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Re: GSBN:Fwd: CASBA_ Pea Gravel
We've supported the use of pea-gravel or some other broken plane, not
because we think the wall will be drenched with water, but based on our
observation of vapor migration and accumulation through bales. Here's our
- Vapor is continually moving around inside a bale wall as temperature
conditions change. Many observations have been made of considerable diurnal
movement of moisture within a bale wall, and significant differentials in
humidity between the top and bottoms of a wall.
- It's easily observed that as moisture migrates through a bale it is
prone to stop and accumulate at any impermeable surface, and reach a
concentration where rotting will occur. This is why we avoid vapor barriers
on the bale sides. The same conditions can occur at the tops and bottoms of
- Bear in mind, also that the sills are at the bottom of the wall
where the most wetting occurs from direct rain and rain splash from the
ground. Some of this moisture will initially migrate to the bottom of the
wall by gravity, especially in conditions of cold rain. As David Arkin is
wont to say, good boots, good hat, etc.
- Some moisture may come from the footings: even though there might be
some vapor barrier in place, it is often imperfect due to foundation design
- Leaks do occur around windows and cracks, and gravel does provide a
path for dissipating moisture.
- Accumulated rot in one place, the bottom of the bales, could
compromise the integrity of the wall.
I understand that many of us are very, ah, fixated, on R-values and
buttoning up our coats. I would not trade increased insulation for
cautious vapor management. We typically use two 4x plates of wood, which is
good for at least R-10---slightly low but not so far from optimal for
horizontal insulation when located low in the building shell, in our
climate. We have also used, in colder climates, a scheme we learned from
Ken and Polly, simply alternating strips of rigid insulation with channels
of pea gravel, so you can get another 4-5" of rigid down there and make Al
Gore a little happier...
John "Gore-Techs" Swearingen
On Dec 11, 2007 9:37 PM, Jeff Ruppert jeff@... wrote:
> David and Anni (or Catherine et al),
> I completely agree with your questioning of this requirement. In our dry
> environment, we use all sorts of materials between the sills, with fine
> IMHO, this brings up the ever-present issues related to what we codify.
> Any mention of specific materials makes things like this prescriptive,
> not open to performance qualifications, nor the ability to prove intent,
> since no accompanying explanation of intent is present. Any future
> attempts to codify bale construction techniques should have accompanying
> intentions. There are too many environments and situations that will
> arise conflicting with any codification of our work.
> The recent work by Martin Hammer and everyone else in the past has been
> wonderful, but I really think we can do better and qualify our intent,
> just as other parts of the code include. There are accompanying text of
> intent for code structures in Canada (B.C.) and whole sections of the
> I.B.C. that have intent documents.
> Anything we do with regards to codes will serve us better by including
> our intentions so those of us in questionable circumstances can benefit
> from any contributing work in these areas.
> Catherine Wanek wrote:
> > I am forwarding this inquiry from the California Straw Building
> > Association (CASBA) list from award-winning architects David Arkin &
> > Anni Tilt. Perhaps this will stimulate discussion on the GSBN e-waves.
> > -Cat
> >> From: "David Arkin, AIA" david@...
> >> Date: Tue, 11 Dec 2007 17:21:39 -0800
> >> Subject: CASBA_Mem Pea Gravel
> >> Fellow CASBAnauts (CASBAnuts?):
> >> We haven't used pea gravel between our sill plates for some time now,
> >> using rigid insulation instead. My opinion is that if a bale wall has
> >> enough water in it to need 'drainage' (from any source), those bales
> >> are goners.
> >> The building official in Sonoma is citing it's recommendation in
> >> SB332 as a good enough reason to require that it be there. SB332
> >> says, "There shall also be a drainage plane between the straw and the
> >> top of the foundation, such as a one inch layer of pea gravel." Does
> >> anyone know of the intent of this?
> >> More importantly, does anyone know of any testing as to why this
> >> might (or might not) be a good idea?
> >> Your thoughts (and/or Holiday Greetings) always appreciated,
> >> David and Anni
> >> * * * * *
> >> Arkin Tilt Architects
> >> Ecological Planning & Design
> >> David Arkin, AIA, Architect
> >> LEED Accredited Professional
> >> CA #C22459/NV #5030
> >> 1101 8th St. #180, Berkeley, CA 94710
> >> 510/528-9830
> >> www.arkintilt.com
> >> "There is no way to peace. Peace is the way."
> >> Ñ A. J. Muste
> >> -
> >> Use REPLY to respond to the sender only or
> >> use REPLY ALL to respond to the entire list.
> >> CASBA Website can be found at <a target="_blank" href="http://www.strawbuilding.org">http://www.strawbuilding.org</a>
> > ----
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> > list, send email to GSBN@...HELP in the
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Skillful Means, Inc.
Design and Construction
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