[GSBN] Question on straw-bale house foundations

[RT]

On Thu, 15 Sep 2011 14:56:19 -0400,

Alex Wilson wrote (via Duck Foo'd) to the GSBN List:
[snipped & mangled]

>> My cousin ... considering building a timber-frame/straw-bale
>> house  ...foothills of the Rockies of southwestern Alberta.

>> thinking that he might save money by avoiding a full perimeter
>> foundation--and going with piers or something like that.

>> The Chinook winds there are wicked, so I think a rugged timber frame
>> is an absolute must with straw-bale. Right near the ranch, they've
>> recorded a _full week_ where the steady wind _never dropped below 60
>> mph_ and a full hour where the steady wind never dropped below 100 mph!

(For full text of original message and ensuing thread see GSBN archives

     http://sustainablesources.com/pipermail/gsbn/2011q3/000067.html
)

Alberta Rockies ... lots of rock readily available maybe ?

(If there's any roadwork or construction going on nearby there's likely  
blast rock that the contractor needs to dispose of so they'd be happy to  
deliver the rubble to the site free of charge, and if well-planned, dumped  
in such a fashion so as to require minimal work to level it.)

If so, I think that I'd look at building a stone plinth (massive boulders  
at bottom followed by smaller stuff (say 6") followed by 2" and then  
topped off with 5/8" or smaller, all well compacted ...) on which a  
perimeter grade beam would be cast and to which the SB structure would be  
well-anchored... and then fill in the interior area of the grade beam with  
more rubble followed by superinsulation and then a floor (earthen or stone  
or concrete or [insert your choice] on top. The stone plinth could be  
fashioned to provide multi-levels if desired and have channels inserted  
for accessible service chases).

I suspect that the amount of concrete consumed for the grade beam would be  
comparable to that required for the piers + pier footings, if not less  
(depending upon the bearing capacity of the sub-strata at the site).

However since the floor is cast on top of compacted stone rubble  
(essentially a very good roadbed), the not-insignificant cost of the wood  
framing for joists, beams and decking would be eliminated along with the  
long-term headaches associated with suspended floors over crawlspaces.

I'd also look at sculpting the earth around the site to create berms that  
will reduce or eliminate the wind intensity affecting the building site.  
Even better if large caliper (ie 15 cm or larger) conifers can be  
rescued/transplanted into those berms to create windbreaks.

Which of course raises the question: Would some other building type be  
better-suited to that site ? (ie partially earth-sheltered ) rather than  
something that sticks up out of the landscape just begging to be  
racked/rocked/rattled/ripped by a good wind ?

(And I suspect that there are more than a few who would debate the  
assumption that a "Good rugged timberframe" would be necessary to provide  
the necessary racking and shear resistance for SB walls.)

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
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