[Cob] Cob basement is not advised - failure likely due to "rising damp" or "penetrating damp"!

[ocean]

(Before reading my post, please read a great discussion of these issues 
in the references to "rising damp" and "penetrating damp" on this 
website - http://www.periodproperty.co.uk/article004.htm )

To begin, I can hear Ianto Evans chuckling (or scolding us) for some of 
the suggestions and speculation recently about underground or "bermed" 
cob.  I am sure he would have a lot to say on the subject, but he 
doesn't seem participate in this forum - to busy getting his hands 
dirty in the mud.  If he were reading the posts about the cob basement, 
here are some concerns I think he might raise...

Cob by its very nature need to be above ground, built upon a fairly 
high "plinth" or stone foundation.  This provides the moisture break 
from the ground, one of the enemies of cob.  The strength of cob is 
only possible if it has the chance to be come "bone" dry, and to do so 
cob needs exposure to free air on BOTH sides.  Many medieval cob 
structures are failing in Wales after the application of cement stucco 
or latex paint on one or both sides of the cob.  The impermeable 
surface traps moisture within the cob (which may have held up for 
centuries), and then the straw rots and the cob fails.
So underground cob with a moisture barrier will necessarily prohibit 
the cob from ever drying, and ultimately result if failure of the cob 
to support the load - walls collapsing, roof falling in, crushing 
inhabitants.

To the original post person - please rethink whether you really need to 
violate the building code and go higher than 10 feet.  What about a 
sleeping loft which is just 4 feet tall.  Or rething that you really 
need to ask permission from local officials to build with cob...

Good luck!

Ocean

>> Fellow Cobians and wannabes,
>>
>>   We have recently been informed by a (Linn) County, Oregon building 
>> inspector that we can build all the cob cottages we want without a 
>> building permit providing they are separated by at least 3 feet; that 
>> the highest point of the roof is not more than 10 feet above ground 
>> and that they are not larger than 200 square feet. (We want to get 
>> this in writing on County stationary/correspondence before we begin 
>> construction)
>
> What you are describing is roughly the current definition for 
> unpermitted structures (such as accessory buildings) given in the 
> international building code (which Oregon has adopted at least in 
> part).  Unfortunately, my recollection is that the 10 feet given in 
> the code is not "above ground", but rather from it's lowest to highest 
> point.  There is no provision allowing these to be used as a 
> residential structure, and any plumbing and/or wiring must still be 
> permitted and inspected.  I'm not saying you can't live in it, that's 
> your call, however, be aware that legally it won't be a house.  I 
> would recommend getting a copy of the current Oregon codes and reading 
> them rather than relying on anything verbal from the county (you're 
> probably safe on anything they give you in writing, but even that is 
> no guarantee), many libraries carry or can get copies of local 
> building codes.
>
>> A 200 square ft cob structure would fit our needs if it had 2 stories 
>> (400 sq. ft.). A way to get around the 10 foot roof height limit for 
>> a 2 story structure would be to have the bottom floor be below ground 
>> level at least 2 feet (3 feet would be better).
>>  No cob construction literature I have read covers the subject matter 
>> of below ground living space. No Cob workshop I have seen offered has 
>> this topic on the agenda.
>>    Why?
>
> Because buried walls must be able to handle the lateral loads of all 
> the earth surrounding the building, as well as all the moisture 
> wicking through the ground, and any possible running/standing water 
> that may get channeled by the surrounding earth into direct contact 
> with the walls. Simply put, cob is not up to this.  I don't mean this 
> can't be done, however, to do it safely would not be easy.
>
> Shannon C. Dealy 
>