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Strawbale in the Pacific Northwest, anyone?

Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
We're planning to build a home on our property (we're in an ancient mobile right now) and originally I was going to go with Cob, but I'm concerned about it's low insulative properties. I didn't think strawbale was an option since our climate is quite wet (i.e. high humidity in winter). Then I read a blog for strawbale building that claims it's not an issue. There are many cob houses around here but I don't know of any completely strawbale ones offhand (I heard of one person who put strawbale on the north wall, see below).

Here's my technical question: strawbale (and cob) allow water vapour to pass through the walls. The idea is that in winter, when people tend to be staying indoors alot and interior moisture content is high, the water vapour migrates outside through the walls because it's presumed that when it's cold outside it is not also humid. However, in our region we have mild wet winters and humidity can be high, so what happens when you have high humidity on both sides of the wall? Not a problem with cob, but with strawbale if the moisture doesn't migrate through the wall (because it's roughly equal on both sides) then it can sit in the wall and that is not a Good Thing when you have straw in there.

One person I spoke to last year (local) said they used strawbale on their north facing walls but put 4 inches of cob on either side (interior wall and exterior wall) to address this concern. I'm trying to figure out the mechanism by which this helps reduce the problem I mentioned above.


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Greg Hickey


Joined: Dec 24, 2011
Posts: 21
Mariah,

I think there may be some misunderstanding on cob, here. Cob walls have (depending on thickness) around a R-30 value. That is NOT low insulative quality. Strawbale does have a greater R value due to the additional depth of the bale. However it is not load bearing and thus only an infill that needs a rigid frame structure in addition to the straw. Both are good choices for the northwest. Are you on the west or east side of the mountains?

As far a humidity, both breath. True. Both need to be protected from the rain/wind. Expanded eves usually does the job. Cob does not saturate with humidity due to the density of the dried earth. Strawbale does not absorb a lot of moisture due to the compressive pressure of the bale. Straw must be baled, by the farmer, at around a 1000psi. That is very very tight. But is keeps moisture from gaining access to the interior of the bale and molding.

Both do need a good exterior coating to combat the moisture in the NW. Most people use a plaster on either construction. You will find that even in high humidity winters the walls will allow some migration inward, but not much. The real danger is sealing the wall and not letting it breath outward when it can. Then you will get an unhealthy structure, mold, and eventually interior structural damage.
Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
Thanks for your reply, Greg.

The information I got about cob is from the book "Building Green" by Clark Snell and Tim Callahan. The authors claim that opinions as to the true R-value of cob vary, possibly due to the fact that it depends on many variables such as thickness of the wall, straw content, etc. But they basically said that they wouldn't trust it. There are a few cob homes in my area and I plan to ask the owners how they are holding up, insulation-wise.

We do plan to use natural plasters, etc to seal the walls as per standard design. And yes, we will be using timber frame for the skeleton and the strawbales (or cob) will be infill rather than load-supporting.

Your answer about the moisture puzzled me, however. I'm not talking about rain (liquid moisture) but water vapour. I believe that straw bales allow water vapour to pass through (which is why they advocate not putting metal - rebar for example - inside or alongside the bales because the colder temp of the metal tends to cause the vapour passing through the bales to condense on the metal and now you have liquid moisture in the bale). And I believe this vapour passes through the wall by going down concentration gradients (from high to low concentration). So my question was: what happens when that gradient is very shallow.

Your point about cob may answer my last question: are you saying that cob holds a lot more moisture such that putting a few inches on either side of the strawbale would tend to prevent any moisture getting in the bale? But then wouldn't that defeat the point of natural building (which is to allow moisture exchange between indoors and outdoors)?

Thanks for your patience.

Greg Hickey


Joined: Dec 24, 2011
Posts: 21
You are in a great location for learning about cob. I am sure you are aware of the activities on Mayne Island. Take a short hop and see cob in action. http://www.cobworks.com/ That will tell you more than anything what cob will do in your weather/climate.

As far as my understanding of strawbale (admittedly my data is old. I gave up on the idea of strawbale about 8 years ago.) is that the very high compression of the straw keeps moisture in the form of vapor from migrating too deeply into the bale.

Realizing that my information was old I did some reading. It seems maximum breathability is the recommendation.

http://www.thelaststraw.org/bonus-articles/strawter.htm

There are no historical precedents of bales being used with moisture barriers, and consequently there is no data on how the two perform together. Most historical data for unwrapped bale walls demonstrates the importance of walls of maximum breathability: a mansion in Huntsville, Alabama, has successfully endured Southern humidity since 1938; a 1978 building near Rockport, Washington, receives up to 75 inches of rain a year; and an unplastered building near Tonasket, Washington, with no foundation and unplastered walls shows no apparent deterioration of the bales since 1984. Recent bale structures in northern New York (humid winters) and Nova Scotia (cold humid winters) have been monitored and demonstrate good performance in these difficult climates.

To better clarify my point on moisture with cob:

From: http://www.barefootbuilder.com/faq.html

Cob is a form of earthen building developed in the British Isles, a very wet area famous for beautiful mists and vicious storms. Yet the native cob buildings in these places have withstood centuries of harsh weather and still remain in use today. When I built a cob studio Pensacola, Florida in 2002 many people were skeptical that it would survive our 98% humidity and frequent hurricanes. However, the building has had no problems despite soaking rains throughout the building process and a hurricane that destroyed many of the surrounding wooden buildings. Even in humid climates cob does not rot, grow mold, get eaten by termites, or melt on the rain.

Cob is very porous and can absorb a tremendous amount of water without softening. In fact, unless it is completely submerged, cob will never just “melt”. It will however erode over time if it is exposed to direct rain. The solution to protecting cob from moisture is “a good hat and boots”. In other words, a cob house needs a good roof with wide eves and the bottom of a cob wall must sit on a non-absorbent stem wall so that it cannot wick moisture up from the ground or be splashed by water coming off of the roof. Cob walls are very thick, often two feet or more, so even the heaviest rain will never soak through more than the outer layers of plaster. Even if your walls get soaked with rain occasionally (like in a really big storm) they will be fine as long as they can dry back out. For this reason it is very import to never plaster a cob wall with a non-breathable coating like cement stucco.

As to your question on gradient, I am going to say that when the humidity is the highest on the Island, Winter, the structure will be heated from the inside creating a high or steep gradient (migrating outward.) The time of year when the gradient would be shallow would be the warmer months when humidity is at its low point. I am confused by your statement that "in the winter ... interior moisture content is high." From a relative humidity perspective, the air is less humid inside than outside presuming there is some heat differential to the outdoors. The warmer it is the lower the relative humidity. So the air inside the walls should be less humid by volume than the air outside. Am I wrong here? If so I apologize.

If in fact the inside is less humid than outdoors the air density gradient will be from low humidity to high humidity, even though it seems counter intuitive. http://www.usatoday.com/weather/wdensity.htm

Humidity and air density

Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air. How can the air become lighter if we add water vapor to it?

Scientists have known this for a long time. The first was Isaac Newton, who stated that humid air is less dense than dry air in 1717 in his book, Optics. But, other scientists didn't generally understand this until later in that century.

To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian physicist Amadeo Avogadro discovered in the early 1800s. In simple terms, he found that a fixed volume of gas, say one cubic meter, at the same temperature and pressure, would always have the same number of molecules no matter what gas is in the container. Most beginning chemistry books explain how this works.

Imagine a cubic foot of perfectly dry air. It contains about 78% nitrogen molecules, which each have a molecular weight of 28 (2 atoms with atomic weight 14) . Another 21% of the air is oxygen, with each molecule having a molecular weight of 32 (2 stoms with atomic weight 16). The final one percent is a mixture of other gases, which we won't worry about.

Molecules are free to move in and out of our cubic foot of air. What Avogadro discovered leads us to conclude that if we added water vapor molecules to our cubic foot of air, some of the nitrogen and oxygen molecules would leave — remember, the total number of molecules in our cubic foot of air stays the same.

The water molecules, which replace nitrogen or oxygen, have a molecular weight of 18. (One oxygen atom with atomic weight of 16, and two hydrogen atoms each with atomic weight of 1). This is lighter than both nitrogen and oxygen. In other words, replacing nitrogen and oxygen with water vapor decreases the weight of the air in the cubic foot; that is, it's density decreases.

Wait a minute, you might say, "I know water's heavier than air." True, liquid water is heavier, or more dense, than air. But, the water that makes the air humid isn't liquid. It's water vapor, which is a gas that is lighter than nitrogen or oxygen. (Related: Understanding water in the atmosphere).

Since heat will convect from hot to cold and air density will flow from high (less humid) to low (humid) the gradient should be the highest when the temperature differential is highest in the wet winter months, even when their is high humidity outside as is the case in the Pacific Northwest.
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
What is your timeframe? I'm building just south of Nanaino and will be using cob with plenty of wood waste in it. You are welcome to check on my results. Cob hasn't been tested in a big quake. Mine will be infill with a sturdy post and beam frame. I'm setting myself up with several machines to expidite the process (power mixers, tractor, rototiller plaster machine...). My crane is currently growing moss near your place and is available to anyone who will maintain it. All of my machines will eventually be available for rent and I may produce cob for a per ton rate.

My brother is currently unloading lots of building materials in Mill Bay. Good recycled fir.


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Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
Greg, thanks for all the great info. I have perused the cobworks website. I have visited cob structures here at the O.U.R. Ecovillage in Shawnigan Lake. One building there was financed by a credit union as part of a research experiment - there are sensors implanted in the walls to monitor function. I also know of two families here who have built cob homes. It was the Ecovillage folks who told me about putting extra cob on either side of the strawbale walls, but I didn't get around to hearing exactly how that works. We're lucky to have architects and builders here who are experienced with cob.

The issue with interior moisture is this: when people are indoors all day doing winter-y things (like making soup!) they build up a lot of moisture through breathing, water simmering on a stove, boiling kettles for tea, using the clothes dryer, or even hanging clothes indoors to dry, etc. Indoor humidity can be considerable and increases with the number of occupants per square foot of indoor space. In summer supposedly you aren't indoors much and/or you have windows open. Now, with that said, most people I know have wood stoves and these tend to do a good job of drying out the air indoors. We plan to have one in our new home so perhaps it won't be an issue. Just reading about how moisture builds up indoors with occupation by living things made me wonder if having high humidity outside while building up humidity inside would be an issue. At the Ecovillage the only all-strawbale structure I saw was a shed - not heated and no people hanging out inside. That also made me think about this issue. I plan to ask them some time.

My understanding when building with cob and strawbale is that, unlike any other type of home, you do NOT want to have any moisture barriers (like vapour wrap) as this is counter to the point of breathable walls. Since I don't believe there is such a thing as blocking out every bit of moisture (can't fight Mother Nature and all that), it's particularly bad if your wall interiors are made of stuff that reacts badly to being wet.


Dale, very cool that you are building nearby. I believe when the cob is mixed by machine (typically bobcats) they call it "Bob Cob". We would definitely use that technique since it saves hours and even days of labour. You say you will be using wood waste in your cob - do you mean using wood chips instead of straw for the cob mix? Sounds interesting. We are in Duncan, very close to Mill Bay.

We are hoping to start building in 2013. This year we hope to start the process, hiring the architect, doing the engineering work on the site, etc. We also want to incorporate rainwater harvesting and greywater treatment so many ducks must be in a row before we start building. The deciding factor is, of course, money. So if there is a change in the financial situation this year it could mean shelving the plans. Right now we are on track so fingers are crossed!

As for earthquake performance, there was research done here showing that cob is highly resistant to earthquake damage. I believe the researchers, using a scale model of a cob building that was actually built in Stanley Park in Vancouver (as a popcorn stand), is that it took up to 9 on the Richter scale before the structure began to show serious signs of structural damage. Not sure about straw bale but my guess is it would work pretty well. Of course, these were load-bearing walls they tested and if one uses timber frame I suspect the performance of that will be a critical factor.

It may be that cob is sufficiently insulative that it won't be a problem. Still, I wonder why people here tend to not use it on the north-facing walls. I like the look of strawbale because I'm partial to square and linear shapes, rather than the curvy sculptured look in most cob homes I see.
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Chris Magwood wrote a book called Straw Bale Building. It's the best reference I've seen for straw bale in cold and damp situations.

The waste wood will be mostly saw mill waste including saw dust, short cutoffs , and chips. It is for insulation. Some straw may go into it. Our straw is expensive and low grade. May need to import from Alberta.

I have no faith in cob's ability to withstand quake. Saw the video.

Un-insulated cob makes no sense for me, especially when the insulation material is free and it will reduce labour input since less cob needs to go in and everything will be lighter and faster drying.

Test blocks containing wood waste dried much faster than pure cob. The wood wicks moisture to the surface.

RMH going in as soon as roof is finished so that it can dry things out. It will also be used for cooking, water heating and possibly for electrical generation.
Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
Dale, do you mean the insulation (wood waste) is sandwiched in-between two walls of cob? Very interesting!

And thanks for the book reference!
pahanna barineau


Joined: Oct 03, 2010
Posts: 47
i lived 4 years in a 14 foot diameter cob dome with vapor barrior onthe exterior , with plenty of cooking going on and found it to not be a problem, of course the exterior was covered in dirt to protect the plastic so that the sun could not pull moisture to it, but the jury is still out at this time
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Mariah Wallener wrote:Dale, do you mean the insulation (wood waste) is sandwiched in-between two walls of cob? Very interesting!

And thanks for the book reference!


No. It's a homogeneous matrix like concrete. Check out wood chip clay. Mine is similar. But I'll use large chunks of wood as well.All built within a sturdy post and beam structure with the roof and RMH in place before the walls are filled in.
This message was edited 2 times. Last update was at Today 9:51:31 PM by Dale Hodgins
Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
I Googled wood chip clay and was fascinated to learn about this technique. I'd never heard of it before and I've been researching this stuff for a while now.

From what I can tell, the spacing between studs must be smaller than when using cob or straw bale. The photos I've seen make it look almost like a traditional stick-frame house. I'm wondering how that affects overall cost, since such a house would require a lot more wood.

How exciting that such a structure is being built in my neck of the woods. I hope you'll post here about your project - I'd be really interested in learning more, plus coming up to see it some time. Many thanks, Dale!
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Mine will not have studs. The walls will be at least 14" thick framed with wall trusses spaced 2 feet apart, held in place with strapping and everything covered with earthen plaster. I have to get it through city hall.
Gail Moore


Joined: Jul 09, 2011
Posts: 142
Location: south central Appalachia, southwest Virginia, US zone 6/7
    
    1
First Officially Permitted LOAD BEARING Strawbale Home built in New Mexico

http://www.pajaconstruction.com/projects.htm

Quote:
"We are closing in on completing New Mexico’s first permitted ‘loadbearing’ structure (in loadbearing, we stack up the bales and then put the roof’s weight directly onto those bales) and have been rewarded with some out-of-the ordinary obstacles as well as wonderful compensations. On the positive side, we’ve once again become wildly enthusiastic about just how easy it is to build loadbearing; we’ve also enjoyed the looks of astonishment on our visitor’s faces changing to grins of comprehension as they ‘get’ the full environmental benefits of not needing nearly as much wood. On the challenging side, we wrestle with convincing our friends in the Construction Industries Offices that this really is a legit and long-lasting method; and we continue developing new methods of attaching interior walls to floating trusses or window openings to the straw. Do visit the project gallery and follow the progress with us! We have also created a smaller showcase gallery that you can visit on this site."


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Rusty Bowman


Joined: May 30, 2009
Posts: 124
Location: Idaho
    
    1
Mariah,

Sounds like you are doing a great job on your homework! That said, I'd suggest checking out the book "Design of Straw Bale Buildings: The State of the Art" by Bruce King. While not a cookbook on strawbale recipes, it'll arm you with the kind of info you seek. Written by an engineer, it is quite technical...and has few if any pretty pictures and can be rather tedious. That aside, it's the most info dense up-to-date scientific book on the subject.

Re the quoted R30 for cob by an earlier poster....I do not know how that would be possible. Folks at the Oak Ridge National Laboratory found two-string straw bales, laid flat, to only have an R26 which, is quite a bit lower than once believed. I am not aware of any similar scientific testing of cob but it goes to reason that it would be considerably less than straw bales.

Sounds like you are fortunate to be in an area with good cob experience. Perhaps you could tour some of the cob structures there this winter.

Good luck.

rusty


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pahanna barineau


Joined: Oct 03, 2010
Posts: 47
cob is fair as a insulator and fair as a heat storage material, i poured a 2" thick wall beside my woodstove and with the stove super hot, i could still hold my hand on the other side to the point i put a propane wall mount heater being only 6' from the woodstove with no worry, The Passive Solar Energy Book by architect Edward Mazria [1979} is full of information on the heat storing/insulating qualities of different materials as well as sizing glass for passive solar building
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Rusty Bowman wrote:

Re the quoted R30 for cob by an earlier poster....I do not know how that would be possible. Folks at the Oak Ridge National Laboratory found two-string straw bales, laid flat, to only have an R26 which, is quite a bit lower than once believed. I am not aware of any similar scientific testing of cob but it goes to reason that it would be considerably less than straw bales.

Good luck.

rusty


Fanciful stories are rampant amongts cob enthusiasts. On Saltspring Island it has taken on religious tones. I've been accused of blasphemy.
pahanna barineau


Joined: Oct 03, 2010
Posts: 47
you got admit the price of it is rather holy compared to others
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
The laborious nature of the material has brought many to their knees , praying for a better way.

And that's where my machines will come in handy.
gary gregory


Joined: Apr 09, 2009
Posts: 395
Location: northern california, 50 miles inland from Mendocino, zone 7
My friend Anthony has designed and supervised several straw bale projects. One on the Oregon coast, 100+ inches of rain most years.
architect


Gary
pahanna barineau


Joined: Oct 03, 2010
Posts: 47
i know what you mean about cob bringing you to your knees, i will not build another dome with less than a five person crew, i have built many houses and 3 people can build 10 times faster than 1 person
Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
I'd like to learn more about this wood chip/clay Dale speaks of.

Dale, you said your walls would be 14" thick. How did you arrive at this number? What steps are you taking to ensure proper drying through such a thick wall before being able to apply plaster? You said you will have a rocket mass heater installed ahead of time, is this the ticket? I seem to recall someone saying that letting cob (standard cob) dry by applying heat can cause it to crack, etc. I guess this isn't as much an issue with wood chip/clay?

I'm really intrigued by this technique. I can see it would save a lot of labour compared to cob, and provide one with clean straight walls (since that is my thing; I get it isn't for everybody). Wood waste is so easily come by here. Do you know of anybody who has used this technique in this area? How did you come up with the idea?

Perhaps I should start a new thread on the topic, if there isn't one in the archives somewhere...

Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Mariah Wallener wrote:I'd like to learn more about this wood chip/clay Dale speaks of.

Dale, you said your walls would be 14" thick. How did you arrive at this number? What steps are you taking to ensure proper drying through such a thick wall before being able to apply plaster? You said you will have a rocket mass heater installed ahead of time, is this the ticket? I seem to recall someone saying that letting cob (standard cob) dry by applying heat can cause it to crack, etc. I guess this isn't as much an issue with wood chip/clay?

I'm really intrigued by this technique. I can see it would save a lot of labour compared to cob, and provide one with clean straight walls (since that is my thing; I get it isn't for everybody). Wood waste is so easily come by here. Do you know of anybody who has used this technique in this area? How did you come up with the idea?

Perhaps I should start a new thread on the topic, if there isn't one in the archives somewhere...



I think 14 inches would be a minimum figure. It will depend on what I can get approved. Wood chips dry out the cob by wicking water around and the irregular rough surface gives the wall huge surface area. I plan to leave the walls un-plastered until sufficiently dry and install the stuff with less water than is typical since it will be tamped together as in rammed earth construction. The RMH will speed drying.

I've never heard of this particular technique before. About 25 years ago when I was 22 I read about woodcrete blocks being made in Germany. Around the same time I read about Rob Roy and cordwood building. I knew right away that I don't posess the patients for all of the fiddly detailing involved in that process and all of the work of keeping the log ends clean. I also checked out adobe but it makes no sense in Canadian winter conditions. Within weeks I had concieved of this system and it's ability to use anything wooden in the mix. For 20 years I've called it woodobe. I married someone who has never shown any interest in innovation and a quarter century has passed. It's been stewing in the back of my mind ever since as I pursued other businesses. I'm single now and have the perfect property for it, being 1 mile from a cedar mill and having other resources at hand. I will be a part time inventor from now on.
Rusty Bowman


Joined: May 30, 2009
Posts: 124
Location: Idaho
    
    1
Mariah Wallener wrote:I'd like to learn more about this wood chip/clay Dale speaks of.

I'm really intrigued by this technique. I can see it would save a lot of labour compared to cob, and provide one with clean straight walls (since that is my thing; I get it isn't for everybody). Wood waste is so easily come by here.



Here are some photos of a little structure I built a few yrs back using free wood waste. Some call the technique "chip-slip". I used 3 parts wood chips to 1 part clay slip and mixed in a small amount of Borax as a natural mold inhibitor. This slurry was tamped into standard 2x4 walls with slats providing a key. I used plywood for forms...screwed to the studs. The forms could be moved up immediately.

Before applying the earthen plaster over, I used an adhesion coat on the interior face of the studs consisting of wheat paste, horse manure and sand. I spragged the exterior face of the studs with sheet rock nails....to provide a tooth for the earthen plaster and prevent cracking due to the different drying rates between the wood and plaster. Working great thus far.

Mechanical mixing (ie, concrete mixer) would make this job far easier. I mixed every thing by hand in a wheel barrel. It was tiring but I believe it to be quite fast and easy compared to many other natural building techniques.

I have no idea on the R value....but per inch, it's probably pretty low. Stands to reason that it would be a fair bit better than COB though.

The unfinished walls make for a great surface for earthen plaster...and you can get it quite straight/even with little effort.



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Rusty Bowman


Joined: May 30, 2009
Posts: 124
Location: Idaho
    
    1
Here's a pic of the almost finished project. Earthen plaster inside and out. For a finish, clay paint was enough for me on the inside. On the exterior, there's nothing but the single coat of infill plaster, hence the patchiness.





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Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
Rusty --- Is that recycled concrete by the foundation? What sort of shrinkage from the studs did you encounter? What was your dry time? How long did you wait before plastering? Because of our much wetter climate, I'll need big roof overhangs and I may stucco the bottom 2 feet so that wet snow can't soak the wall.

Mariah --- There's a thread about straw clay. The same machines could be applied to chips. On YouTube there is a video called " The six minute straw clay house". It shows a highly mechanized crew. The links lead to more primitive styles.
Rusty Bowman


Joined: May 30, 2009
Posts: 124
Location: Idaho
    
    1
Dale Hodgins wrote:Rusty --- Is that recycled concrete by the foundation? What sort of shrinkage from the studs did you encounter? What was your dry time? How long did you wait before plastering? Because of our much wetter climate, I'll need big roof overhangs and I may stucco the bottom 2 feet so that wet snow can't soak the wall.


Dale,

Yes on the recycled concrete. I just drystacked it there after the fact to a) get it out of the way and b) to keep splashback off the plaster. I used recycled bricks for that section of foundation and recycled concrete on a section of foundation not in the photo.

I did experience some shrinkage....perhaps 1/8" at the studs or so. The clay I used is quite expansive though (& it was 100% clay). To counter and give the chip-slip something to key in to, I nailed 1x2's, on edge, to the studs. For extra reinforcement, I attached horizontal slats between. The stud width was about 20-24" as I recall. On a test wall, this method proved to be a lot stronger and more stable then simply spragging the studs with 10d nails only. The key seemed to be getting a thorough compaction within the forms. That would be easier in something wider than the 2x4 wall I was working with.

Re dry time and time to plaster.....it seems I waited 3 weeks if not longer...maybe 4 wks. It was late summer and relatively dry. It just waited until I could physically not detect the sense of moisture on the back of my hand and lips. With the earthen plasters permeability, combined with borax, I reasoned that a small amount of moisture deep within would be ok. I ran some heaters inside after plastering for extra precaution.

In addition to your large overhangs, perhaps you could put a temporary wall of sorts (like a row of straw bales on edge) around your bottom 2' to keep snow off the wall....set back away from the wall to allow air movement. That's assuming I'm understanding correctly that you were concerned about keeping moisture off that area while waiting for the chip-slip to dry before applying your finish. (just thinking aloud....)

rusty
Dale Hodgins
pollinator

Joined: Jul 28, 2011
Posts: 4242
Location: Victoria British Columbia-Canada
    
  62
No, the stucco would be permanent. It's meant to do the same as your stacked concrete, to protect the wall from splash back. I'm going to completely envelop my framework under 2 inches of cob to eliminate the cracking issue and to gain thickness. 2 1/2 inch nails driven 1 inch into the posts will ensure that materials stick to the posts. Thanks for the info.
Jason Mendes


Joined: Dec 09, 2011
Posts: 15
Greg Hickey wrote:Mariah,

However it is not load bearing and thus only an infill that needs a rigid frame structure in addition to the straw.


I actually thought that bales /can/ be load bearing, such as in balecob walls. I've seen in person bale walls with rafters loaded on them, and with the ridge beam loaded.
Jason Mendes


Joined: Dec 09, 2011
Posts: 15
Mariah Wallener wrote:I didn't think strawbale was an option since our climate is quite wet (i.e. high humidity in winter).


What area are you in exactly?
Mariah Wallener


Joined: Feb 02, 2011
Posts: 144
Location: Cowichan Valley, Vancouver Island, Canada
Hello Jason. I am on Vancouver Island in the Cowichan Valley.

And yes, straw bale can most definitely be load bearing.

I've since discovered that it is common practice in my area to use straw bale on north walls and to sandwich them between thick layers of cob. Should any moisture (in the form of vapour) get trapped in the bales due to our humid winter conditions, the cob acts as a wick to draw that moisture out of the straw and into the cob where it won't do any damage.

Plans for our house are proceeding and I am going to start a new thread in the "cob" section, even though we're looking to do clay/fibre (wood slip).
 
 
subject: Strawbale in the Pacific Northwest, anyone?
 
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