked. In the next few years I'll be building in Colorado, where it will be plenty sunny but still has cold winters. Milder winters than you, but still a cold climate. Straw bales are great and all, but they just don't do it for me like cob does. What I think about doing is a wall that looks and acts like cob, but is primarily composed of strawbales. Basically I'd stack bales in whatever shape I want but instead of trying to curve the bales, I'd just fill the wedge shaped gaps with cob. Then add cob inside and out to fair out the curves. That would also add lots of thermal mass. Or maybe have some cob columns to support the roof, filling in with bales anywhere they could be easily incorporated. I'm sure a strategy like this would sacrifice some insulation. But with enough of the wall area having bales inside, maybe not too much.
The other thing I consider is building two thinner cob walls with insulation between. I know others have talked about this but I haven't seen much on real world attempts. Maybe two 8" walls with 6" between, filled with cellulose, wool, whatever you want. I'd want to tie the walls together frequently with small lengths of tree branches, scrap lumber, bamboo, rebar, etc. The total wall would be thicker than a normal cob wall, but it wouldn't really be any more actual cob.
Don't take either of those as advice, they're just ideas I want to experiment with. Jay and Terry sound like they have much more knowledge than I do on the subject.
 
Rebecca Norman
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Location: Ladakh, Indian Himalayas at 10,500 feet, zone 5
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If you're in a dry climate and you are willing to make your cob walls thick, I would add to those above who say you'll be happy with it. I've been living with low-tech rammed earth houses in a hard heating climate for over 20 years. Our rammed earth is technically probably considered cob in forms. We have good basic solar heating designs with most windows on the wouth walls that are either exactly south or up to 15 degrees east of south, and in our case we add a seasonal greenhouse on the south side from October to May. It works great for us. If our windows and woodwork didn't leak like sieves, and if our roof had decent insulation, we might be up in normal American house temperature ranges, but our woodwork is just terrible, our roof insulation is just a cutesy experiment with garbage, and we still do fine. Some rooms go down to 12C at night in the coldest month (54F) which really feels a bit too chilly, but after a few days it starts going up again. I'm sure you'll have tight windows, roof insulation, and a backup heating source so it'll never go that chilly for you in Wyoming.
 
Terry Ruth
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1. Structurally, COB needs to be thick enough to handle loads....A baseline is 300 mm (12"). It cannot take alot of compression load, as in high levels of snow and a heavy weight roof so it needs to get thick which adds cost to the foundation. 2-6 PSF compared to a 3000+ PSI OPC concrete wall ~20-50 PSF. In high winds and earthquakes it needs a support structure especially at top and corners, less weight at top to resist shear (take your hands and rub them together that is a shear plane, clays do not do that great in shear can be much lower than compression).... Rebar in part is used in concrete for this purpose and tension. Steel can take 80,000(construction grade) - 300,000 (stainless) psi of compression, bearing.

2. Physically, less is more. Finding the right thickness is difficult. Dry climates need less since clay moisture index or storage compacity requirement is less, that is given the same type of clay....If one used kaolin it needs to be VERY thick even in dry climates, magnesium bentonite less, sodium bentionite or "swelling clay's less". They are just as many horror stories of too much mass in the wrong places and wrong climate zones, over heating homes, or cold walls, high humidity, swelling and shrinkage from the wrong clay's, cracks, bad ratio's, stains, water damage, microbials, etc....same with straw and clay or lime renders.

The problem with "u-value" or "r-value" of just looking at conductance of heat transfer through a medium such as clay for thermal bridging, is it does not account for the other methods of heat transfer, convection, radiation, phase change (internal, hidden). Take a steady state source of radiant heat like a heat gun point it at the COB measure the temp on both sides you just conducted the u-value or r-value test, what is known as a 'hot box" test.....Now lets get real add some wind, rain, pressure gradients, freeze-thaw, humidity, pollution, etc....Now try and simulate that in all climates around the globe in a lab. Not going to happen! Now perhaps we see why International building code gives it(concrete) a simple r-value of 5-10 depending on thickness, because it is too complex otherwise. Ideally, it is best to have just enough thickness to get a small exchange of heat from one side of the wall to other to keep it dry, and phase change to create heat or cooling in the wall that only gets better in high humidity. We'll I have been apart of that hot box testing model( very expensive software in the tens of thousands per license and steep learning curves) and lab simulation in multi-million dollar labs, BSC (Building Science Corp has to a lesser extent). As a result, we now have what manufactures should put on labels "effective" in situ r-value that has dynamic affects. Knock down fiberglass value 10-40%, loose fill cellulose 10-20%, mineral wool 3- 5-%. That is what it takes experience wise to understand it. Now go out to forums get millions of opinions in super impressive big worded post on the subject now you have popcorn entertainment who needs redbox

I run the fluid dynamic models at my job since they can afford me, and my home designs because I can. Most homeowners cannot. So there are some steady state and "dynamic" models in this industry that are rarely accurate (WUFI, few others) Needs a good seat jockey, trash in trash out. I cannot predict this behavior without the proper tools(models, lab, etc) so how do people think they can guess? I tell you what, consider yourself very lucky if you guessed correctly. Most that put hundreds of thousands into their homes could end up being eaten alive by very uncomfortable sick homes, and to tear it out and start over very expensive.

COBs outer skin or surface is not the correct pore size to handle liquid water, it needs to be modified to make it more durable, especially when exposed to the elements of nature.

Ben, I do not see anything wrong with the insulation core, COB renders at varies thicknesses given it meets the two minimum requirements I noted above. One issue with cellulose blown is it need to have the right density ~ 3 lbs ft3 and it can settle over time, so can straw. The rigid mineral board I suggested has a compression value of 750-1200 PSI (5-10) PSF which is much better than foam ...also foam cracks @ 10% deflection, mineral board take 25%..so it can add to the COb composite flexure, compression, and shear strength better than the others you mentioned but it cost more up front. If you add the wood panels skins to mineral wool core all the mechanical strengths noted have improved especially if tied to a upper bond beam, corner and center post of the correct spans and size....again for large winds and earthquakes only not Wyoming persay.

 
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