[Strawbale] strawbale vaults and domes, again

RT ArchiLogic at yahoo...
Fri Oct 15 20:41:43 CEST 2010

On Tue, 12 Oct 2010 15:45:38 -0400, Derek Roff <derek at unm...> wrote:

> You can see some recent dome and vault ideas from Gernot Minke of  
> Germany (building in Slovakia).
> <http://minke-strawbaledome.blogspot.com/2010/08/gernot-minkes-strawbale-dome.html>

Dearest Derlict;

Thanks for the link to the Slovakian SB dome project.
I had seen some chatter about the project on the Euro SB List but hadn't  
yet seen anything of the actual building.

I noted in one of the comments in the blog (quoted below):

================quoted blog material ==============
piatok, 8. októbra 2010

... the moisture levels in the straw bales has been difficult to  
understand. Even after weeks of drying the plaster the moisture level in  
the middle of the straw bales increased from 85%RH to 90%RH. The sensors  
in the straw bales just below the outside clay plaster has been increasing  
with higher outside temperatures and lower with at low temperatures - the  
opposite of what I would expect. The average moisture level in these areas  
are about 95%RH... of course the weather has not been very kind, here one  
of the rainy and windy days, but the clay still seems to be fairly dry.

============ end of quoted blog material ==========

I hadn't had a thorough enough look at the blog to determine when the  
above comment/observation was made -- before or after the EPDM membrane  
was placed over the exterior of the plastered bales -- but the  
(scarily-high!) moisture levels which were increasing
with higher outside temperatures would seem to be exactly what one would  
expect as the sun heating up the exterior plaster would result in moisture  
 from the plaster (covered or uncovered by rubber sheet) being driven into  
the straw via the process known as inward vapour drive, same process that  
would affect wetted plaster on a "normal" Sb wall.

As with any bale construction on which a vapour-impermeable membrane  
prevents transpiration of moisture (whether it be from bulk moisture  
transfer (ie leaks) or ambient humidity, the arrangement *appears*  
problematic. (I haven't delved deeply enough into the blog to see how the  
designers addressed this issue.)

=== * ===
Rob Tom
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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