[Cob] Cobwood in Montana - Reply

[Frank Hanlan]

Hi Sky,
I live in Edmonton, AB so I assume that our climate is similar to Montana.  Key factors that occur to me are rain/water protection, thermal bridging, insulation requirements both walls & floor (I am an old timer so I still use R values) , air tightness and thermal mass.  Also think of this as what you need/want for the next 30 to 50 years.
If you are using slab on grade or similar construction consider R10 to R20 under the slab/floor (heat loss through slab and basement more significant than what we believe in 1970s & 1980s.  Thermal mass is great for holding heat or cool and moderating temperature swings but needs thermal separation from materials connecting to outside.  Net zero and near net zero houses in Edmonton are using thermal mass ie concrete floors on main and/or 2nd levels, inside south facing windows to hold heat in heating seasons and have overhangs to shade them in cooling seasons.  In cooling season thermal mass also holds cool air from night time and/or early morning.  
Air tightness is critical to keeping warm air in heating seasons and cool air in cooling seasons but also keeps in moisture and outgases from materials. Avoiding thermal bridging also helps so possible consider post and beam (could use trees/lumber that has been dried) with double wall system using Larsen trusses or modified Larsen trusses as down by Riversong.  A 10" space full of cellulose is only about R30 and less with thermal bridging.  I would recommend at least R40 for walls in Edmonton and R60 in the attic.
Also ensuring rain/water protection and air space for exterior wall system so that it can both shed water, drain easily and dry out during dryer times.
Sincerely yours,
Frank Hanlan

Edmonton, AB

If you have not demonstrated that you can hear the true state of the world and still act then don't expect to be told the truth.  

Despite of the agreement in Cancun, Mexico we have still a great amount of work to do to ensure that global greenhouse 
emissions have peaked and started down by the end of 2015 and to keep the average temperature rise under 2C to stop
widespread flooding and the displacement of 400 to 500 million people.

> From: coblist-request at deatech.com
> Subject: Coblist Digest, Vol 9, Issue 101
> To: coblist at deatech.com
> Date: Sat, 23 Jul 2011 12:00:02 -0700
> 
>    1. Feedback on cobwood? (Sky Orndoff)

> Hi everyone!
> 
> We (my friends Kyle, McKenzie, and myself of EarthArtBuild) here in Montana are 
> in the process of building a cobwood (like Rob Roy's Cordwood) addition to a 
> conventionally framed building.  We have already built two other cordwood 
> buildings on site, and due to Montana's extremely cold winters don't really 
> appreciate the thermal mass.  Once it cools down, it's hard to heat up.  And we 
> aren't around all the time to keep the rocket mass heater burning.  So we've 
> tried to minimize the amount of thermal mass in this building.  
> 
> 
> The design is this:  4 inches of cob, 10 inches cellulose insulation, 6 inches 
> of cob.  This sandwich is penetrated frequently by a 21 inch log round.  The 
> walls are going up, and that's the way they're going to go up, unless someone 
> says "STOP, RECONSIDER" in a way that's truly convincing.  But feedback and 
> predictions on functionality would be very interesting; please comment!  The 
> room is small (8 feet diameter, about 3/4 of a circle) so the rocket mass heater 
> which we've already made should work quite nicely.  If you want to see pictures 
> and video of the project, check out www.earthartbuild.wordpress.com.  And please 
> comment or reply via the forum or the website.  Thanks!
> 
> Sky Orndoff, 
> 
> EarthArtBuild
> 
> 
> ------------------------------
> 
> _______________________________________________
> Coblist mailing list
> Coblist at deatech.com
> http://www.deatech.com/mailman/listinfo/coblist
> 
> 
> End of Coblist Digest, Vol 9, Issue 101
> ***************************************