How do you insulate cob or earth bag walls in the Northeast?
Hello everyone, I am brand new to this forum even though I have been spending the last three months here reading and enjoying the comments and articles.
My wife and I are looking to build a cob house / cottage. We live in western NY where winters are snowy and there is substantial moisture. After some extensive research we do not feel completely comfortable with straw bale and are leaning towards building with Cob for all the obvious reasons. 1. it will be cheap. 2. We have lots of clay. 3. It will last, no termites, fire resistant and we can be more creative etc…
We also like earth bag construction but is it as stable as cob and what happens if or when a bag breaks?
We keep hearing you should build a hybrid in the north east (straw bale north walls, cob south/ sun) but we just don’t feel that the structural integrity and longevity of straw is as good as cob (especially in an area where moisture can be a problem). Wouldn’t the straw eventually break down, especially if exposed to moisture during the build or over time? Also, having to frame and use rebar adds to the cost of our build. The only major issue we see with cob is the R value.
So our question is this: Can we build with cob and put foam board or spray foam type of insulation on the outside of the house or could we create two 6 inch walls of cob, one inside and one outside, with insulation (cellulose, foam board, whatever?) wedged in the middle?
I saw Kevin McCabe did this with his “cob citadel” What issues do we face with this?
We are environmentally conscious but will have to compromise as we have a very fixed budget and will need a realistic R value on the side walls.
Your ideas, opinions and experienced guidance would be helpful.
Take care and thank you for your time.
-Aaron
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Replies
Have you built anything out of cob or earth bags? If not, build a tool shed or dog house or something small and see if you can picture yourself building an entire house.
I'd be interested to find out what percentage of such structures are finished. My bet is less than 10%. The process looks easy, but tedious.
Keep in mind that the walls aren't the most expensive part of the house. If you want insulation, heat, plumbing, septic, windows, a roof, etc. you'll need something other than clay and straw.
Stephen,
Thank you for being condescending without answering our question, and yes we have both worked with cob/adobe before. Our specific question is how to insulate walls that are either cob or earth bag for northern climates and not if we have the ability, skillset or temperament for physical labor. We understand where the highest costs will be, that is why we will be doing the work ourselves and have narrowed down our building materials to either cob or potentially earth bag, and not straw bale or traditional post and beam construction.
-Aaron
Aaron
My apologies.
As a matter of (serious) interest, why did you choose cob over a more conventional method? Up here (just north of Maine) the climate is such that anything made of clay moves significantly as the seasons change. It would also seem that one would have to have very large overhangs to keep rain from the base of the walls. How does one handle window sealing (for example) in those circumstances? We do have the odd straw bale house here, but no cob that I am aware of, so this is all new to me.
Tony.
Aaron,
I'm not sure if I can contribute anything useful to your inquiries but I find your questions interesting.
I have almost no experience with the building techniques you're referring to but I have read a fair bit.
One thing I can say given the research I have done (which is probably limited and may not be entirely up to date) is that it is difficult to insulate those types of structures without getting away from traditional techniques.
For example, the so-called "SIREWall" rammed earth technique discussed in this thread:
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/23255/calling-all-rammed-earth-experts
Anyway, I'm curious to see what kind of help you get here with your questions.
Cheers.
Do all the labor and switch to double wall cellulose filled... Same cost, half the labor, much safer in this climate, Green...
As to cobb.... get with local cobbers is what I would do if cobbing. GBA is not a big player in the online cobb world.
And yes... let us know how you make out! Keep us posted
Maybe I'm thick skinned but I'm at a loss for how pointing out the realities of building with cobb is being condescending. Our area is littered with half -finished cobb structures built by well intentioned amateurs. Most of the completed ones are at the scale of sheds or cabins.
Malcolm,
I have a pretty thick skin too, but I think I get where Aaron was coming from.
Sometimes when you're on the fringe of something, you feel like people are constantly trying to get you to justify why you're there.
It can be tiresome.
Lucas, I'm sure you are right and I probably should apologize to Aaron too. Living here in Lotus Land where every second client wants to use an "alternate technique" has obviously made me more thin-skinned than I realize.
The last cob structure I visited was a barn at a local organic farm where I was bitten quite hard by a pig. Perhaps that plays into this too.
Malcolm,
+1 for humor.
plus 2
I think Stephen's question was reasonable and not condescending at all. If you're building in an area where cobb has no traditional presence and if I understand correctly no local skills in the medium to call upon for support it's quite appropriate to ask if the intended builder has the resources to carry it through. I have to wonder too if the fact that a region with several hundred years of settled history and an ample supply of clay has no cob tradition tells us something about its suitability to the local climate and terrain as a building medium. Our forefathers and foremothers were extremely resourceful and creative and for the most part not hardly wealthy enough to ignore a low cost building techniques well known in the old country if it could have brought them good functional shelter.
Incidentally, while cob may be unattractive to termites I can recall being kept awake by the scurrying of rats through tunnels they had carved in the walls of an old cob mill house where I was staying in southwest England.
Stephen,
No problem at all about the comment and thank you for the apology.
Malcom and Lucas, I concur with your observations and sense of humor. +3
Just so you all know my wife and I are not some visa card hippies (a term I came up with and have used for years) from the burbs trying to save the earth while stomping around in the mud with our friends... (frankly we will be doing this job on our own).
We both have extensive experience building and have just been doing research on alternative, dirt cheap, (pun not intended) methods and the only one that would be the cheapest (no money at all for the walls; as we have the clay, sand and straw) is cob.
And James, because generations of people used one method does not make it correct and or the smartest. I have owned and lived in many homes over the years with a wide range of issues. Nothing is perfect.
And I think I have read that same point made about the "scurrying rodents in cob walls" on this site before. I find it hard to believe if the walls are finished properly.
I have also heard those same sounds in my current post and beam home.
Our current house was built in 1910 and the cob house you were in was probably from 1610...
Ancient cob structures thousands on years old, still exist for many reasons and there are many houses popping up all over the place including in the north east made with cob. I am not here to dispute the validity of using cob vs. traditional methods. If I had the budget I would pay someone to build it whatever "it" is...
We just want to do the best bang for the buck/ cheapest cottage/ home and cob looks like that solution (as long as we can insulate it).
If not, then AJ's method might be the way to go although it won't be the same cost as we would have to spend money on the wood.
Hopefully someone on this site has an idea on how to insulate cob walls in the north east... until then thank you all for your comments and I guess I will be forced to look on one of those "crystal squeezing" sites...
Take care.
-a
Aaron,
Here is some information from a cob wall web site:
"Q: My husband and I are very excited about building a cob home for our family. We live in Edmonton, Alberta and the winters get quite cold. Is it even possible to have a heat efficient home in -35 C weather?
"A: In a very cold region such as yours, I would not recommend building a large living structure entirely out of cob. Cob has great thermal mass but poor insulation value."
That said, I imagine that it's possible to build a thick sandwich wall made of cob / rigid foam / cob. However, I can't imagine that this type of wall would be cost-effective. There are many cheaper ways to build a well-insulated wall.
I would suggest that you consider straw bale construction or double-stud walls insulated with cellulose. Good luck with your project.
Aaron you misquote me. I made no claims that traditional, time tested technologies are de facto the best (though there is some cogency to that line of thought). I suggested only (to paraphrase) that at least some of the early immigrants to the area would have been familiar with cob construction from the old country but they might have had good reason to learn other ways of making durable shelter for themselves and their families. Not all building technologies are suitable for all climates and environments.
Aaron: what sort of foundation are you planning? I know nothing about cob building. Would you use a conventional concrete foundation or a frost-protected slab or something else. I'd imagine that a double 6" wall with foam in the middle would require a total wall width of 18" or so, and you'd need the whole structure supported by the foundation.
1. We also like earth bag construction but is it as stable as cob and what happens if or when a bag breaks?
It can't be as stable as Cobb since the bond is broken by the bag. Good indication you used the wrong tensile strength bag. Repair it.
2. We keep hearing you should build a hybrid in the north east (straw bale north walls, cob south/ sun) but we just don't feel that the structural integrity and longevity of straw is as good as cob (especially in an area where moisture can be a problem). Wouldn't the straw eventually break down, especially if exposed to moisture during the build or over time? Also, having to frame and use rebar adds to the cost of our build. The only major issue we see with cob is the R value.
You should stop listening to whomever you are being educated by. Strawbale is stronger than COB. It’s ductile core provides a low modulus of elasticity, surpasses seismic codes, wind and hail, tornados, hurricanes, the stiff skins do an excellent job transferring compression and shear wall loads to the foundation and roof, if done right. Strawbale also has a much better ability to wick water than cob since it is aerated or tubular, evaporating. Let’s see the last visit I had of a strawbale home was in Alliance, NE built in the late 19th century and still stands today. There is a lot to know about detailing plaster and stucco to air seal and prevent moisture problems. Who said they had to have “framing and rebar”? Look at 2015 IRC, Appendix s, no rebar use wood for pinning, not frame if you follow code for load bearing walls.
Cobs r-value or thermal bridging is just one issue. Lot to know here too such as atterburg limits, compression, shear, and fracture strengths. The r-value is adjusted by straw content. You run a u-value test sample to determine it while your lab is getting you other critical design info the PE needs for code compliance. The state on NM has earth construction code that is a good design guide if you have no code. http://www.nmcpr.state.nm.us/nmregister/xii21/14.11.11NMAC.htm ...They write dirt or the book, know the most, have the builds, and history. Get some allowable loads to a PE code or not.
3. So our question is this: Can we build with cob and put foam board or spray foam type of insulation on the outside of the house or could we create two 6 inch walls of cob, one inside and one outside, with insulation (cellulose, foam board, whatever?) wedged in the middle?
You don’t have to use foam as a thermal break, strawcrete or hempcrete are good option and have an r-value of 2.5/inch. You can use it center core, or casted outer wrap, in conjunction with high levels of straw in cobb, straw-lime-clay plasters and/or stucco to get the required r-value and strengths. If you use high levels of straw, sub 3/4 limestone for lower amounts of sand to get the strength up.
If you do not know what you are doing both methods can turn into a complete disaster. It be best to test a small configuration over a year, or winter, unless you are a seasoned pro.
Good luck!
If you are going for low cost, it would seem that foam insulation would not be the first thing to consider--cellulose is much cheaper per R-value. So I like your proposal to do a double wall with cellulose between. I don't know anything about cob construction and how to make sure the walls are stable with two thinner walls. You might need some bracing between them, perhaps blocks of foam here and there.
The question would then be moisture management. I'd guess it would be fine with nothing special, although I think an Intello membrane on either side of the inner wall would make sure that you didn't have any moisture issues.
And if you get pigs, be sure to train them not to bite the visiting building scientists!
Charlie, Just to clarify: Knowing my character, for the rest of the tour my wife refused to let me near the pigs again, so I was unable to even things up, resulting in a continuing resentment agains the cob-dwelling residents.