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<div class="moz-cite-prefix">Thanks John and Graeme for the
replies. They validate my thinking on this, I'm glad to hear I'm
not over-trivializing the issue. That said, I'm hoping to drudge
up something more specific to have a well-informed (i.e. case
studies, test data, modeling) response to the performance
consultant's concerns. I think his concerns are valid, but
overblown, fueled primarily by a lack of familiarity with how
these systems work (possibly mixed with a fear of the dreaded
solar vapor drive that has sunk well-publicized brick-clad, vinyl
wall-papered development houses). That said, in the language of
data, and with my climate outsider status, I'll need a bit more to
convince him than theory - despite how convincing it is.<br>
<br>
This is exactly why I'm developing the in-wall temp/RH sensor
systems (not sure if I mentioned these yet on this list? I've
spoken with at least a few of you about this). Having access to
long-term data from real buildings in a variety of climates will
really help inform these types of conversations. I'mabout to
deploy the alpha-beta version, will be asking for interested beta
testers in another month or so, more to come...be in touch if you
are interested in putting sensors in your bale walls...<br>
<br>
Thanks, glad to be a part of this group!<br>
<br>
Jacob<br>
<br>
<pre class="moz-signature" cols="72">Jacob Deva Racusin
New Frameworks Natural Building, LLC
P.O. Box 15, Montgomery, VT 05470
(802) 782-7783 (c)
(802) 326-2209 (h)
<a class="moz-txt-link-abbreviated" href="http://www.newframeworks.com">www.newframeworks.com</a>
<a class="moz-txt-link-abbreviated" href="mailto:jacob@newframeworks.com">jacob@newframeworks.com</a></pre>
On 5/28/2013 6:22 PM, Graeme North wrote:<br>
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hi Jacob
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<div>The approach I have favoured where we can get days of wind
driven rain and very high humidities is to keep by far the
majority of the water off the walls either with exterior
rain-screening or very good eave protection. If the exterior
pastors can not get saturated then the other issues that concern
are not likely to follow.</div>
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<div>This approach works a treat for me and I get to sleep at
night.</div>
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<div>cheers</div>
<div><br>
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<div style="font-size: 12px; ">Graeme</div>
<div style="font-size: 12px; "><br>
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<div style="font-size: 12px; ">Graeme North FNZIA</div>
<div style="font-size: 12px; ">Graeme North Architects</div>
<div style="font-size: 12px; ">49 Matthew Road</div>
<div style="font-size: 12px; ">RD1</div>
<div style="font-size: 12px; ">Warkworth 0981</div>
<div style="font-size: 12px; "><br>
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<div style="font-size: 12px; "><a moz-do-not-send="true"
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<div>On 29/05/2013, at 3:01 AM, Jacob Deva Racusin <<a
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href="mailto:buildnatural@googlemail.com">buildnatural@googlemail.com</a>>
wrote:<br>
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<blockquote type="cite">Greetings,<br>
<br>
I am working with a client in the mid-Atlantic region of the
United States (southern Maryland), and a concern has come up
regarding inward vapor drive of a plastered wall. In this
case, the insulation is dense-packed cellulose, but may as
well be straw for all practical purposes of this
conversation. Exterior lime-stabilized base plaster with a
finish lime plaster is designed to be directly coupled to
the insulation, using traditional wood lath as a substrate.
The concern is that a moisture-charged reservoir of plaster
directly adjacent to the insulation will result in a strong
inward vapor drive during wetting events followed by sun
(solar vapor drive), on top of what is already a
inward-dominant vapor drive for that climate (despite the
fact that it is a heating-dominant climate - this is what
the local performance consultant tells me). We discussed
the application of limewash or silane/siloxane to reduce
liquid absorption into the plaster, as well as the creation
of a vapor-open assembly allowing the vapor to drive all the
way to the interior and the use of clay plaster to store
excess moisture. This building will be relatively tight
with adequate ventilation. That said, the local performance
consultant is very concerned about the assembly's ability to
deal with inward vapor drive and the lack of drying
potential in that climate. For reference, I practice in the
relatively colder Northeast. To that end I'm looking for
advice on a few things:<br>
<br>
- Do any of you have case studies and/or hygrothermic models
(i.e. WUFI) of plastered exterior systems in humid
mid-Atlantic climates? By 'case studies', ideally some
degree of moisture testing would be helpful for convincing
the skeptical, but basic empirical "this is working under
these conditions" would be great too. The performance
consultant is going to run a model through WUFI Passive, but
I'd be interested in seeing if anyone has already looked at
this, particularly for this climate.<br>
- Has anyone seen failures in plastered exterior systems as
a result of vapor migration? Not from liquid, mind you - or
rather, not bulk liquid penetration through the plaster into
the straw (or cell, in this case) - but from condensation or
significantly-elevated RH?<br>
- One recommendation is to back-vent the plaster. I fully
understand the benefit of this in regards to interrupting
vapor drive and allowing penetrating liquid to drain, and
the air-seal would then be provided by an exterior air
barrier/weather-resistant barrier on the inward side of the
gap. All other considerations of feasibility and cost
aside, I'm concerned about saturation of the plaster and a
greater propensity for damage from freeze/thaw conditions
with atmospheric temps being able to reach both sides of the
plaster. Any reason I shouldn't be concerned about this?
Any recommendations on appropriate detailing for
back-venting a clay plaster? I'm inclined to use wood lath
as a substrate, but wonder if this would only exacerbate
damage from freeze/thaw...<br>
<br>
Thanks in advance for your insights,<br>
<br>
Jacob<br>
<br>
-- <br>
Jacob Deva Racusin<br>
New Frameworks Natural Building, LLC<br>
P.O. Box 15, Montgomery, VT 05470<br>
(802) 782-7783 (c)<br>
(802) 326-2209 (h)<br>
<a moz-do-not-send="true"
href="http://www.newframeworks.com">www.newframeworks.com</a><br>
<a class="moz-txt-link-abbreviated" href="mailto:jacob@newframeworks.com">jacob@newframeworks.com</a><br>
<br>
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