looking for a good book about cob and earthbag building

or one or the other. Anyone have any recommendations?

Curious what climate youre in. What do you expect to get for R value?

"R value"? I am in the Pacific Northwest. I'm not hoping to build here though, just want to learn more about it.

R value is how insulating a material is.  Earth does not generally have a great R value - it is more thermal mass than insulation.  Great for desert climates with hot days and cold nights, because of the thermal flywheel effect.  Acceptable for climates with mild winters, but not the most insulating.  Not real good for very cold climates.

The contents of earthbags can modify their R-value, for example some light volcanic tuff can make it a better insulator.  I am not aware of ways to increase the r-value of cob. 

Oh, interesting. Thanks!

Another way to define R value is - a measure of thermal resistance.   Earth has a value of thermal resistance, but other materials are better at resisting thermal movement. (Things like insulation - polystyrene etc..)

Here's the wiki link:      http://en.wikipedia.org/wiki/R-value_%28insulation%29

Earth/dirt  has an R value but cob + straw or wood or some other insulation material would have better R value than just dirt alone.
Dry dirt has better thermal resistance than wet dirt... wet dirt would transfer the heat faster.

Imagine you have a roof over your head and no walls to give resistance to heat loss... You build a fire in your wood stove under your roof and the heat just goes out in all directions  without any resistance. You are cold.  So now you wrap a thin sheet of plastic all the way around as walls and you have an R value of  around  1.  wuhuu you are not so cold... The more insulation material you add to your roof and walls - the easier it is to keep your heat in and the more R value you have  (Keeping your insulation dry is important  too.)

One inch of cob has a small  R value and one foot of dry cob has a greater R value.

Ohh, I see! Cool. So does a cob house have a high R value?

The thicker it is the higher the r value. Adding straw should make the r value higher too.

The cob Ive seen does not have a high R value. In fact, most would not even meet the local code requirements. However, as most people on this site use wood to heat with, it might still be the best choice for your situation.

I agree with ronnie except for thin plastic sheeting having an R value of 1 or that an R value of 1 would make a difference.
Plastic sheeting doesnt really have any R value but it has long been used as an air barrier in very cold climates.

Stopping Air infiltration is MUCH more important than R value. I see some cob installs having this as an issue as well due to splits in the wood over time. Surely a cob expert can tell me Iam wrong on this or there is a technique to avoid it..

I think that it would be best for people to stick with DOE bare minimum R value levels. Found a cool link thats adustable based on heating/cooling source and ZIP code: http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html

check out "The Hand Sculpted House" By Ianto Evans, Micheal Smith and Linda Smiley   A great book for cob. Was written in Oregon as well.... go Pacific Northwest!

Also important for understanding of Cob, it does not function because of its R-value ( very low) It functions on a thermal mass idea. It traps heat when the sun shines and gives it back when the sun goes down. Very good for moderating temperature and humidity, as cob will absorb moisture form the air. The walls breath! If your climate is very cold for the winter with little no solar gains available then a hybrid structure might serve. IE: a north and a bit of your east and west walls made of something with more insulation, then cob in the south.  Good luck.

Mowgli wrote:
Also important for understanding of Cob, it does not function because of its R-value ( very low) It functions on a thermal mass idea. It traps heat when the sun shines and gives it back when the sun goes down. Very good for moderating temperature and humidity, as cob will absorb moisture form the air. The walls breath! If your climate is very cold for the winter with little no solar gains available then a hybrid structure might serve. IE: a north and a bit of your east and west walls made of something with more insulation, then cob in the south.  Good luck.

Awesome, thanks! And I actually just ordered that book! Yay! Can't WAIT to read it.

ECO Sense says regular cob has r-value of about .5 per inch - so r=1 per two inches.

http://www.islandnet.com/~anngord/builders.html#slic

Check their section on "SLIC."  They also get higher r-value by additives.

Oregon also has desert regions as well as it's rainforests and coasts. I believe Jackson Oregon is in the desert region, where many of the cob builders are experimenting.

Here is a blog by a man who built a cob back east in snow and humid regions. The lessons he learned are invaluable. http://www.small-scale.net/yearofmud/
The Year of Mud blog