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Re: GSBN:Fwd: CASBA_ Pea Gravel

David, Mark, Chris, et. al. - My viewpoint has always been that this
is mostly an issue of separation from rising damp and condensation,
though it appears the code section was not written in such a way...
Building in Arizona (yes, I know, we get away with everything here...
at least climatically speaking), we have never been overly concerned
about moisture "coming down inside the walls", but have had occasion
(on flood-irrigated lots, mostly... don't ask, you'd be appalled...)
where a slab might get saturated over a short period of time.

First, a bit of support for the drainage mat/board idea...

The retaining wall drainage mat/board has many advantages... As we
all know, the boards intentional use is to take away the "hydrostatic
pressure" at the moisture/vapor barrier on the backside of a
retaining wall.  Most  accomplish this by allowing moisture to pass
through their "earth-side" face, and then allow it to "fall through"
them in their vertical orientation, while some type of nominal
moisture/vapor barrier on the "wall-side" keeps the moisture from
passing all the way through (a la Roxul's product).  The other major
challenge they have to meet is not being crushed by the mass of earth
behind the retaining wall, to the point where they can no longer
drain, and so they have an internal rigidity that doesn't, at the
same time, defeat the drainage capability.  I think this situation is
not dissimilar to the conditions at the bottom of a bale wall
(especially a load-bearing one...), where the downward pressure of
the bales has to be supported between the sill-plates, and, if sloped
a small amount, the drainage board can let moisture into it's upper
surface and drain it out along it's lower surface.

But now for the "killer app" idea...

Chris' recalling of his "shredded" food containers made me think of a
similar, perhaps more widely available, alternative... All those
billions of "packing peanuts" that seem to be such a scourge to
landfills and recyclers alike.  Typically, these are "extruded"
polystyrene (XPS), and so are in theory impervious to water.  But,
poured into the space between sills, they would provide the perfect
open "drainage plane", would be highly insulative, and also be well
able to resist the pressure of the bales above.  Now, the only
caution is to make sure your "recovered" packing peanuts are all
petro-plastic based.  Because of the push of those "green meanies"
(is that what they call us?), more and more of these peanuts are
bio-based plastics which will bio-degrade, or even melt in your mouth.

So, who would have thought one of the stars of bad environmental
practice, the plastic-foam packing peanut, might come to the rescue
of a star of the natural building movement, straw-bale.

Just a thought...
Tom Hahn

I love it when we get all fired up on these detail questions.

What to do in the sills has always been a concern of mine. Somebody
mentioned Roxul drainboard, which is what I used to use until it was
pointed out to me that it only drains when placed vertically. In a
horizontal application, it holds water really really well.

This year, I used two different materials that I really liked. David
mentioned that foam, while not always the most desirable product, has
qualities that suit this application. I saved up foam meat and
vegetable trays from home last winter, and then had enough to crumble
up and fill the sills for half of a large building. Not always do-
able, I agree, but it was free, provided insulation, but not that
solid foam "barrier" for those who worry about having some drainage.

The more practical material I used this year was zebra mussel shells.
I was impressed with the use of big mussel shells in Denmark. We
don't have them here, but we do have big troubles with invasive zebra
mussels, and their shells made a very good fill in the sills. Enough
trapped air to be decent insulation (better than pea gravel or sand),
but enough space to drain a bit of moisture and they won't allow any

Of course, no code would have crumbled meat trays or zebra mussel
shells written in. But when I explained to the building official what
the intent was, he was quite amenable to both materials.

In terms of using that space for "drainage" I do embed those little
brick drains about every 4-8 feet on the exterior sill. Basically I
put one in where I have a joint between pieces of wood for the sill.
I've never seen or heard of anything weeping out of these, and don't
know how effective they would actually be for various amounts of
water, but for a couple of bucks I've been doing it just to feel better.

As an "aside" to this sill plate discussion, I have been tending
toward using foundation systems that are not monolithic under the
bales, i.e., two rows of earthbags or two rows of narrow concrete
blocks on a rubble trench or on a poured concrete footing. This
leaves between 4-12 inches of space in the centre of the wall
(depending on the material I'm using and bale size/orientation). This
wider space makes for great insulation without having to resort to
foam on the exterior of the foundation, and plenty of drainage should
that ever be necessary. Less concrete, too.

Thanks all for pitching in to these great discussions.


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