Cob: strawbale/cob on the inside

[Matthew HALL(SED)]

Kerry
Very interesting concept. It makes good sense to me to have the cob on the inside wall and the
straw on the outside. Radiant heat loss to the atmosphere from the cob thermal mass store will be
minimised by the high insulation layer of the strawbale. How will you ensure the strawbales are
durable enough to withstand your climate? Cement-based render perhaps? Lime may be better as it
would allow the structure beneath to breath; very inportant if you want to prevent rot in your
straw bales.

>Just thinking about building in my area, cold Alberta Canada.  I am a
>huge lover of the cob concept but in my climate I am feeling and have
>been told by experienced  cobbers that it may not be a positive thing
>for up to  -30*C weather.  
Cold is only a problem if there is also moisture. Without it there cannot be frost and so your
material won't get damaged in this way. I remember you told me your climate is very dry but cold so
you may be okay. Make some trial samples and leave them outside to see what happens.

>
>Now, if I  prepare my interior walls with   stucco, cob, whatever ( to
>cover the bales)  how do I attach  cob structure (ie.  furniture, stoves)
>to these prepped walls without the cob structures falling off? Do I have
>to cob around rebar attached to my walls?   Will
>my house move and crack the interior cob?
Cracking can be reduced/prevented with adequate use of natural fibres in the mix. You may also be
able to leave some extra long fibres exposed from the wall to help tie your furniture in with the
wall itself. If you use rebar make sure it is embedded very deep to prevent rust forming. Hardwood
may act as a better framework for your furniture and it too will be preserved if embedded
correctly. 

>>Is my idea feasable? 
Yes, very much so. I have seen buildings like this before with an insulated earth wall as you are
describing; rammed earth on the inside and straw bale or other insulating material on the outside.
It should not add too greatly to the cost but your walls will be immensely thick and you will need
a lot of labour to build this project!
Good luck
Matthew
____________________________________________________________________
Matthew Hall - PhD Research Student
Centre for the Built Environment
Unit 9 Science Park
Sheffield Hallam University
Pond Street
Sheffield S1 1WB
England

Tel: +44 (0) 114 225 3200
Fax: +44 (0) 114 225 3206
E-mail: M.Hall at shu.ac.uk