Cob: RE: timbers in cob ??

[Rick Fisk]

Hehe I didn't reply to all when I originally sent this....


In the Cob workshop I attended in Southwest Texas, this wasn't an issue.
I wouldn't call myself authorative by any stretch of the imagination but
I don't see why anyone would suggest that Cob cannot be load bearing or
that you would want to avoid using cob for that purpose.

At Patricia's place (http://www.twistedroad.com) we cobbed directly onto
the ridge beam and used the outside walls as the support for the ridge
beam. If the walls are thick enough why shouldn't they be able to easily
support the roof?

At the above site you will see that the round bale house that Patricia
built has a cob column directly in the center which sole purpose is to
provide the majority of the load bearing stricture for the roof.

If the columns are thick enough they can hold quite a bit of weight as
long as they are shielded from the elements. I suppose the trick is not
to over engineer the roof such that it presents a problem. Ie; don't use
a 2000 year old redwood log for the ridgebeam on walls that are only 18
inches thick in a 200 square foot cottage.

(http://www.twistedroad.com/Cob_Studio/CobPh6/cobph6.htm)

This ridge beam was considered to be much more than cabable for the task
but sits directly on the cob walls as you can see in the photo above.
The beam weighed about 150 lb's and we set a groove in the wall using
machete's and a strange ax that somebody brought in order to level the
beam. ( The blade was at right angles to the handle and was a nice width
for trimming and also had a claw at the opposite end of the "ax"). The
current consensus with Ron and Patricia was that they would hang the
rafters in an arch starting at one end of the ridge beam (rafters hung
at the bottom) gradually increasing up the face of the beam (rafters
hanging from the top of the beam) back to hanging rafters at the bottom
of the beam in order to produce a curved roof using a straight ridge
beam.


Another thing we did to secure the roof in the case of high winds was to
create stakes which were driven into the north wall and would be used as
a means to wire the roof to the wall. 

It certainly would be nice to know if there are specific load tests on
cob but I suppose that the varying qualities of cob mixes would make any
generic measurement moot. 

If they can build 10 story tall apartments in Yemen which have stood for
quite some time, I would suggest that the load bearing qualities of cob
are quite good.


Rick...

> -----Original Message-----
> From: owner-coblist at deatech.com [mailto:owner-coblist at deatech.com] On
> Behalf Of cj & ns .
> Sent: Thursday, April 25, 2002 5:10 PM
> To: coblist at deatech.com
> Subject: Cob: timbers in cob ??
> 
> Hi,
> 
> i've been going thru the coblist archives (96 & 97 so far) and have
seen a
> lot of postings about cob walls & and various issues regarding those.
> 
> did not see any postings about fixing a timber roof framing to the
walls.
> kinda important, ha?
> 
> i am sure those who built their cobbies have experience to share in
this
> rather tricky area.
> 
> cheers
> 
> chris j
> oz
> 
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