[Strawbale] Green roofs on strawbale buildings
ArchiLogic at yahoo...
Fri Sep 17 23:48:14 CEST 2010
On Fri, 17 Sep 2010 14:37:51 -0400, Derek Roff <derek at unm...> wrote:
> I know of two post and beam strawbale houses, where one or more of the
> posts does not touch it's pier at the bottom.
> OK, RT, tell me where I've gone wrong.
Sheesh, I come in to relax a spell with a nice cuppa tea and I find this
message from that pesky Derelict *demanding* an answer.
I'm going to guess that the P&B SB home in the Derelict's example is
(1) relatively small (or if not, has relatively short-span joist or rafter
(2) subject to relatively small live and dead loads
I think that even the most sceptical amongst us knows that reasonably
dense straw bales (ie compressed to 120 kg/m^3 or more) provide
sufficient compression resistance to demonstrate minimal to negligible
deflection under the stresses imparted by the dead loads that are
associated with modest-sized residential structures and in situations
where the live loads are relatively small (say 2.4 kPa as a number pulled
out of my hat, unsubstantiated by nothing more than my gut) in conjunction
with those relatively short spans ... may very well exhibit minimal
deflection as well -- initially.
But beyond certain stress levels (as can easily happen with the larger
spans, larger building sizes and/or higher gravity loads) the bearing
capacity of the straw will be exceeded no matter how well they were
Any chart from compression tests of unplastered bales that show deflection
values under incremental loads will show where that "tipping" point falls.
True, simply using wider bales thereby reducing stress values may work in
some situations but in most scenarios space consumed by structure is not
unlimited so excessively wide walls or grossly over-sized round bale
"columns" are not a feasible option.
Now, I'm hoping that someone else here will comment upon Brian Waite's
instinctual reservations against structural bale sandwiches (although I do
agree with his preference for utilising door and window jambs as slender
I don't have a problem with load-bearing SB walls. The problems arise when
people can't get the roof onto those loadbearing bale walls quickly enough
to avoid rain-wetting of the bales. Short of a temporary over-roof over
the building site, few "rain management" schemes are actually as effective
(Tea time is over.)
=== * ===
Kanata, Ontario, Canada
< A r c h i L o g i c at Y a h o o dot c a >
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