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cordwood houses

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 15623
Location: missoula, montana (zone 4)
    ∞
Matt of Feral farm shows a tiny house made of cordwood.  This off grid house is also a round house.  Matt talks about the issues of cordwood contrstruction, plus issues with round house construction.

Matt explains that one of the perks of cordwood construction is that once the thermal mass is heated, it will hold the heat for a day. 

The biggest downside for cordwood is that as the wood dries, it shrinks.  So gaps tend to form between the wood and the mortar - thus allowing wind to pass through the structure in hundreds of gaps.  Or the wood cracks and provides a differend kind of gap.  The solution is to  use only thoroughly dried cordwood.  This structure shows the benefit of using using thoroughly dried cordwood.

Matt has done a great job of reusing materials that otherwise would have been thrown away.

Complete with a micro kitchen and a wood stove.  The base under the stove is an old chalkboard! 



http://www.youtube.com/watch?v=j3XRa7SsPQk




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Kate Nudd


Joined: Dec 09, 2010
Posts: 108
Serendipity, as the North American Cordwood conference( CoCoCo 2011) is this weekend at the Alternative Village at the University of Manitoba.
Information regarding it can be found at www.daycreek.com
( a super forum for cordwood builders)
I attended their last conference about 5 or 6 years ago in Wisconsin.
Lots of great shared cordwood building experience to be had there.
                                


Joined: Jan 12, 2011
Posts: 50
I will watch the video's soon, but can youy tell me what type of mortar he used
Matt Ferrall


Joined: Dec 26, 2008
Posts: 555
Location: Western WA,usda zone 6/7,80inches of rain,250feet elevation
    
    4
I havnt had time to change my name on here yet but this is me and Ill happily answer any ?s.The mortar mix is the one from the Rob Roy books.Its been a while since I was mortaring so the exact ratios escape me.


There is nothing permanent in a culture dependent on such temporaries as civilization.

www.feralfarmagroforestry.com
                                


Joined: Jan 12, 2011
Posts: 50
If memory serves me correct, Rob used a lime and white portland? mix? Is that what you used
Abe Connally


Joined: Feb 20, 2010
Posts: 1407
Location: Chihuahua Desert
what not use stones?  there's more thermal mass in stones than wood.  And stones don't shrink.

I've never really seen the appeal of cordwood, though I've never lived in a place where we could just cut trees for building homes...


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Joined: Jan 12, 2011
Posts: 50
velacreations wrote:
what not use stones?  there's more thermal mass in stones than wood.  And stones don't shrink.

I've never really seen the appeal of cordwood, though I've never lived in a place where we could just cut trees for building homes...


except stone has a very poor r-factor. I will be building a cordwood sauna this summer and have some idea's how to reduce shrinkage and cracking
Abe Connally


Joined: Feb 20, 2010
Posts: 1407
Location: Chihuahua Desert
concrete has poor r-factor as well (so does wood, really).  If you surround a piece of wood with concrete, cob, adobe or any earthen mortar, you are totally loosing that r-factor of wood by creating a thermal bridge to the outside.

you are also gaining thermal mass, which wood is very low in.  mixing thermal mass and insulation like that is not a good thing.  They should be layered, not mixed, with thermal mass inside the layer of insulation...
                                


Joined: Jan 12, 2011
Posts: 50
Cordwood construction should never be laid in concrete. Cordwood done properly seams to work well and last a long time. I assume you have read how cordwood construction is done? The ones I've seen that last use a lime mortar which is much less dense than cement or concrete. add some sawdust to the mix and a layer of sawdust in between the mortar layers, with thick walls(18-24" and you get some decent insulation.There should be no cement thermal bridge in a cordwood wall.
I think many also like the aesthetics of cordwood construction.
Abe Connally


Joined: Feb 20, 2010
Posts: 1407
Location: Chihuahua Desert
The mortar mixes I've seen recommended are:
9 parts sand: 3 sawdust: 3 lime: 2 Portland cement

That is not much different than a mortar for masonry. It also makes a decent thermal bridge, it is definitely a lot more dense than wood.

Here a little bit of info that is relevant from wikipedia:
A Western red cedar log has an R value of 1.25 per inch....

However, wood is an anisotropic material with respect to heat flow. That means its thermal resistance depends on the direction of heat flow relative to the wood grain. While wood has a commonly quoted R-value of about 1.25 per inch (depending on the species and moisture content), that only applies if the heat flow is perpendicular to the grain, such as occurs in common wood frame construction. With cordwood/stackwall construction, the direction of heat flow is parallel to the grain. For this configuration, the R-value is only about 40% of that perpendicular to the grain. Thus, the actual R-value of wood, when used in cordwood/stackwall construction is closer to about 0.50 per inch.


So, a 16" cordwood wall would have an r value of of r-8, at best. The mortar joints would have considerably less (probably around R1.6-2).

And one more line from wiipedia:
Although cordwood homes have been tested in -40F locations like Alberta, their thermal efficiency in any climate is below that of a purely cob house of comparable dimensions.


Cordwood done properly seams to work well and last a long time.

In what climate and circumstances? It is definitely not as wide spread or durable as stone or earthen construction.  I have never seen one in my area, and we have many buildings that are 400 years old or more.
                                


Joined: Jan 12, 2011
Posts: 50
Have you read any books on cordwood construction or just Wikipedia? Did you not read this from wikipedia?

"R-value testing was completed at the University of Manitoba in the winter of 2005. The findings compiled by the Engineering Department, found that each inch of cordwood wall (mortar, log end and sawdust/lime insulation yielded an r-value of 1.47"


In this area of Canada and some parts of the upper US, cordwood has a pretty successful history- not the most popular, but successful. I'm not knocking stone masonry, I am a stone mason-for almost 25 years. I know the trade and history well. If you like, we can discuss the pro's and cons of stone masonry. Cordwood masonry also have pros and cons, but done properly and in colder climates, I would say cordwood is superior.

Btw, there a huge difference between Rob Roy's mortar and standard type N, S and M mortar mixes

Matt Ferrall


Joined: Dec 26, 2008
Posts: 555
Location: Western WA,usda zone 6/7,80inches of rain,250feet elevation
    
    4
Thanx for providing the mix info as my books are buried.I have lived in a concrete building and it was impossible to heat.The logs are structuraly important in that they connect the inside layer of mortar to the outside layer and allow for the sawdust insulation in the middle which is the key to making the walls good heat holders.I believe quick growing second growth cedar would be best as it has more trapped air.Im almost done with a sauna made out of old growth cedar because I like the smell and the resins are rot resistant but because the grain is so tight there is less air trapped in the log which makes it less insulative.It should also be noted that I get 80" of rain a year and most days are overcast so thermal mass really does me little good...unless its on the inside of an insulated barrier which the sawdust provides.I love stone too but wood has a softer warmer feel to me.One of my favorite things about CW is how much visual information it contains per sq ft..Rock also has that appeal.Since I lack the funds to build big,I employ the use of detail to create appeal.
                                


Joined: Jan 12, 2011
Posts: 50
Mt.goat wrote:
Thanx for providing the mix info as my books are buried.I have lived in a concrete building and it was impossible to heat.The logs are structuraly important in that they connect the inside layer of mortar to the outside layer and allow for the sawdust insulation in the middle which is the key to making the walls good heat holders.I believe quick growing second growth cedar would be best as it has more trapped air.Im almost done with a sauna made out of old growth cedar because I like the smell and the resins are rot resistant but because the grain is so tight there is less air trapped in the log which makes it less insulative.


Hi, what's the sqft of your little house. Also, in the video you mention lime with the sawdust, did you try a lime mortar mix instead of the 9-3-3-2 mix. In my first experiment, I've had good success with a straight lime mortar mix-3-1/no sawdust. Very little shrinkage-biggest gap is 1/16". I plan to add sawdust to the next mix. Have you any experience with a mix like 3 sand, 1 sawdust and 1 lime puddy?

thanks
glen
Matt Ferrall


Joined: Dec 26, 2008
Posts: 555
Location: Western WA,usda zone 6/7,80inches of rain,250feet elevation
    
    4
Approx. 200sq ft.16` diameter.Yer on your own when it comes to experementing.I followed the books and I finished all my walls at least a year ago and was so bored with it ,I threw away my notes.Im on to cob now.Cob wood black locust coming up.The roof is metal and 20` x 20` and represents the biggest cost.Natural building has alot of hidden costs too like wear and tear on vehicles and bodies.
Troy Rhodes


Joined: Feb 17, 2011
Posts: 262
    
    4
Just for a direct comparison of r-values:

most stone is r-1 per foot

and most wood is r-1 or a little better, per inch.


And the cordwood walls generally have mortar around the inner layer, and around the outer layer, but none in the middle, exactly to provide a thermal break.

So, while there are lots of techniques that can provide better r-value per inch than cordwood, cordwood would still be 6-10 times better than a simple stone wall in a cold climate.  Every technique and material has some strengths and weaknesses.

Finest regards,

please carry on,

troy
ronie dee


Joined: Mar 04, 2009
Posts: 588
Location: Cosby MO
    
    2
Mt.goat wrote:Cob wood black locust coming up.The roof is metal and 20` x 20` and represents the biggest cost.Natural building has a lot of hidden costs too like wear and tear on vehicles and bodies.


Very interesting... I have been thinking about cob for Black Locust stack wood construction for a while now. I'm curious what you will use for a footing and will you put a thermal break in the center of the cob?

What made you go with 20'X20'  instead of rectangular?


Sometimes the answer is not to cross an old bridge, nor to burn it, but to build a better bridge.
daniel mielke


Joined: Aug 13, 2012
Posts: 7
Location: South Central Minnesota, Finally Zone 4
Looks like an older thread here, but to those interested in cordwood construction there is a web site called Daycreek.com. Go to All Things Cordwood. It shows cordwood houses from all over, some of the builders and their stories and where you can get literature from the various builders/teachers and from the Continental Cordwood Conferences from 2011 in Manitoba Canada and from 2005 in Merrill, Wisconsin USA. I have been to two work shops that Richard and Becky Flatau have given and will be doing two cordwood vestibules on either side of a pole barn built into a side of a small hill. I am in the process of building a stand alone stone wall around the pole barn and when roofed over and properly insulated it will be an interior cellar for my small vineyard. There is method of cordwood construction is called Double Wall Stackwall Construction and is done by Cliff Shockley. His book is also on Daycreek's site.

As a way of keeping grapes cool while collecting an amount to transport to other wineries, I plan on building a refrigerator within my pole barn. Two of the walls will be insulated exterior walls to the pole barn while the other two will be the Double Wall Stackwall design. In essence this design has two cordwood walls with a interior of stiff insulated material. Mr Shockley constructed a home and other structures and a insurance office for himself in Manitoba, Canada out of reuseable electric pole that the utility there had as waste. He just sawed them into the length he needed, which if I can remember right was about 5 inches long and of various diameters. So to visualize this, you would have two walls of cordwood with a cement mortar "S" mix type I believe joined in the middle by a stiff insulated product to provided for retaining the coldness of the refrigerator. This will be a post and beam construction with the stackwall as in fill. The type of wood you would use is the most important part of this type of construction. YOU CAN'T USE HARDWOODS!!! When they get wet they will expand and completely break your wall apart. Soft woods are what you need, they don't expand like hardwoods. On my site I have many cottonwoods that I have cut down and some of which are completely dry indoors and will be in the refrigerator part. Others are still whole logs from seven to eight years ago loggings I did locally. And as some of those are a bit rotten I still have enough to build my vestibules and have a bunch left over Hugelkulture, Yeah!!!

Will start my own post forum as to the construction of this site with pictures in the near future. One last thing about Cordwood Construction...It is very labor intensive. It looks great but can take a long time, so getting lots of help for doing this is an absolute must.
steve pailet


Joined: Dec 01, 2012
Posts: 35
I think cordwood is one on of the most esthetically pleasing ways to finish a building.. Guess a few quick notes. Never start a building where you are under two feet above the ground. . partly to keep bugs from moving in and eating your handy work.. second when water runs off a roof it tends to splash.. getting your foundation up this high is a good idea so that you wont get staining and rot from the water.

the foundation should be two foot high above grade.. and wide enough to accommodate a double row of mortar about 6 inches wide on the inside and the outside.. as one of the comments here talked about not having a thermal bridge... this will leave an air gap of about a foot when using 2 foot logs.. 2 foot logs is another good idea.. for a variety of reasons.. stable from a stacking perspective.. high r value You may wish to drop in styrofoam beads in the air gap to increase insulation value and as some have noted.. fill the gaps so you dont get wind infiltration as the wood will shrink some.

Another important thing to remember wood dries at about one inch per year. So with that in mind along with less problems with checking and splitting.. keep your wood at less than 6 inch diameter ... Your back will appreciate it ... and the end result will also be more attractive

Cut your wood in the early fall stack it so the wind can work its magic and dry it.. When you cut the wood leave it in 8 foot lengths.. easier to move.. and in the spring.. you should be able to peel the bark right off using a roofing tool that looks like a flattened out hoe. then you can cut the wood to 2 foot lengths.. dont do what some have done and discovered after all the work.. trying to use 6 inch long pieces only to discover just how unstable it is to stack.

In some ways doing cord wood is similar to earth bag.. you have to build bucks for windows and doors and attaching the roof will give you similar problems.. but atleast you can peg on a top sill plate though it is not easy to keep the roof from lifting in really high winds.. so think about what you are doing..

Type of wood.. generally better to use either very dense wood that has a low shrinkage or use softwoods like pine larch cedar or fir. These woods tend not to split which makes sealing wall tough..


As to mortar.. lots pf ideas from paper crete to using the saw dust from your cuttings to fill the mix. I think it is not the real problem.. it is wood shrink and thermal bridging that make it more interesting..

Lots of folks go with round buildings.. inherently strong structure.. or use lomax corners if they are doing rectangular shapes..

As to my preferences .. I would really just use cordwood if you have a great deal of trees available (softwoods) and use them in a variety of out buildings from storage to sauna...

I recognize that people want to live as close to nature as one can.. but doing all of this work and failing to protect the investment in time and labor.. keep the wood off the ground and consider really really wide over hangs on your roof.

That said.. I am building with Sips.. great use of crap wood to make OSB.. super insulation.. makes building super fast.. tight.. and over time.. the amount of real maintenance and resale all factors
Rachel Baklinski


Joined: Aug 12, 2013
Posts: 1
Hello, is anyone currently building a cordwood house in central/eastern Ontario, or recently built one? I'd love to chat about your experience thus far and how you went about design approvals/house inspector approvals, etc. Thanks!
Kate Nudd


Joined: Dec 09, 2010
Posts: 108
Rachel,Hi
Over at the www.daycreek.com site is a forum specific to cordwood building...you might find someone in your area.
I helped with a cordwood build a few years ago in Manitoba and found the connection from that site.
All the best.
Kate
 
I agree. Here's the link: http://richsoil.com/email
 
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