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Re: GSBN:Fwd: CASBA_ Pea Gravel

As long as we're going to full bandwidth on this, let's get into the issue
of drainage plain vs moisture barrier, and the subject of detailing,
something that DE touches on, but doesn't resolve.  As he said, it could be
an issue with our beloved Sonoma County building department, which often had
creative interpretations of code issues.

The moisture barrier part...checking rising damp, is straightforward. There
are two approaches, the capillary break (pea gravel) and the moisture
barrier (tar, paper, bituthane).  We use both--a moisture barrier under pea
gravel.  We prefer a liquid-applied "tar" because typically this is an area
that wasn't covered by the plastic vapor barrier that went under the slab.
It's a low tech and high tolerance issue--ie it doesn't have to be done to

"Drainage plane" is, to me at least, a confusing term, and seems to imply
that there's a bunch of water to be drained.  Usually, a drainage plane is
designed to keep water from getting deeper into the building envelope, as
with a rain screen, or a drainage mat under a roof.

In this case, though, if the "drainage plane" is seeing any water, the game
is already over--moisture has come from higher up the wall, and I guess it's
purpose is to keep the foundation from getting wet?  Help me on this one!

And a note on detailing:  if it's not detailed to drain properly, this
"drainage plane" is actually more properly called a "moisture collection
basin", or MCB.  And if the purpose is to drain the wall, where are you
draining it to, and how does that help your building?

The question I've been asking recently is:  If your walls are getting so wet
that the gravel is taking on water, wouldn't you want to know about it?  I
mean, some damage is very likely occurring, and the sooner you find out the
less damage there will be.

We have previously detailed walls to discretely deposit their moisture to
the outside, thereby saving expensive insurance claims for varnished floors
and mold in the walls. A few months ago, Dan, Dietmar and I examined an
owner-built building that had extensive leakage through cracks on the
rain-exposed side of the building at the second floor.  The owners
eventually noticed the problem on the ground floor when water puddled after
large storms. . In the meantime, the plywood box beam above was already
seriously rotted.

This caused me to think...hmmm, if that water were going somewhere that the
occupants would have noticed earlier, the problem could have been nipped in
the bud.  What is the down side of detailing so that the MCB drains only to
the inside?


Oh, yeah....  What does David Arkin tell the building department?  I think
two of the suggestions so far would work...(1) alternating strips of
insulation and gravel, (2) insulation below gravel.  I wouldn't favor
David's suggestion of (3) insulation on one side, gravel on the other,
because of the issue of putting bales on an impermeable surface.

John "What's that funny Smell?  Swearingen

On Dec 12, 2007 10:51 AM, David Eisenberg strawnet@... wrote:

> Hi all,
> There are several excellent points already made here:
> - that prescriptive requirements, whatever they might be, are typically
> limiting and not always appropriate, especially in the hands of
> designers or code officials with limited understanding of particular
> systems, materials or methods of construction,
> - that in this case, we actually don't have research and testing
> results to rely on for this,
> - that there are a number of competing concerns wanting to be addressed
> and probably an even greater number of theories and strategies
> competing to meet them,
> - that including intent is critically important in writing codes,
> though missing more often than not in most codes (this should not be a
> deterrent to us getting it right going forward),
> - that there are at least a couple of methods (with some variations)
> that predominate now - pea gravel or something equivalent and rigid
> foam insulation,
> - and of course, there is the first point, that David Arkin and company
> have a particular problem at present and have asked for some help...
> The language "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."
>  The question of intent is a complex one, and I can only say that that
> was not language that I would have used - in part because it isn't
> correct - this is not a drainage plane, but more accurately would have
> to be called a drainage zone - that is, a separation between the straw
> and the top of foundation.
> The question is what to do about this - how to provide information that
> would both help with David's problem and guide us in the next evolution
> of codes.
> Over the years I've gone back and forth a good bit on how best to
> address this issue. John makes the point that moisture moves around
> inside assemblies both as water vapor and liquid water (hopefully the
> latter only rarely and in very limited amounts - though enough water
> vapor in the presence of cold-enough condensing surfaces can produce
> plenty of liquid water). Not included in what follows are the other
> environmental issues surrounding the use of foam and various other
> moisture barriers and so forth. Figuring out what's going on with
> moisture and how to most effectively deal with it is what I'm focusing
> on, but I don't discount in any way the importance of being conscious
> of what we're using to achieve those goals and what their impacts are.
> I just don't have time or space to go into all of that now. In general
> I tend to favor the lowest tech, lowest impact EFFECTIVE strategies,
> thinking about what else might be at stake if what you're focused on
> fails to perform as required.
> Here are the concerns/issues that I have thought most about...
> *First and most obviously, we've always thought it important to raise
> the bales above the floor level (for either slab-on-grade or top of
> foundations that are at the same elevation as the floor) or where
> exterior slabs or floors are at the same elevation (such as porche
> slabs - we've seen porch slabs which sloped back toward the house with
> bales sitting on a moisture barrier at floor level - why did we see
> this? Because we were called to help remediate the resulting rot at the
> bottom of the wall as the bales got wet every time it rained). This is
> both to keep the bottom bales dry during construction and to deal with
> plumbing disasters, overflowing bathtubs or toilets, etc. but also has
> the benefit of providing structural attachment of netting or mesh,
> tie-downs, etc. and solid backing for plaster grounds, mesh, and
> flashing on the exterior and plaster grounds and baseboard trim on the
> interior.
> *Rising damp (terminology from the UK, which I think is perfect because
> it describes what is going on with soil moisture coming up into
> buildings and assemblies by both capillary action and the movement of
> water vapor), which necessitates the inclusion of moisture barrier of
> some sort at the top of the foundation or on the slab (in the case of
> slab-on-grade construction). This deals with moisture coming up into
> the wall assembly.
> *Condensation caused by cold foundations or slabs. This is what led to
> the two current practices of either having pea gravel or foam between
> the sill plates or whatever method is used to raise the bales above the
> floor or foundation. I have a basic preference for foam insulation for
> the energy conservation benefits and for separating the bales from a
> cold condensing surface. But along with these benefits come the issues
> the John raised concerning having an impervious material against the
> straw. So if liquid water is in the wall and gets down to the bottom of
> the wall, it could sit on this foam as liquid and cause problems. I
> know that some people have devised a way to cut sloping slots in the
> foam every few inches so that any significant amount of liquid water
> would drain toward the exterior plaster where it could get out or have
> some chance to dry. The idea of the pea gravel was to have support for
> the bale without creating a surface for water to collect on at the bale
> interface and to also have a capillary break to keep water that might
> accumulate at the top of foundation level (on top of the moisture
> barrier) from wicking up and wetting the straw. And of course this also
> allows more movement of water vapor in the entire assembly - which is
> either good or bad depending on how much and where the moisture is
> coming from and where it's going.
> *Desire to have adequate strength for seismic areas and height of
> elevation above top of foundation/floor level has led to the use of
> 4x4s (roughly 3-1/2" x 3-1/2" or 89 x 89 mm) for sill plates to the
> interior and exterior edges of the bales. This actually allows for
> different strategies, including, if one wanted to do so, a combination
> of foam at the bottom and gravel on top of the foam. This could be
> further refined to have the foam insulation fill the full height of the
> sill plates for the inner half of the space between the plates and the
> pea gravel fill the upper space on the exterior side. You could put a
> layer of 2" thick insulation across the whole space at the bottom and
> then a second piece of 1-1/2" thick insulation on the interior half of
> the space, filling the rest with pea gravel. This would give you pea
> gravel for drainage where it's most likely that liquid water would
> occur while providing good insulation to the overall assembly.
> And obviously, there's are many other possible strategies and
> materials. Years ago I suggested using a clay-based oil absorbent
> material (it's the same as kitty litter - the stuff used in cat boxes,
> only you can get it in much larger, less expensive quantities) instead
> of pea gravel as the fill between sill plates since it has the capacity
> to absorb and chemically bind a fair amount of water. Of course at some
> point it would reach its capacity to hold moisture and they be much
> like other fillers.
> Perhaps the design I suggested above - with the combination of foam and
> pea gravel would satisfy the building official. Eventually we'll need
> to get this sorted out.
> That's my two and a half cents for today...
> David Eisenberg
> -----Original Message-----
> From: John Swearingen < john.skillfulmeans@gmail.com>
> To: GSBN GSBN@...; david@...
> Sent: Wed, 12 Dec 2007 9:10 am
> Subject: 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
> reasoning:
>    - 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
>   a wall.
>   - 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
>   and execution.
>    - 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
> > results.
> >
> > 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.
> >
> > Jeff
> >
> >
> > Catherine Wanek wrote:
> > > I am forwarding this inquiry from the California Straw Building
> > > Association (CASBA) list from award-winning architects David Arkin &amp;
> > > 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 &amp; 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."
> > >> &#xD1; A. J. Muste
> ________________________________________________________________________
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John Swearingen
Skillful Means, Inc.
Design and Construction

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