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Re: GSBN:More moisture problems - Southern California


We have been dealing with some moisture issues lately as well, which
are not as dramatic as yours, but are troubling nonetheless.  I'm
gathering data at the moment and will be writing to the list before
too long.  This is all a sign that straw bale construction is growing
up, though I agree that it's very hard for the people on whom the
problems land.

I don't have any documetable answers to any of your questions, but I
do have another question for you.  You said:
" +- 40% within the center of the bales. Other reading surrounding
the affected areas ranged between 15 and 20%. "  It would seem
important to look at the moisture levels at the interior and exterior
of the walls in these areas where the center was so wet.  Maybe you
have done this, but it's not clear from the language in your posting.
My experience has been that wetness from rain on the wall surface (or
even potential wetness from rain- in our climate it can be difficult
to separate rain from condensation as sources) does not penetrate
more than an inch or two into the bale.  It is difficult to imagine
rainwater making its way to the center of the bale wall, unless
through a leak.  And it's nearly impossible to imagine it making its
way to the interior.  It may be possible in the 15-20% regions to
document some pattern of striation through the wall section- is it
consistently wettest toward the interior, middle, or exterior?  In
any situation that is only an exaggeration of the normal conditions-
like lots of rain against the wall surface, instead of the normal
amounts, you would be able to pick out a pattern of dampness that was
an exaggeration of a normal pattern- wetter toward the outside, dryer
as you move in.  If this is not the case, it would seem that the
water is coming from somewhere else- like a roof leak.  This could be
useful in convincing the owner.

To get closer to an answer to your last question, while also giving
the owner something constructive to focus on,  I'm wondering whether
you can find an isolated section of wall on which to conduct an
accelerated drying experiment.  You could apply heat to the interior
face (maybe an electric blanket against the wall with a couple of
regular blankets behind it?) and then consistently test moisture
content from the outside.  If you cover your holes well (duct tape
seems to work) you should be able to re-use them without throwing off
your readings.  If you drill the holes a bit oversized, in successive
readings you can change the angle of the probe, to go into fresh
straw.  You might also put a thermometer behind the blanket at the
interior wall surface, and chart the temperature there. A max-min
thermometer could be helpful, though I would think the termperature
would remain pretty consistent.  Then a person who is adept with
these types of numbers might be able to extrapolate your readings to
guess at a drying rate under more normal temperatures.

Best of luck and please keep us updated on your progress.


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 everyone's problem.

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 invaluable.

This is a large home (3,000 Sf) with lots of amenities, and the
parapet style is consistent with other projects by the same

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

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

1) Do parapet walls "always" allow moisture penetration? Any
experiences or testing that might indicate why some did and others

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.



Bob Bolles
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View excerpts from Serious Straw Bale at:
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