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roundwood reciprocal roof + cob/strawbale walls: FOUNDATIONS???

 
Philippe Elskens
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I will build a building with a reciprocal roof structure with roundwood in central Portugal. Non-bearing walls will be out of cob on the South side and straw bale on the North side, and the floor will be earthen.
My question is this: How exactly do I construct the foundations for this building? I want to build as eco friendly as possible, so would like to avoid pouring concrete. Using urbanite/recycled concrete is definitely an option, but since our land is stuffed with so many rocks (fist-size and smaller), I would like to use these.
I will probably have a soil test done, but would like to avoid putting any 'strange' materials underground (such as plastic). So to facilitate draining I would fill a trench (how deep should I dig?) with rocks, make sure this trench goes downhill uniformly, and extend it to a couple of meters away from our house. So everything drains to here. Is this a good method? Should I line the trench with some kind of textile to avoid the spaces between the rocks getting stuffed (which would inhibit drainage). I've also read that a 'binder' (possibly cob) should go in between the rocks...? Should I pay attention to the size of the rocks? Should I just fill the trench with rocks, or neatly 'stack' them?
Also, the roundwood posts that support the roof will rot when put underground, right? I've read on Tony Wrench's website (thatroundhouse) that the 'new' method is placing the posts on 'pads'. What are these pads exactly? Can someone explain this process please? Should I still treat the (bottom of the) wood with something (creosite)?

Thank you very much for taking the time to helping me with these (probably very basic) questions!
 
Robert Alcock
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Hello Philippe

Personally I wouldn't use post-and-beam in conjunction with a cob wall. The cob and timber move and expand-contract differently, inevitably causing cracks. Cob is load-bearing on its own. As are straw bales, but again, they tend to move in a different way. Also straw bales require very rigorous protection from the weather in a damp climate like Portugal's (I believe -- we are in Cantabria, which is very damp.) Straw bales (well protected) with post and beam, or else cob on its own, are good options.

If you use posts, they should go on top of something that won't let water seep up through it. Like a tyre or two, full of rocks.

Foundations: For the stemwall (between ground and ~50cm above ground) I suggest you try tyres filled with rocks. The drainage trench doesn't need anything to line it and definitely no cob between the rocks, but a piece of geotextile or equivalent on top of the trench could help to stop it silting up. Just chuck the rocks in and tamp them down, the more space the better.

Good luck. See our website http://abrazohouse.org for more info...

best

Robert


 
Terry Ruth
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I will probably have a soil test done


This is your first step, nothing can be determined until I see it. PI(Plastic Index or shrink/swell) Sieve analysts or grain size, MC(Moisture Content) a Geo-Tech Report. Bearing and shear would be good. Taken at least two different locations and at different depths two below frost line, two above, in the perimeter of the building. Do you have an online portal over there like: http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm
 
Terry Ruth
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BTW: Once we understand your soil better it may improve the burn rate of your wood in case of fire which will lower your home owners insurance and save lifes. If your using combustible appliances or high load HVAC, utility fossil fuels, your whole concept of eco-frendly and saving the planet just went through the roof. More than compared to OPC production. I'd need to see the complete design. If you have not done the embodied energy math you may be out on a limb with your reasoning. I'm guessing you have not done that math and your best choice for a hybrid wall design is natural concrete if you know how to design it. Hybrid wall designs do not do well structurally. Monolithic mass of the same mechanical properties is a better choice. Recycled concrete can create point loads, not good structurally. You will need to look at the wall loads from roof loads and design the foundation according to them which creates a hybrid loaded foundation mess.
 
Terry Ruth
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People say I don't make sense to average builder. So to put it simple you have too many materials in contact with one another. In order to do that you need to have a deep understanding of the reactions to one another. Robert alluded to some of it but there is more that would need more definition to design properly. A local structures engineers reaction s/b
 
Philippe Elskens
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Robert Alcock wrote:Hello Philippe

Personally I wouldn't use post-and-beam in conjunction with a cob wall. The cob and timber move and expand-contract differently, inevitably causing cracks. Cob is load-bearing on its own. As are straw bales, but again, they tend to move in a different way. Also straw bales require very rigorous protection from the weather in a damp climate like Portugal's (I believe -- we are in Cantabria, which is very damp.) Straw bales (well protected) with post and beam, or else cob on its own, are good options.

If you use posts, they should go on top of something that won't let water seep up through it. Like a tyre or two, full of rocks.

Foundations: For the stemwall (between ground and ~50cm above ground) I suggest you try tyres filled with rocks. The drainage trench doesn't need anything to line it and definitely no cob between the rocks, but a piece of geotextile or equivalent on top of the trench could help to stop it silting up. Just chuck the rocks in and tamp them down, the more space the better.

Good luck. See our website http://abrazohouse.org for more info...

best

Robert




Hi Robert,

Thank you very much for your input! Yes, our regions seem to have a pretty similar climate, Robert, so I will probably drop the strawbales on your advice. I also understand the risks of hybrid structures better now.
The reason I decided on a roundwood structure is based on Tony Wrench's advice on http://www.thatroundhouse.info/reciframes.htm
But also because it seems practical to already have a roof to work and live under before you still have to build all of the walls. Would we really have such a risk of cracking when building like this? Let's say that we would opt for the roundwood structure, are there better ways of 'filling in' the walls?
Another issue I am concerned with is how much load cob can bear exactly? We want to have a living roof, which, dependent on what plants you want on them exactly, can weigh up to 250 kg/sq meter! We would build our house out of several smaller buildings (practical and financial reasons, but also because we like the feel of that). The smaller units would have a 6m diameter (with an area of 28 sq meters this brings the weight of the living roof up to 7 tons!). I do occasionally see pictures of similar constructions, but fear that very often these are build by people who just risk it without calculating the structural aspects. Not sure if I am comfortable doing that Also, ideally our largest structure would be 12m in diameter, with a huge corresponding living weight of 28 tons! Off course, there's possible adaptations to this 'ideal': scaling down the diameter, reducing the living weight by putting less soil and less 'demanding' plants on top, but still... this seems like a huge challenge!
So far, I have not yet found anyone who can give me exact numbers/formula's on how to calculate the parameters of a reciprocal roof for a given diameter and weight, or the weight-bearing capacity of a cob-wall...
And what in case of an earthquake...? Not that Portugal is the most sensitive region, but still... it happens (Lissabon 1755 8.5-9.0 Richter). I have the feeling that posts are more reliable... but this is not more than a feeling, so I'm definitely open to change my mind!!!
As for the foundations, I have a couple of questions:
-do you mean geotextile ON TOP of the trench?, or IN the trench, completely surrounding whatever is in it?
-a quick google search shows me that there are biologically degradable kinds (hennep, cocos,...). would these be adequate (probably more expensive)?
-I am very attracted to the idea of using tires, but read somewhere that harmful gases are released... NO IDEA if this is correct. Does anybody know this? You say that this go on top of the ground, so not in conjunction with a drainage trench? Or would you dig the trench at the periphery of the stem wall?

Thanks! I will check out your website as well!
 
Philippe Elskens
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Terry Ruth wrote:BTW: Once we understand your soil better it may improve the burn rate of your wood in case of fire which will lower your home owners insurance and save lifes. If your using combustible appliances or high load HVAC, utility fossil fuels, your whole concept of eco-frendly and saving the planet just went through the roof. More than compared to OPC production. I'd need to see the complete design. If you have not done the embodied energy math you may be out on a limb with your reasoning. I'm guessing you have not done that math and your best choice for a hybrid wall design is natural concrete if you know how to design it. Hybrid wall designs do not do well structurally. Monolithic mass of the same mechanical properties is a better choice. Recycled concrete can create point loads, not good structurally. You will need to look at the wall loads from roof loads and design the foundation according to them which creates a hybrid loaded foundation mess.


Thank you very much for your reply, Terry! I definitely appreciate the detailed explanation!
Thanks to you and Robert, I understand the risks of cob/strawbale hybrids. Do you agree with Robert that even a roundwood structure with cob walls will cause problems?
Indeed, I have not made a embodied energy calculation. Can I do this myself, and how? Is an approximate calculation adequate, or should this be rather precise? Pff, there seems to be such a huge discrepancy between the technical answers I often get at this forum and the impression many builders give me in their youtube videos on how they build (as we would say in Dutch: 'with the wet finger', meaning they just build something and just hope it will be good enough):-s

I will definitely request a soil test and base my further plans on that! How expensive should I expect this to be more or less?

I would like your feedback on this one:
Our plan is to start building a small round structure as fast as possible, so we have a place to live in. After that, we can adequately plan and build the next structure. Eventually, this first structure will become a shed when we move into the second one. So long-term durability is of less crucial importance here. However, I am wondering whether it is realistic to assume we could live in it for a while (very difficult to estimate how long off course, but for the sake of the discussion let's say a year...)
 
Robert Alcock
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Hello Philippe

A lot of questions there.

First up. You will need some form of quick shelter in order to start building and living on your land. We had a grotty caravan but in an ideal world (with more money and experience, that is) I'd have started with either a wooden kit house, a yurt, or else a quickly put up straw bale structure with tyre stemwall. You could put this up in a couple of weekends, and if it's only meant to last a few years, don't need to worry too much about detailing. Once you have a base, you can start doing things properly. Really there's no point in messing around an trying to do something quickly that is best done slowly and carefully!

Tyres are pretty inert, I think they will only release significant amounts of chemicals if exposed to strong sunlight.

We have living roofs on our houses, but we don't use soil as a growing medium up there -- instead we use a mix of compost and expanded clay (arlita) which is a lot lighter.

Cob is structurally a very strong material because it's monolithic with no internal lines of weakness. It's also supposed to be earthquake resistant, I believe. You may have better luck asking these questions on the coblist http://www.deatech.com/mailman/listinfo/coblist

I recommend you read "The Hand Sculpted House". Most of your questions will be answered in there!

Good luck

Robert

 
Terry Ruth
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Do you agree with Robert that even a roundwood structure with cob walls will cause problems?
No not I do necessary agree without seeing a soil test and plan. I suggest you post them before taking any more advice. COB can have issues both internal and external, depending on compression and shear values and other physical properties. Due to the ductile core strawbale would be a much better choice in seismic events. In general take advice on how to build from builders, take advice on how to design from Engineers. $3-500 covers soil test here, money well spent. Then you need someone that can interpret the data and design accordingly. Another good thing to do after that is a build your temp structure out of what the main home will be. Before any building cut some core samples out of a test wall and take them back to the lab to get compression and shear. Use those values to design to your loads. Do not guess and use a safety factor of 2 in the design

I would not trust tires or any petro-based products or anything I could not find design load capability for by a test organization. Besides, the properties can vary in a foundation which is last place to have changing properties. Don't get to hung up on not using monolithic concrete your local ready mix should have tested for consistent properties, there are natural ones and sometimes they make the most sense. In most cases the OPC content is only 10-12% and that can be lowerd by an Engineer. There are other much higher C02 ways to pollute our atmosphere like truck shipping materials or using fossil fuels in your design. EE is a science not guess work and there are many myths regarding concrete.

Please do not misunderstand my last post, hybrid designs can work just need more info.
 
Robert Alcock
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Philippe,

As regards tyres, there's zero embodied energy involved since they're a recycled waste product. You're doing the earth a favour by keeping them out of landfill. And they are way strong enough to hold in the stones which are actually doing the job of holding up your house.

I think here we have two opposing philosophies in a nutshell. Either you use natural / recycled building materials and trust your own feelings and the accumulated wisdom of centuries, even if the engineers freak out because they haven't been trained in this type of building, or you go with industrial materials and professionals who will use their hundred-thousand-dollar educations to prove that black is white and concrete is the most efficient and environmentally friendly material. I'm pretty sure from your original post that you already know which way you will go, though...

Good luck with it,

Robert
 
Philippe Elskens
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An idea that just jumped in my head I decided to just post without really thinking about it:

Why not avoid cracks in cob walls, caused by differing properties between cob and wood, by making sure the cob walls are build around the posts, rather than incorporating them...
 
leila hamaya
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building something small and experimental before building your main house, is a really great idea. gets you out there doing it and learning, you can then approach the larger project with more hands on knowledge.

as for thinking about cob or straw bale, there is an additional option, which lends itself better to post and beam.
you might be interested to check out light clay straw --->

which is meant to be used with posts and beams, another words, non load bearing.
a related idea is slipform masonry, its similar.... only stone and concrete are used instead of the straw and clay slip.

Also, the roundwood posts that support the roof will rot when put underground, right? I've read on Tony Wrench's website (thatroundhouse) that the 'new' method is placing the posts on 'pads'. What are these pads exactly? Can someone explain this process please? Should I still treat the (bottom of the) wood with something (creosite)?


yes wood will rot if you try to bury the wood, or put it underground. there are some people who are even into the idea of building with wood deep underground, covering it with plastic, burning it, using treated wood, etc...IMO - which anyone is obviously free to disagree with - all bad ideas. the wood should not have any contact with the ground, or anything that would cause moisture to be absorbed by the wood.

i think the 'pads' that are being talked about are concrete, cement of some kind...as thats what many people do to raise the posts from the ground.
you can buy posts that are already attached to concrete pads on the bottom. there is a metal piece that goes between the bottom of the wood and the concrete, that is firmly attached and supporting the wood.
there is thread on here about using stone bases for wood posts, its pretty tricky though, attaching the posts to solid stone.

here we at least have some interesting options of *sort of concrete*...is the best way i can say it. there are companies that make these ...faswall blocks, and many other *sort of concrete* options for foundations, like using styrocrete blocks, either making them yourself out of free recycled styrofoam or for purchase. i have never used anything like this, but i think they are interesting options for the foundation, or anything below grade. they are at least easy to put together and understand how to do it, with dry stacking the blocks and then adding rebar and pouring concrete between them.

you are maybe looking for something like this...though ---> http://www.naturalbuildingblog.com/earthbag-foundations/
or ---> http://www.themudhome.com/gravel-foundations.html
or similar to ---> http://www.earthbagbuilding.com/projects/bwbhaiti.htm


and for the drainage issues, yes that sounds good, but you should consider the slopes around the structures, if any. you want to whole area around the structure to be shaped to shed water away from it. for instance if the earth is slightly raised around the perimeter, the water wont jump up that incline, even if its very subtle, but will follow the path of least resistance....which you should direct away from the structure. there is probably a clearer way to say that, but hopefully you get my point. a huge trench wont help enough if you are ...say at the bottom of a hill...so the whole area should be shaped as such that water moves away from the whole perimeter.
 
Terry Ruth
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..faswall blocks, and many other *sort of concrete*


Faswall and Durisol contradicts alot of what has been written on this thread. That is a wood chip, clay, magnesium chloride product. The mag chloride and clay binders have 100% petrified the wood & sand aggregates and the small amount of portland cement gives it additional strength. It is engineered by a proprietary process similar to nature, very difficult to duplicate unless you are a chemist. It has proven itself as an excellent healthy wood based foundation for centuries or since wood became petrified. I suggest learning more about these product types and natural concretes. They also make excellent walls and roofs.
 
leila hamaya
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Terry Ruth wrote:
..faswall blocks, and many other *sort of concrete*


Faswall and Durisol contradicts alot of what has been written on this thread. That is a wood chip, clay, magnesium chloride product. The mag chloride and clay binders have 100% petrified the wood & sand aggregates and the small amount of portland cement gives it additional strength. It is engineered by a proprietary process similar to nature, very difficult to duplicate unless you are a chemist. It has proven itself as an excellent healthy wood based foundation for centuries or since wood became petrified. I suggest learning more about these product types and natural concretes. They also make excellent walls and roofs.


yes, apologies to the op, i got a bit sidetracked there.
its just that i have known alternative type builders to be using and interested in those, considering them a greener option. thanks for explaining that, i actually didnt get how exactly that would work.

as far as things people use i have less issue with cement than with plastics, i am not too fond of the tires personally, and the manufacturing of lime is likely no better....and in this, the crucial part of the foundation something must be used. in my limited understanding these blocks, and the eps, styrocrete blocks, the other *sort of concrete* options are also insulation and water barriers...and i think they could be the right options for someone anyway......

as for everything thats out there, i am most interested in slipform stone work, or stones and mortar, now if only i could make a concrete without cement ! or other industrial weirdness.
i think a good foundation would be two layers of slipform stone stem walls, with an insulation layer in between them.

i have done a lot with soil cement, or something that is sometimes called stabilized earth.
a long while ago when i was doing more earth building, i made a couple of floors that way. no plastic, no insulation or anything other than subsoil, clay, gravel, sand and a bit of cement. a short ring of rocks around the perimeter, and some rocks that were embedded into the floor... then over that a (subsoil) earth/clay/sand/pigment floor. that was sufficient for glamping in for quite a long time =) but i live in a warm place.
 
Terry Ruth
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Leila, you got the right idea. My point was wood and clay can be combined with the right types and minerals/elements. There is alot of info on my "Breathable Walls" thread using Durisol or Faswall as ICFs, also Strawbale, Earth Materials, etc.....It would be like comparing apples and oranges to foam family ICFs that are vapor barriers since Durisol and Faswall have high perm ratings and sorption rates not zero like foam and plastic, but they require an exterior high perm parge coat when mated to certain soils to stop liquid water, or dimpled mats work good. Stabilizing soil to change it's properties is done by the better earth and geo-techs so they are more compatible with wood, for example, or one another. Most get lab test as I described unless of course there is a similar build to follow on the same soil, not likely.

Insulation-concrete-insulation or ICF is a bad design that keeps concrete from drying or vapor breathable. Concrete-insulation-Concrete is better since now we can modify the boundary layer of each concrete to adopt to different environments/mating, and we have a center core thermal break how much depends on temperature differences. ....The same extends to walls, foundations, roofs. Studies have shown 2 -4" exterior concrete (R-6-12 insulation core @ 2-3/inch) 2-4" interior concrete...convert that to meters I'm too lazy. Again, same applies to foundations. I like mineral wool board as floor or slab insulation since it has 700-1300 PSI compression @ 25% deflection....Foam is only a fraction of that...If higher is needed I go to a product called FOAMGLASS not cheap.

Tires are risky....I'd like to see one that is inert or a mfg claims that? There is a good chance they have an outgasing component especially when in contact with ground chemicals, breakdown and erode, they are a petro-chem rubber, like plastic a food for microbial growth and not chemically stable. As a barrier they will not allow drying or capillary drainage if water gets trapped in the tire. They will have different compression strengths so wall buckling in shear can occur. If they have a proven history there should be a design guide like concrete has. I doubt anytime soon we start recycling them into the bulk of foundations across the globe, and for a good reason, or we would have by now. Be cautious when people say they have proven by history without posting proof. There is rarely or no building technique out there without failures.

I grew up in CA, totally different environment than the rest of the country, we should have made a country out of it and the building codes there are nuts!

As far as cements search for "geopolymer cements" ...I agree why lime production is thought to more carbon negative than OPC without looking at quantity and shipping and just the 800-1000F lower kiln temp makes no sense. .
 
Philippe Elskens
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Ok, lots of new techniques=lots of research to do:p

I'm trying to mentally compare tires vs earthbags as foundations? What are the differences? Also, what do you use to fill them and why? I've read stones in tires, but earth in earthbags? Why not earth in tires for example?
 
Robert Alcock
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Terry: "They will have different compression strengths so wall buckling in shear can occur"
A tyre full of rocks is not working in compression. The rocks are holding up the building. The tyre is just holding in the rocks.
The fact that tyres hang around in the environment for decades without siginificant change is pretty good evidence that they are close to inert.

Philippe: "I've read stones in tires, but earth in earthbags? Why not earth in tires for example?"
The advantage of rocks over earth is that the water won't seep up through them as with earth.
You can do rammed earth in tyres, it's a method often associated with the Earthship design. But it's extremely labour intensive. Much easier to fill the tyre with rocks which don't have to be rammed in.
On the other hand an earthbag filled with rocks would probably be punctured by the rocks if they were at all sharp.
Having said that, I've not worked with earthbags.
 
Robert Alcock
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Well Terry, typing "tire foundations" into a search engine you'll find that there are quite a few examples.

Here's one from the UK's Strawworks which shows the technical details of a car tyre-and-gravel foundation for a straw bale building up to UK code. Note the load of the building is borne on A FEW car tyres rammed with gravel, not a continuous row of them, which obviously would spread the load much better. So, yes, there are examples.

http://strawworks.co.uk/wp-content/uploads/2013/02/SD-Car-tyre-pillars-130226-05-29.pdf

Many people doing low impact building don't want to go through the often huge expense of bringing their buildings up to code, which is why there are probably not so many examples as well documented as this. Just because you haven't studied something in engineering school doesn't mean it doesn't work.

By the way, as we're speaking of natural materials and reliability, here's a photo of a cob-walled house in Devon, the oldest known, dated to 1262. There are thousands of other medieval cob houses in the region. I don't think they had soil testing or engineering in those days, but they somehow managed to build houses that have been in continuous use for hundreds of years. Makes you think...
NWA_Townsend_view.jpg
[Thumbnail for NWA_Townsend_view.jpg]
Cob house in Stockland, Devon, dated to 1262
 
leila hamaya
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i strongly believe that a person doesnt have to be an engineer or professional builder to create their own shelter.
i think, its not rocket science! there are some important things to pay attention to, but they arent all that difficult to explain and learn.

i also strongly believe that a person can build a house for exactly as much money as they have, even if its very little.

yes it may have varying degrees of beauty, charm, as well as structural integrity based on their skill level, willingness to learn and carefully plan, thin or fat wallet....but i think it is something that is ingrained within us to create...as naturally as any other animal.

my experiences, as others here, are more of building on a tiny shoestring budget
a different wave, than the professional building world, thats for sure.

recycling everything you can, trying to do the best you can in regard to responsible material choices, and working collaboratively with non professional builders. where people of varying skills come together and learn and share and get better and better at figuring it out. i would like to honor my own and others experiences like this, and not see that discredited or undervalued.

 
Glenn Herbert
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"A tyre full of rocks is not working in compression."

I believe this statement is referring to the fact that a tire which is filled with rocks in a foundation/wall situation will be acting in tension to contain the rocks, while the rocks and to some extent the thickness of the tire sidewalls will be acting in compression to support the loads from above.
 
Robert Alcock
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Hi Glenn

Yes, that's basically what I was getting at. Thanks for clarifying. Except that since rocks do not flow, the tyre will not have to support the whole weight of the building in tension, either. If it was a tyre full of (say) very wet sand, it would be a different story...

Robert
 
I agree. Here's the link: http://richsoil.com/cards
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