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GSBN:Climate and SB

Hello all,

...I know that I seldom show up on any listserves these days but wanted 
to toss in my two cents worth on this discussion of the Minnesota failure 
and dealing with moisture in general. Some time ago someone asked during 
a talk I gave whether it wasn't true that you can only build straw bale 
houses in dry places. I agreed. I then added that you can design and 
build dry places in almost any climate.

The critical thing is that we need to be designing and detailing and 
building these buildings according to climate - not just the overall 
climate of a place but the micro climates around the specific site on and 
on different sides of the building. The more the materials you build with 
are subject to moisture damage the more care is necessary. But as I think 
JoE said, the key is building so that moisture that gets in can get out.

Here's the quick and dirty idea of it. If you have seen failed double 
pane windows - two pieces of GLASS separated by the highest tech 
materials we can come up with and built in a factory - what would ever 
lead someone to believe that we could build something in the field, with 
all the varied materials that we use and the extreme variability of 
design and construction skill - and moisture won't get into the building 
and the assemblies? It will, guaranteed. So we should be thinking more 
like the Europeans (new and old - and BTW Canada in spite of its 
proximity is more European than we might think at least where this matter 
is concerned) who assume that moisture is going to get in and think a 
whole lot about ensuring that it can get out. In the U.S. we think a 
whole lot about preventing wetting and pay significantly less attention 
to drying.

You have to figure out for the specific climate and building:
*What the moisture loads are likely to be - i.e. wind driven rain on 
majorly exposed walls or internal loads such as in bathrooms and kitchens 
or firewood storage areas.
*How to deal with each of those loads in a way that reduces the 
likelihood that a lot of moisture will get in - i.e. bigger overhangs, 
porches to protect those areas, rainscreen wall design, and proper 
ventilation of interior moisture in high source areas and elimination of 
the problem if possible - i.e. store your firewood under cover outside, 
vent your bathroom and kitchen (and your clothes dryer!) to the outside 
with an exhaust fan, etc.
*Pay attention to which way the moisture is going to move in your 
location at different times of year and under different conditions. Pay 
attention to some building science - moisture moves from warm to cool, 
high humidity to low, and a lot of moisture can be carried in the air so 
be very careful about having major air leaks into walls from the warmer, 
more humid side of the wall - which can change seasonally in mixed 
*Don't let your bales get wet during (or before construction), don't do 
Santa Fe style (my own long standing bias that is not limited to straw 
bale - the roof should more than cover the tops of the walls or else you 
have a lot of other stuff you need to pay very careful attention to), 
design and build your windows so that ALL the moisture that accumulates 
on either side of your windows (whether exterior or interior sources) and 
leaks down through the window into the wall is led all the way to the 
outside of your wall - I mean complete pan flashing under windows that 
are exposed to rain or in very cold climates where there might be a lot 
of condensation in the winter and sloped sills that extend beyond the 
wall with drip edges etc.

The goal is to keep as much moisture out as you can without jeopardizing 
the other goal of making sure the moisture that does get in can get out. 
The drier the climate the less rigor is required to a point. SB buildings 
in Tucson have had major moisture problems and needed to have the bales 
replaced - I can think of three without trying - you can get away with a 
lot in the sahara or death valley but otherwise you need to pay attention 
to these things.

Got to go...

David Eisenberg -  on a sustainability and codes odyssey in the Pacific 
NW - Portland, Eugene, and today - Olympia, tomorrow Seattle/King County, 
Wednesday Ellensburg, Thursday Spokane, then back to Portland for the 
final weekend of the Village Building Convergence (check out 
www.cityrepair.org - awesome!)

David Eisenberg, Director
Development Center for Appropriate Technology
P.O. Box 27513, Tucson, AZ  85713
(520) 624-6628 voice / (520) 798-3701 fax

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