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GSBN: Digest for 5/12/05
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- Subject: GSBN: Digest for 5/12/05
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- Date: Thu, 12 May 2005 23:29:44 -0500
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-> More moisture problems - Southern California
by "Bob Bolles" Bob@...
Date: 12 May 2005 13:09:01 -0600
From: "Bob Bolles" Bob@...
Subject: More moisture problems - Southern California
Good day all,
Sorry for some cross-posting to a couple of other lists.
Like the Straw Wolf and Danny Buck, we have a real problem with "moisture" in
the walls of a project in our area. No, it isn't one of mine, but it is this
kind of "problem" that can give Straw Bale Construction a bad name, so it is
I do remember the exchanges regarding the SB that Danny was working on, but
was kicking myself because I hadn't saved them - Thank you Joyce for
"reminding" me that it had been reprinted in issue #49 of TLS, and thank you
all for your extremely valuable insight and sharing your experiences. If we
can actually root out the sources of the moisture, and come to some
conclusions, I hope to be able to write some sort of analysis and summary for
future reference. I think your past and future input on the subject will be
This is a large home (3,000 Sf) with lots of amenities, and the parapet style
is consistent with other projects by the same Architect.
This year was one of those few "wet" years that we have, and in the area of
the project, (Ramona, San Diego County, CA - USA) the rainfall for the season
was ~25 inches; the 2nd highest on record. Some of the rains were very heavy
downpours and much of those were wind-driven directly into the South and
West-facing parapet walls.
Several items of particular note: Water was detected dripping out of the
kitchen soffit after only 1-1/2 days of rain, and moisture content readings,
principally grouped in 6 different locations, were recorded at +- 40% within
the center of the bales. Other reading surrounding the affected areas ranged
between 15 and 20%. While the current readings indicate some areas were wetter
than others, I believe (speculating) that the leakage occurred pretty much all
along the parapet walls on the South and West sides of the house. There were
wet walls elsewhere, but perhaps they were caused by different problems. The
architect just reminded me that there were also quite a few wet spots in the
wood-framed portions of the home, which makes this even more interesting.
All window and door opening were sealed with bituminous material between the
openings and the frames. I have been told that a moisture barrier was used to
cover the wooden parapets and lapped over the bales.
The plaster was a 3-coat cement stucco - I am still investigating whether lime
was used in the mix, but it seems unlikely. It seems more probable that the
plaster was more of a moisture barrier than a likely source as the point of
water entry. No sealer was applied to the stucco. There is some cracking, both
horizontal and vertical, and while a few are potentially large enough to allow
water into the bale interior, at best they could only account for some of the
water at some locations. There are also hairline cracks; and I guess the
thinking is that the rainfall may have penetrated all 3 plaster layers.
The framing details on the plans don't really tell me a lot about the
construction of the parapet, other than it seems to be an extensions of the
posts, and I am assuming that it was sheathed, papered, lathed and plastered.
The roofing detail sheet is a cookie-cutter and doesn't even illustrate a
parapet of this type.
I have compared notes with Mark Tighe, another experienced bale builder and
who also examined the house - each of our independent investigations lasted
about 3 hours. We both came to pretty much the same conclusion that nothing
that we could see would account for all of the water that appears to have
entered the wall up around the (wooden) parapet extension. There was at least
some penetration there because there were consistent wet readings all along
the top of the walls at the ceiling. We can't tell how much entered there or
how much may have entered down the wall.
It has been suggested that where the first water was spotted, one potential
scenario is that water penetrated the stucco (from where is yet unknown) and
ran down the inside face of the interior plaster until it hit the box beam
kitchen soffit, where it poured into the soffit and out the light fixture.
This might account for the kitchen leak, but in the few plastered test walls
that I have (struggled to) removed the plaster from, there wasn't what you
would call a lot of room for water to travel through very rapidly. Also, how
would the water get to the interior plaster surface? Water doesn't flow very
well across bales.
To make this all a bit more interesting, the owner has grasped onto the idea
of installing a sheet moisture barrier between the plaster and the bales when
the time for repair comes (not that I blame him at this point). I and others
(and he has read) have explained that this is likely to cause moisture to be
trapped within the cavity and in itself cause rot. He said that he had heard
that, but has yet to see evidence that is really true. Not that is shakes my
faith in the truth of the supposition, come to think of it, other than from
the Straw Wolf, neither have I, though John Straube has published some very
convincing test data that certainly makes the case.
My next step is to contact the contractor, that is now out of state, and see
if they can give some insight as to the potential failures. I have requested
that the owners create a grid of test holes from the inside, where the others
are, and really see if we can figure out just where and how widespread the
problem really is.
I feel for these folks, fearing the worst (whatever that is) and about to
watch parts of their house being demolished. Not happy campers and I know that
everyone feels badly.
I would appreciate hearing your thoughts on the subject.
At the moment, the owners are pretty upset that they are in this position, and
are now questioning anyone's point of view unless there is documented evidence
to back the assertions up. I can't fault them for that.
Their questions are as follows - please do what you can to provide some sort
of documentation and/or experiences supporting your thoughts.
1) Do parapet walls "always" allow moisture penetration? Any experiences or
testing that might indicate why some did and others didn't?
2) Does 3-coat cement plaster (stucco) allow enough water to penetrate a wall
and substantially "soak" the bales? I seem to recall that Dr. Straube's tests
involved capillary uptake, but I don't think that if I had the rest results in
front of me I would necessarily understand them without a really clear
explanation. How would this compare to rainfall on a vertical wall surface?
3) Will a sheet moisture barrier between the bales and the plaster cause the
bales to decompose?
4) Will a non permeable stucco function the same as a sheet moisture barrier
and cause the bales to decompose?
5) Is there any rule of thumb that would give us an indication that over that
moisture content % the bales won't likely dry out, but under that % they will
likely dry out. I understand that is a "difficult" question because much will
depend on the drying conditions, but I was wondering if someone had reached
some conclusion made from personal observation in their experiences.
I will pass on any developments as I can.
My thanks in advance for any insight, experiences, information on other
failures and documentation of the causes. If at all possible, I am in hopes
that we will be able to pass on any information that will assist those in the
future make "better" and informed decisions.
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