Cob: Good Foundations

[lightearth at onebox.com]

Michael

We've done drained gravel less then the frost line here in Wisconsin and Illinois...in that case drainage is the key as heave is based upon upward pressure from water expanding in volume when it freezes. Many foundations in cold climates do NOT go down below the frostline and are fine but require different considerations. Not having moist soil around and UNDER your foundation appears to be A key factor.

One that I like is to keep the foundation both warmer and dry. Many times I've seen foam insulation placed on the outside of the trench to prevent the outside freezing ground from wicking all the heat stored in the foundation away (Option 1). A better version of this would be a 'skirt' that extends down and out away from the foundation, thereby insulating out a ways away from the foundation (see sketch below - Option 2). Not that the soil won't get cold but MAY not freeze solid. Surface insulation (straw etc.) can even keep soil below it from freezing if the soil AROUND the area is also insulated.

3. A third better solution I've heard of and want to try is to keep the soil both warmer and very dry by digging out around the foundation and insulating and sealing from water with Bentonite clay layer. A chemist from Minnesota is planning this for his shallow foundation as the dry soil serves as a good insulation break (commpared to wet soil)and the Bentonite is very natural and long lasting.

Note: this all assumes that you don't have an extremely high water table which adds many other complications for a  needed stiff foundation. Also to be highly considered is the type of soil that you're building upon - clay holds water and expands, sand does not.


Sketches shown without a drain at the bottom of the foundations(highly recommended)

f = foundation
i = insulation (yuck foam or something else)
s = soil exposed to surface freezing temps
d = dry warmer soil
b = bentonite


Option 1

ffffiisssssssssssssssss
ffffiissssss
ffffiissssss
ffffiissssss
ffffiissssss
dddsssssssss
ddssssssssss

Option 2 & 3 (3 is more secure as it drys up the soil behind the bentonite)

ffffiissssss
ffffdiisssss
ffffddiissss
ffffdddiisss
ffffddddiiss
dddddddsssss
ddddddssssss
dddddsssssss
ddddssssssss


with Bentonite

ffffiibssssss
ffffdiibsssss
ffffddiibssss
ffffdddiibsss
ffffddddiibss
dddddddddsssss
ddddddddssssss
dddddddsssssss
ddddddssssssss





-- 
     Marlin Nissen
   - Outta The Box-
  lightearth at onebox.com
(608) 213-9405  Cell/voicemail

"Nothing great was ever achieved without enthusiasm"  - Emerson



-----Original Message-----
From:     puppetman at ix.netcom.com
Sent:     Thu, 8 May 2003 09:07:05 -0400 (EDT)
To:       Coblist at deatech.com
Subject:  Re: Cob: Good Foundations


Thanx D----- for the website reference. That site has me leaning more toward the rammed earth tires for a foundation. I could easily just buy cinder block and be done with it. But I boasted to my wife that I could build my study for under $1,000.00. Her reply; "You go Batman!" sooooo with my Cinva ram costing me $850, and books for R&D at about $100, I need to make my foundation cheap!

I am thinking tires in the core and a cement infill (ala Helen and Scott Nearing's stone walls. The cement will make a surface that I can then slather with a bitumen waterproofing. 

Talked with the township supervisor yesterday and he says the 28" minimum foundation for small buildings is state code and open to interpretation by each township. In my township they are calling it a rat wall rather than a foundation to reduce the confusion, and to keep people from thinking it will hold up their buildings properly. Basically any building under 400 sq ft. does not require a foundation, however they are not responsible when it falls over and kills a cow or two. Supervisor says if you want a building to stand up through more than one winter here, put a four foot foundation under it. 

Supervisor also says berming works just fine and is used alot here to keep from having to dig a four foot trench. Dig two feet and then backfill and berm two feet. Works for me as the test tire I rammed last weekend is Heavvvvvvvvvy. I was not looking forward to being in the bottom of a grave like hole with 250 pounds being lowered down to me. 

The wife still thinks I am crazy but has shown some mild interest in the model I am making in plastilene. 

Thanx for letting me use youall for a sounding board. Please speak up if you think I'm making a mistake or just plain doing this the hard way. 

Michael Fitzgerald
Anthropologist/Woodcarver/Puppetmaker