Cob Appropriate For Home: Zone 6a, More Data in Post

Hello all! I need to borrow some brains. Anyone got one I can use for a moment?

I've read in SOOO many texts that cob isn't appropriate for areas with cold winters. And that's it. No description of what "cold" means. I suspect someone in Alaska finds 15 balmy while we'd be freezing.

So here's some data from my area. Heating is not a big concern - there's lots of timber on-site. But condensation is most definitely a concern since we'd be heating non-stop for at least 4 months.

The site location is not ideal: north side of a hill. I still don't have data on when the sun hits the site we're considering. But let's assume it's limited.

As a complete novice, the data coupled with the site location suggests that cob is not appropriate for this project - a 500 square foot home as primary residence.

- - - - - - - - - - - - -

Average Extreme Low: -5, -10
Sunny Days: 166 (Avg. 205)
Typical Cover: Overcast

Avg Lows:
Nov 33
Dec 23
Jan 17
Feb 20
March 28

Average Daily Temp:
Nov 42
Dec 31
Jan 26
Feb 28
Mar 37

In this case, "cold" means when the thermal mass of the cob becomes a negative, rather than a positive. To give a ridiculous example, building a cob house on top of some permafrost would not be a good idea. In that example, to keep the place livable, you would have to be continually heating all that cob and would get no benefit from the thermal mass, because there would be no time of the year that the cob could actually soak up and store some heat.

To really see if cob is appropriate, think instead about the time of the year that has the most pleasant temperatures. Is that March? May? July? The high thermal mass of cob will extend that pleasant time of the year, as it takes time to gain or lose heat to the environment. If it is pleasant in your area in a tent in April and October, then putting a massive cob structure around that tent is going to extend that time span to maybe March through May in the spring and September through November in the fall. You still have a few months when you need to heat, but not as many, and the same consideration about cooling in the summer.

If July is the only month when temperatures are halfway tolerable, and it freezes the other 11 months of the year, then if you build a house with a lot of thermal mass, you are going to be spending a lot of time heating that thermal mass.

You've read this, by Ziggy at Dancing Rabbit in Missouri?

http://www.small-scale.net/yearofmud/2011/03/03/cob-building-is-not-appropriate-for-this-cold-climate/

He built himself an uninsulated cob house (he's got a great writeup along and along), then changed his mind about it a made it a three-seasons guesthouse.

John,

I think I wanted the easy answer : yes or no. Your reply was much more thoughtful, informative, and ultimately helpful. It highlighted some problems with my thinking (I suspected I was quantifying a bit too much but oh we'll!)

Again, thanks so much. I appreciate it.
Brian

John Elliott wrote:In this case, "cold" means when the thermal mass of the cob becomes a negative, rather than a positive. To give a ridiculous example, building a cob house on top of some permafrost would not be a good idea. In that example, to keep the place livable, you would have to be continually heating all that cob and would get no benefit from the thermal mass, because there would be no time of the year that the cob could actually soak up and store some heat.

To really see if cob is appropriate, think instead about the time of the year that has the most pleasant temperatures. Is that March? May? July? The high thermal mass of cob will extend that pleasant time of the year, as it takes time to gain or lose heat to the environment. If it is pleasant in your area in a tent in April and October, then putting a massive cob structure around that tent is going to extend that time span to maybe March through May in the spring and September through November in the fall. You still have a few months when you need to heat, but not as many, and the same consideration about cooling in the summer.

If July is the only month when temperatures are halfway tolerable, and it freezes the other 11 months of the year, then if you build a house with a lot of thermal mass, you are going to be spending a lot of time heating that thermal mass.

Great info, Thank you for the post. I am thinking high mass as well and this post confirms for me it may work well for me. I could live outside for most of the year here. I was working outside in a t-shirt this week for example (working hard, I could not stand around without a coat). I will however, try to have a more insulative outer layer... that breaths. Cob homes have been used in the UK forever (almost) and the climate is very similar here.

Hello Brian, et al,

What I'm about to write could be taken as disagreement with John E., so to set the record straight, it is not. It is an "expansion," and broader view. You can build cob (or other thermal mass wall architecture anywhere-such as log, as one example) yet it is not the "what"-(cob) but the "how" (modality and species of earth architecture) that can "make" it work in colder climes and environs. John and I both have been trying to stress to folks for some time now, the "why" is the important question to ask. So many, outside of this proper "why," seem driven to use earth architecture in places they should not, and in a "species" type that would not be applicable.

You can find "earth architecture" in almost every cultural group on the planet from Athabascan cultures of the Arctic all the way across the globe. So YES you can use cob, but ask if you should, do you have the skill sets to use it properly, and is it the best choice for a region you are in compared to other vernacular architecture. Often I do not believe it is, as many just "want to have cob," when something else would be much better suited.

"Ziggy" (formerly of "Dancing Rabbit"-"the year in mud") is a friend of mine, and would (has) shared plenty on this subject of cob applicability.

Regards,

j

There is one place in the home where cob makes perfect sense in most cold climates. Build a rocket mass heater, then a cob wall near it, then some book shelves... Build a bread oven in the yard. All of these projects will allow you to work with cob, without comprising your ability to heat the home. Build your walls from materials suited to your location.

>So YES you can use cob, but ask if you should, do you have the skill sets to use it properly, and is it the best choice for a region you are in compared to other vernacular architecture.

That's definitely me (in my relative infancy learning about this topic). I am taken with cob's aesthetic and cost. I think our right angle housing world offends my sensibilities (whatever the hell that means).

That said, I'm also pragmatic. So if it doesn't make sense (we're getting a -10 night coming up in the next few days) then I won't do it, and aesthetics be damned!

My thinking has changed a bit to a hybrid design where there's bale on the outside, but with the straw oriented vertically (some research suggesting a higher R-value in this orientation) and then 8-10 inches of cob inside.

More work? Definitely. But this is going to be our home for 3 (or more) decades and there are many other buildings on the site so it mitigates the urgency to some degree.

Again, my thinking (and knowledge) is pretty sophomoric at this stage and largely idealistic. Luckily my research/pragmatic side brings me to you lot!

So thanks, you lot!
Brian

I'm with Dale on this one. You can use cob in the right places, even if your climate means that you shouldn't use it for the external building envelope.

Build a RMH (every time I type that out, I want to use "an," damn grammar intuition), or a partial mass enclosure on three or four sides of a cast-iron stove, or cob built-ins. Experiment with including thermal mass in the home.

Personally, I want to eventually experiment with a natural analog to insulated concrete forms. If you can thermally isolate the mass to be heated from the seasonally frozen mass of the earth, your only issue will be making sure you don't make the mass too hot.

As has also been mentioned, though, there are more considerations, too, than how hot and/or cold it gets.

-CK

You're right Brian, there isn't much info out there about cob and cold climates. So the only way we could get the info, is to find it through experience. We built a small cob building to see how it performed up here in Northern Ontario. We planned on temporarily living in it throughout the winter, but the building department wouldn't have it. So regrettably, I can't comment on it's performance of having a continuous heat source inside while the temperature is below freezing on the outside. We plan on building our home with cob, but not until we give this smaller version a go. We plan on visiting our cob building. When I say visiting, I mean staying there for a couple of weeks (not living), and getting the heat turned up.

The 'Why?' question is a good one. But I also ask myself, 'Why not?'. Up until stick-framing, log and stone houses was the norm in this area. Both utilize thermal mass, and they worked just fine. But they require a specialized skill in order to build them properly. I wouldn't call cobbing a specialized skill. There are oodles of reasons of 'why' we want to build with cob, but we can't find one 'why not'. Sure, a design utilizing insulation will provide an even steady temperature, but for us, we appreciate an ever-changing temp. So a question regarding heat falls into the 'why' category. But we can't jump to any conclusions, which is why we want to perform this test.

There are many things that can be designed into a cob building to 'help' take advantage of it's thermal mass, but it will no way, as far as I can tell up here in the North, be comparable to a building that utilizes insulation. If you're curious if a thermal mass building works in cold climates, try to find a log or stone cottage, and give it a whirl. There are some differences with cob, but in regards to thermal mass, not many. As far as condensation goes, a fire will pull moisture out of the air, and an open (cracked) window should help as well. I think condensation will happen, especially when cooking. But as long as any moisture that ends up in the cob has a chance to dry, say throughout the night, then all should be fine. We'll find out on our test run, and make note of it on the website.

Yes, there are many examples of homes with thermal mass TM walls instead of highly insulated walls in cold climates. Why not? Homes with properly installed insulation instead of TM for exterior walls will require orders of magnitude less energy to stay comfortable.

Hell Patricia, et al,

Patricia Ramirez wrote:You're right Brian, there isn't much info out there about cob and cold climates. So the only way we could get the info, is to find it through experience. We built a small cob building to see how it performed up here in Northern Ontario. We planned on temporarily living in it throughout the winter, but the building department wouldn't have it. So regrettably, I can't comment on it's performance of having a continuous heat source inside while the temperature is below freezing on the outside. We plan on building our home with cob, but not until we give this smaller version a go. We plan on visiting our cob building. When I say visiting, I mean staying there for a couple of weeks (not living), and getting the heat turned up.

Can't wait to get your report on that adventure. As for finding information you have to come at the topic sideways and not call it cob (or what type of cob?) and/or look at other mass wall insulation types and how they perform.

Patricia Ramirez wrote:The 'Why?' question is a good one. But I also ask myself, 'Why not?'.

I can give you a list of "why" you probably shouldn't or at least, not the way most folks are using cob. You can also seek out the people that would tell you "why not," and I have already referenced one of them on this post thread. It is not the who that is (cob) but the what, as in what kind, as some may work, some may not at all, and others could be fantastic-especially combined and working in concert with other vernacular forms.

Patricia Ramirez wrote:Up until stick-framing, log and stone houses was the norm in this area. Both utilize thermal mass, and they worked just fine.

Now I agree with you (kind of) as I use this example myself all the time when talking about the pro vs the cons of thermal mass in colder climates, yet the "just fine" part can be very subjective, and again, many (most) did not work fine by any comparable standard today. They could (and some did) but most did not, especially after the turn of the century.

Patricia Ramirez wrote:But they require a specialized skill in order to build them properly. I wouldn't call cobbing a specialized skill.

Hmm, I think perhaps you should rethink that one. Yes many folks are excited about cob (many are downright "nutty" about it) but that does not make it (when done properly and in good modality for the environment its in) easier that log or even stone. Having studied and done several forms of each tells me they are all about the same, just different, and since many of the log vernacular forms include cob, they are exactly the same.

Patricia Ramirez wrote:There are oodles of reasons of 'why' we want to build with cob, but we can't find one 'why not'.

Take this for what it is worth, but as a professional builder of natural styles, teacher and facilitator of same, when I meet folks that have drunk too much of the "CoolAid" on any style be it cob, log, timber frame, or you name it that they can not make a list of real pros and cons, worries me. You need to step back and be really critical of any system you are considering. If you have build (and lived in) lots of cob (or done extensive and exhaustive research of both pro and cons), then you have a good handle on its realities, if you haven't then you need to before putting all your eggs in that basket.

Patricia Ramirez wrote:...which is why we want to perform this test....

Excellent!!! you should (and then tell us all about it and what you think. )

Patricia Ramirez wrote:There are many things that can be designed into a cob building to 'help' take advantage of it's thermal mass, but it will no way, as far as I can tell up here in the North, be comparable to a building that utilizes insulation. If you're curious if a thermal mass building works in cold climates, try to find a log or stone cottage, and give it a whirl. There are some differences with cob, but in regards to thermal mass, not many. As far as condensation goes, a fire will pull moisture out of the air, and an open (cracked) window should help as well. I think condensation will happen, especially when cooking. But as long as any moisture that ends up in the cob has a chance to dry, say throughout the night, then all should be fine. We'll find out on our test run, and make note of it on the website.

Yes, high R factor insulation will outperform in thermal resistance, but not in thermal inertia, and if you combine the two systems you can achieve net zero architecture but the build will be costly in either money or time perhaps both.

Some quick notes on this section, log is very different than cob, and stone is way different than both of those, so no, there are actually many differences in how their thermal mass behaves, and with some modalities it can be extreme.

Condensation, depending on the skill of the builder, design of the cob architecture in question and site location/human dynamic, this can be a real issue, if not actual cause the structure to be abandon.

In the early days of settlement here in central Canada the homesteaders often used sod to make their homes. This would be similar in performance to cob and I think there is a real serious reason why the practice was abandoned. Simply out in the cold winter months the structures were a beast to keep comfortable. Often in the early days the people built whatever they knew how to build, not what works best in their climate. I would not use the people used to do something argument to justify doing it now.

What I personally think is the most important aspect to planning a home build is efficiency so like J said rather than try and adapt a system you like to the world around you consider what system is most efficient in your area and work from there.

Sean Rauch wrote:
What I personally think is the most important aspect to planning a home build is efficiency so like J said rather than try and adapt a system you like to the world around you consider what system is most efficient in your area and work from there.

I agree, but...The Grid. Because of "The Grid" all home building in recent years is based on one style of building, heating air. We have gotten very good at heating air and can do so efficiently. However there are some problems with this heating air deal. Yes we can super (Hyper?) insulate, and the required level has risen to heights that amaze me. The problem with heating air is sealing and airflow. We can build a very tight house, but can we then make it a home? For me to make it a home I have to open some windows to get some air. Hypersealed homes have to have air exchange by law, but because of the difficulty reheating the incoming air the builder will do the minimum number of air exchanges required by law. Yes heat exchangers can move some of the heat from the outgoing air to the incoming air, but:

- They are expensive.
- They require ducting (one can write a whole post on why ducting is bad)
a) ducting is expensive
b) ducting requires annual cleaning... generally by someone equipped to do so
c) ducting is a place for mold to collect.
d) ducting can be a passage way for vermin
e) moving air adds to the dust level in the air
f) ducting requires air movers and adds to the noise in the house
g) ducting takes up space (Len can't count beyond G, he is a musician )
- The minimum air exchange rate is ok for survival, healthy air exchange rates are much higher (4 to 8 times) So to be healthy one would have to take an already very expensive system and add a magnitude in cost, and in space taken up by ducting or noise made by moving air and the dust movement as well.
- add to that the cost of a heat pump.
a) up front cost is very high
b) more ducting and all its problems
c) part of built in obsolescence... means as soon as you pay for it you need a new one, yes they are built to fail.
- The house would depend on the grid.

I am sure I have listed only a very small part of all the problems looking at what is around you. We have the same thing with wood stoves, if one goes by what everyone is using and is happy with... we will buy a metal box and happily go through many cords of wood to stay warm even though people long ago learned that high mass masonry heaters will often heat the same home with less than a cord... metal boxen in real life situations (not a testing lab) are 10% heaters, masonry heaters are 75% plus in practical situations and can approach 90% if the user is willing to deal with something a bit finicky.

The same is true with high mass housing. properly built high mass housing can work better than hyper insulation.

To be sure, what we expect from our home and what the aboriginals expected from theirs is different. As an example, 100 miles or so east of here they used pit houses... dig a hole is the ground, put a roof over most of it (think 3 foot hole in the middle of the roof) and live in it. In colder places there would be a fire going in the middle, but in what is now Delta BC, they did not use a fire in them, yet that was where the old and young who needed warmer dwellings lived. The inside temperature would have been 50 to 60 F. Yet it was "warm" enough not to need a fire. There were no hot high mass storage to snuggle up against either.

So we want more. High mass housing can do that. however, that high mass housing does need some insulation on the outside of the mass. It also seems the mass needs to be very large in colder places.... 20 feet larger than the house foot print has been suggested, but I think in many cases less would work too. This has been done successfully using concrete and plastic insulation. The air temperature can be lower than 72F inside but because the mass temperature is about 70F, the occupants feel warm. The high mass houses that are successful have a high level of ventilation. this ventilation does not rely on high tech exchangers, but rather uses the high mass to preheat incoming air and uses the heat from out going air to help maintain the mass heat... though often it is warm enough to just open some windows.... something the hyper insulated house can't do without reheating that air (AKA loosing heating efficiency). The idea of high mass housing is to have a big enough mass that the system does not have to be efficient. It can be lossy and still work. Note, these systems are not designed for high water table, and permafrost locations may provide some interesting hurdles as well

The problem is how to adapt this to cob and other "built from found on the land" build systems. Most of these systems require the wall to breath for the health of both the wall and the inhabitants. Most insulating systems work by stopping all air flow. So using plastic insulation is problematic. A cob wall with a portland cement based stucco, will likely fail. WOFATI does this by covering the whole structure (almost) with an insulated berm. Can we do this with cob? Cob is some what insulating and could be insulating enough with less thickness than earth, but in the land of permits the wall would start using up a lot of that paid for permitted space... or make the maximum no permit required size to small to use This could be reduced by making the cob have a higher ration of organic matter such as straw. while this would make the wall less strong, having a thicker wall would make up for that. (the math would need to be done to find that right balance) I think the better path is to use cob for structure and mass and use an outside layer who's job it only insulating. I have heard straw bale suggested, but wonder if that would be too much on the mass side. The thickness needed may be too high. My thoughts (from the arm chair... so use a grain of salt) is to use a very high straw content cob... basically straw with clay slip. Then an earth plaster over that. Another idea is to borrow earth bag ideas and use bags of naturally insulating materials. The bags would not "have " to be stacked, they could be hung vertically. Net bags could be made of what is at hand (cedar bark in this area). This does sound like a lot of extra work, but the main thing is to have a good foundation and roof, the insulation can be added later.

One more thing with high mass houses.... they do take time to "charge up" the first winter or two will likely need more fuel to stay warm. I wonder how many failures have been because people have been impatient. I know of more than one person who have build a cob house lived in it through one winter and abandoned it. There are many others who are years down the road and happy.

Jay C., thanks for your comment.

I was misleading and my post was incomplete. With our plans to homestead, and with less-than-desired amount of money, we will most likely turn to utilizing locally harvested materials to build our home. With our combined skill sets and ideas on what our home needs to do for us, cob seems to be the best fit.

"working just fine" as I had broadly stated, is most definitely subjective. "worked" is probably a better fitting description. Thermal mass (log and stone) buildings were built over and over again for many reasons, including the fact that they worked. With the available materials and construction methods of that time, thermal mass buildings suited the needs of many folk. It just worked. And I am compelled to believe that they would even say it worked well, if not great!

I don't know if I used 'specialized skill' in the wrong context, but I think we can agree to disagree on this notion. When building our cob building I was more than happy to receive help from others to build the cob walls. Experienced or not, they could build the wall, the same way I would, with minimal instruction. I've never built a stone or log building, but I don't think an unexperienced person could do it properly. Cob is very forgiving in it's construction. I can't say the same for stone and log. True, there are a lot of things in cob buildings, as a whole, that do require a higher degree of skill and know-how, so I don't believe just anyone should build one. But building with cob, in itself, is pretty basic.

There are a lot of good thinkers out there trying to find different ways of dealing with the drawbacks of cob. Some of those ideas, I believe, are so different that I would no longer call it cob. My view is, there is nothing wrong with cob. To live in a cob house this far up north, I'm expecting to be uncomfortably cold. If being cold was unacceptable, then I simply wouldn't build with it, and would recommend that others do the same.

Like Brian H. had said, there just isn't any info regarding cob and cold weather. Overall, I'm pretty confident cob will work in cold climates, it's just a matter of it meeting each individuals specific wants and needs. Which is exactly why we are testing it out. Also, due to your (Jay C.) comment on condensation, I will definitely be watching for this more closely. I assumed it wouldn't be a huge issue, but if it concerns a man of your position, then I had better take note.

Thanks again Jay C.

I don't think anyone has commented on the location yet. Cob can definitly take advantage of the sunlight and you'll probably have to burn more wood to compensate for it, but I don't think the lack of sun is going to be your deciding factor. Going with an insulated home is your safest bet. There's loads of data and better control in regards to the interior environment of your house. But if there are factors that require you to use cob, then I say go ahead and use cob. Will it be warm and dry enough for your likeing? It's a risky bet, but currently there's really only one way to find out..., call yourself a pioneer and build it!

I've read cordwood does well in New York. It might be a viable option and may even get some solid data to start with.

Here's a website:
cordwoodmasonry dot com

Hello Patricia,

Please forgive me if this seems belaboring a point, but as a professional builder and teacher, and this being a public forum that lay folk read, I become concerned if an inaccurate impression is left.

You wrote: "...I don't know if I used 'specialized skill' in the wrong context, but I think we can agree to disagree on this notion. When building our cob building I was more than happy to receive help from others to build the cob walls. Experienced or not, they could build the wall, the same way I would, with minimal instruction. I've never built a stone or log building, but I don't think an unexperienced person could do it properly. Cob is very forgiving in it's construction. I can't say the same for stone and log. True, there are a lot of things in cob buildings, as a whole, that do require a higher degree of skill and know-how, so I don't believe just anyone should build one. But building with cob, in itself, is pretty basic..."

We can agree to disagree, but for the record, when I share views (apologies to all for sounding boorish) with someone that may have a "jaded love" of a building system, reads several books that support that view and then did one of two projects with it, now believes they can enter a lucid and comprehensive discussion about its pros and cons, and dynamics of a method really does a disservice to the realities in there entirety. One of my primary concerns as a professional builder is the concentrated number of "structural cob" buildings being built by lay folk with not structural engineering background, or even 5 to 10 years of experience building with this method. Yes it may seem "pretty basic," and in some regards, for smaller buildings I am sure it is and safe, yet that is not what most folks are going to try and do with it in there final project; they are going to build a house with it. Can they? Yes, by all means, but it is neither a "basic" skill, easy or as simple as many are making it out to be. This type of "laxity" and oversimplification can lead to catastrophe...and often does.

Regards,

j

Exactly!

Here is how I'm trying to work my head around things like cob. I am trying to find ways to incorporate cob into a building, make the most use of its properties without using it to a fault. So right now we are looking at ways to use cob for thermal mass inside the insulated envelope.

I understand the appeal of cob in that it can be free building materials but the hard truth is that there is no free lunch. In a cold climate like mine I wouldn't ever consider cob as a part of the structural system unless it is maybe used in conjunction with straw bale.

Building in the cold climates isn't anything like building in the warm. You can't just take an idea that works in the south, bring it here and expect good results. The pressures on a building are extreme in comparison to warm climates. When we build we need to start from a primary performance endstate goal and work back from there. I don't see how you can combine structural cob and those goals in a cold climate, sorry.

Good points Sean, and well understood. Cob as it is thought of by lay folk in North America, is not how it is was or is done (to good effect) in most cold climates. Can you just have a mass cob structure, of course, and there is even a video now on this section worth watching of a very massive home in the U.K. (not in its colder region per se) Even this build, done by a professional has some issues and by no means is a "sustainable or natural-traditional" example of using pure cob when you compare foot print, cost, support materials, etc used.

If I was helping someone in the an area like Winnipeg that had a good "clay layer" they could dig, and limited building experience, time (and/or some money accordingly) I would help them facilitate a simple timber frame super structure either with a "posted," stone plinth, and/or rubble and gravel trench foundation (or a mix there of) depending on skills and resources. This could be as complex or simple as they would choose, either with full fitted and traditional cut joints or the much more primitive yet simpler lashed together joints. The latter, if done with grace, can be very aesthetically pleasing with limited skills and resources, as well as fast. Then a "wattling" between the primary members, all lashed or "trunneled" to the super structure. Now the exterior walls could be straw bale between the support structure if there was fiscal resources to support that, or a number of other natural mediums from traditional "kubbhus" Swedish (or kubbe hus in Norwegian) to regional "Piece sur Piece" methods, and the list goes on. All which has to have a substantial insulative blanket covering the outside of the the structure (wall thickness a minimum of 300 mm and more like 500 mm plus) that should permeable to stay enduring.

That is the basic formula for anyone to follow in a colder climate.

regards,

j

For the OP

This year we had almost one straight month of below -30 consecutive highs with severe wind chills around -50. This is unusually cold but it does happen and if you're thinking that a thermal mass structure can flywheel through something like that you're in for a huge letdown. The thermal flywheel will stop and you'll likely be struggling to keep the interior surface of the walls above freezing. A relatively massive amount of heat energy will be expended as well as individual input just to keep it livable. The mass starts to work against you in a big way.

In the past settlers did it and many suffered horribly as a result. When your home is struggling just remain above freezing while the earth beneath your floor is frozen solid it's a whole new level of suck hahah.

I'm in zone 8b. We're close to the northern terminus of the Oregon cob craze. I've been inside about a dozen cob buildings. Three of them were built well. None had good thermal performance in my expert opinion. Even the well built ones pig through too much firewood. In this relatively mild climate, uninsulated cob has shown that it is out of place by probably 500 - 700 miles. Most structures are near sea level. The situation gets steadily worse at elevation. I'm in the warmest corner of Canada. Results in other areas of the county will be less favorable when interpreted by my criteria.

Apology accepted on both counts.

I'm confident that not one of my comments are lucid or comprehensive. And I'm sure that anyone who reads them can tell that a layman has written them. All the comments I post come from my personal experiences and ideas, as well as information I have gathered. It is through these concepts that I have found cob to be a basic skill. (I will stress that I, a layman, have found making cob to be a basic skill, in my opinion.) I read up on it, performed simple tests with different mixes until I found a satisfactory combination. I then decided on a method of mixing the ingredients that worked for me. The end result was a substance that I would call cob. The whole process it took to make my cob, I feel, is basic.

Now to use this cob structurally and effectively, in a building, I agree is not basic at all. And to be sure a building that is built with cob is sound and safe, I feel, can only be accomplished through engineering and a consistent cob-mix. To do otherwise is risky business.

I'm in awe at those who say building a house, of any kind, is simple and easy. Personally, I find house building to be very difficult and challenging.

But if others are like us, and willing to pioneer and explore cob and it's construction capabilities, I will not dissuade you, but only warn you to expect failures... minor and catastrophic.

This is totally personal belief... However, I don't believe in the theory that we can simply take what has been done in the past, like Cobb huts and apply it to the world around us. It's time to start thinking on a higher level and to me that's what JC and I have been arguing in this thread. Yes you can build to varying degrees in a more natural way but the real questions like JC said is, are we building sustainably? Are we building for long term efficiency? Are we building for human health? Are we building for long term quality? Sometimes Cobb works to accomplish this sometimes not.

We quite often get visitors who in Jay C's words "may have drunk a little too much cool-aid". If anyone is unsure of whether this has happened to them, Brian Knight offers regular reality checks to the self deluded. I recommend clicking on both fellow's names as a means of clearing up misconceptions of all sorts.

I mentioned earlier, that these houses pig a lot of firewood in my area. Good round poles are quite cheap around here, but some people are very keen to not "waste" any wood while constructing cob cottages. Most of them are located within a few miles of beaches that contain suitable logs that get burnt on the beach or water log and sink. (It seems to be the same crowd that worries about wasting water in our wet environment, as though it were forever leaving the hydrological cycle.)

The same people who are so averse to using wood in their walls, are willing to put several extra trees up the chimney every year for the entire life of the house. Quite a number of these cottages have been built without adequate care to the foundation and roof overhangs. That, along with an earthquake, could greatly reduce life expectancy.

What a great discussion.

I think we can confidently say that cob alone would be inadequate. So I've turned my thinking to hybrid designs: how would you "stick" interior cob to exterior straw bale?

If you could confidently link the two, then questions about load bearing abilities come to mind. And since I have a family I can't really move them into an experiment. Well, I could... but then they'd run away, write a book, and there'd be a documentary about dad's stupid house.

I'm not super pro or con anything so non-natural materials wouldn't be a deal breaker.

Maybe we need to have a 3 season cob home and a winter McMansion. Yeah... that'll do!

Brian Harris wrote:What a great discussion.

I think we can confidently say that cob alone would be inadequate. So I've turned my thinking to hybrid designs: how would you "stick" interior cob to exterior straw bale?

If you could confidently link the two, then questions about load bearing abilities come to mind. And since I have a family I can't really move them into an experiment. Well, I could... but then they'd run away, write a book, and there'd be a documentary about dad's stupid house.

I'm not super pro or con anything so non-natural materials wouldn't be a deal breaker.

Maybe we need to have a 3 season cob home and a winter McMansion. Yeah... that'll do!

The simple answer is structural straw bale with cob as the wall plaster. Its done all the time, no worries.

Sean Rauch wrote:

The simple answer is structural straw bale with cob as the wall plaster. Its done all the time, no worries.

How thick can this "cob as the wall plaster" be? Or is that the right question? how much does the straw act as mass and how much does it act as insulation? Or, in a high mass house, are the outside walls a significant percentage of the mass even if they are cob all the way through?

It's just typical Strawbale design. The straw walls already have a lot of mass.

I don't think you can make cob a sustainable primary building product in colder climates.

Hi Len, if you design correctly, the cob, cob lime or related parging and plastering can be as thick as you would like (100 to 200 mm is typical for "massing" on a SB, or related thermal layer to add the "energy sink" you are looking for. Of course this is done on the inside of the structure not the exterior. I would also suggest focusing on "internal" wall massing with cob or the related near the heat source for the home. You also can use clay straw, or clay chip/sawdust as your insulative layer instead of SB, as well. I recommend that the SB not be structural and you rely on some other structural modality like a timber frame.