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Martin,<br>
<br>
We've had a lot of snow pack up against our buildings. I have
noticed that in some places - particularly against north walls where
it takes a really long time to melt - premature wear against the
plaster can be an issue. This is common enough to encourage us to
provide generous overhangs (24" min) and really strong separation of
exterior plaster from grade (18-24" standard) as standard practice,
although honestly that's as much to address splash back as snow
pack. I have also noticed, however, that there is enough heat loss
from the walls to melt the snow directly adjacent to the wall -
there is almost always a gap between the exterior wall surface and
the snow bank, and that's obviously helpful. The drying potential
of the plaster in this region, from our limited but relevant testing
in late winter/early spring during our testing program, seems to be
adequate in nearly all cases, with higher MC% against the north wall
where the drying potential in general is worse. Not sure that
counts as a formal answer, but our general strategy as been to get
the plaster/bale assemblies up above most of the snow back, and not
worry to much about it when the snow does build up. It's been
working pretty well so far, to the best of our knowledge and
testing.<br>
<br>
In a related note, I've just been consulting with a contractor
working on a wood-clad straw wall up here, who is dealing with
premature failure of a skirt board against the inside corner of a
bump-out on a north wall. The leading hypothesis, after consulting
a lot of pretty smart folks (including Derek Roff, on this list), is
that the combination of snow pack and drip line from an
inadequately-flashed bump-out roof is causing dramatic splash back
at that location. So, snow isn't just an issue of melting water, it
also changes the grade profile during that magic window where it is
raining/roof snow pack is melting and the snow banks are still
there. Apparently, if the theory is correct, this can foil some
otherwise-adequate bottom-of-wall detailing strategies. And if it
can rot out wood in three years, plaster stands little chance...<br>
<br>
My apologies to the metric-oriented members of the community, I am
thoroughly illiterate in that regard.<br>
<br>
Cheers,<br>
Jacob<br>
<br>
<div class="moz-cite-prefix">On 7/11/14, 7:57 PM, martin hammer
wrote:<br>
</div>
<blockquote cite="mid:CFE5C7FF.1AD7C%25mfhammer@pacbell.net"
type="cite">
<title>Re: [GSBN] Straw bale at high altitudes (and snow against
bale walls)</title>
<font face="Arial"><span style="font-size:9pt">Hi Misha,<br>
<br>
In terms of moisture concerns for strawbale walls, elevation
in itself is not relevant. What matters is climate
(precipitation, temperature, humidity, wind), and how it
relates to interior “climate”. Higher elevations do mean
lower relative temperatures for the region (in all seasons,
3-5 degrees F per 1000’), so indirectly it matters. But very
low outdoor temperatures <u>beg</u> for strawbale walls (just
ask our Canadian friends!). As long as you employ normal good
practices to prevent relatively warm-moist interior air from
condensing in the strawbale wall, by using a vapor retarder on
the inside face of exterior walls (the IRC requires Class III
vapor retarder (between 1.0 and 10 perms) in cold climate
zones) and by sealing penetrations on the inside face of these
walls.<br>
<br>
I agree with what everyone else has said re: the foundation
issues.<br>
<br>
Also the concern was raised about snow sitting against the
bale walls. I’ve never been convinced one way or the other
whether this is a real or an imagined problem. Thoughts /
questions include: <br>
<br>
</span></font>
<ul>
<li><font face="Arial"><span style="font-size:9pt">When the
snow-wall interface is below freezing, presumably nothing
detrimental occurs.
</span></font></li>
<li><font face="Arial"><span style="font-size:9pt">When snow at
the snow-wall interface melts (because all snow is melting
or because the snow at the interface melts because the
wall surface is warm enough) is a space created that
allows drying of the plaster, and thus no harm? </span></font></li>
<li><font face="Arial"><span style="font-size:9pt">When the snow
at the snow-wall interface melts, does it saturate the
plaster, which then wets adjacent straw causing
degradation, and/or does moisture in the plaster sometimes
freeze and damage the plaster?<br>
</span></font></li>
</ul>
<font face="Arial"><span style="font-size:9pt"><br>
Does anyone have experience with snow against bales walls that
answers these questions?<br>
<br>
Thanks<br>
<br>
Martin <br>
<br>
</span><span style="font-size:8pt"><b><i>Martin Hammer,
Architect<br>
</i></b>1348 Hopkins St.<br>
</span><span style="font-size:7pt">Berkeley, CA 94702<br>
510-525-0525 (office)<br>
510-684-4488 (cell)<br>
</span><span style="font-size:9pt"><br>
<br>
On 7/11/14 8:40 AM, "Misha Rauchwerger" <<a
moz-do-not-send="true" href="misha.rauchwerger@gmail.com">misha.rauchwerger@gmail.com</a>>
wrote:<br>
<br>
</span></font>
<blockquote><font face="Arial"><span style="font-size:9pt">I have
a client that wants to build a straw bale house at 4000 feet
in the Sierra Foothills. They have been getting conflicting
information about the wisdom of building with straw at that
elevation. In particular there is the concern about the
effects of moisture in the wetter months, and possible
condensation inside the walls. They know about the need for
big eaves, and permeable plasters, but have been swayed
against the idea from a local green architect in town.
Please direct me to any research, or anecdotal evidence to
support straw bale construction under these conditions, or
maybe there is valid concern. I have only built in the
lower/dryer elevations on flatter sites.<br>
<br>
They also share these concerns:<br>
<br>
Their lot is sloped, so they would likely have to build a
full walk-out basement on the lower level, and the living
space on the upper level. This means that the full lower
level is built of concrete (probably Faswall or Durisol);
will they would have to build out the lower walls to match
the width of the straw bales? How is this disparity in wall
thicknesses usually resolved with the least cost/impact?<br>
<br>
- With a walk-out basement, is it possible/reasonable to do
a stepped-foundation on the lower level to minimize the
amount of concrete used? Or does the mixed use of concrete
and post/beam and straw bale construction create
unreasonable headaches in the building process?<br>
<br>
Thanks everyone for your comments,<br>
Misha Rauchwerger<br>
builtinbliss.com <<a moz-do-not-send="true"
href="http://builtinbliss.com">http://builtinbliss.com</a>>
<br>
<br>
<br>
<br>
<br>
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<br>
<div class="moz-signature">-- <br>
Jacob Deva Racusin <br>
Co-Owner<br>
New Frameworks Natural Design/Build<br>
<br>
Author, The Natural Building Companion<br>
Chelsea Green Press, 2012<br>
<br>
(802) 782-7783<br>
<a class="moz-txt-link-abbreviated" href="mailto:jacob@newframeworks.com">jacob@newframeworks.com</a><br>
<a class="moz-txt-link-freetext" href="http://www.newframeworks.com">http://www.newframeworks.com</a></div>
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