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Re: GSBN:More moisture problems - Southern California


It seems as the years go by, we are all becoming quasi moisture experts.
 As time goes by, we are going to see more of this, and it makes you
wonder how long all of us will be in business if it becomes too
widespread.  As Paul put it, it is part of straw bale growing up.

I have inspected two bale buildings built with parapets that incurred
moisture damage.  The first was a visitor center for the Nature
Conservancy near Colorado Springs about 7 years ago.  Water was making
it's way into the walls where the parapets and roof overhang met.  The
roof sloped to the north where the parapet was absent, and overhung the
wall by about 12".  The flashing and roofing at this juncture were very
poor and we could see down into the wall.  These two locations were at
the north corners of the building (east and west ends of the north
wall).  The water would travel straight down and hit rebar staples used
at the corners during construction.  This caused the water to spread out
and damage a larger area.

There were cracks in the plaster on the parapets and a small (relatively
speaking when compared to other areas) amount of moisture was making
it's way into the walls.  However, it did not appear to be the major
source of damage that occurred.

There were other areas of damage particularly under windows.  Caulk was
not present and the windows were not flashed properly.  There were no
windows sills.

Remediation of these problems included ripping off areas of plaster and
removing the slimy bales.  They were replaced with new bales or cob and
re-plastered.  The roof details were repaired and everything caulked.  I
did not do this work, but observed it's progress a couple times.  The
cost of doing this work was on the order of $40,000.

The second project was more recent in Salida, Colorado.  David Eisenberg
and Laura Struempler also visited this project.  They may have
additional insight in addition to my comments here.  The parapets were
made of bales and everything was encased in wet applied foam over and
down to the bottom of the parapets.  Cement plaster was applied over the
parapets and down the wall.  Sod staples were used to attach the lath to
the parapets, through the foam, creating thousands of pathways for
moisture to migrate.  This seemed like the primary source of moisture.
The moisture rotted the bales everywhere and was working on the top
bales in the wall, below the parapet.  There was a significant amount of
moisture from these holes.  The foam trapped the moisture effectively
creating a mold experiment.  This owner ripped off all of the exterior
plaster and the bales on the entire structure after consulting with us.
 He framed a wall on the exterior sill plate and foamed against the
interior plaster which remained intact.  He then re-plastered the
sheathed framed the walls, still with parapets, but flashed better than
before.  He now has a framed house with parapets that are flashed and

The lessons learned from both of these projects are not as clear as they
may seem, but there are some to be learned, I think.

In the case of the Nature Conservancy building, they bit the bullet and
tore out the portions we tested as damaged.  The source of moisture was
clear both before and after the plaster was removed.  It appeared our
probing with a moisture meter was accurate enough to isolate the damaged

In the case of the Salida project, the damage was everywhere above the
roof deck, but not so apparent below.  The owner ripped out everything
just to make sure he did not have a bale house to sell in the future.

In both cases, IMHO, the type of plaster did not contribute to the
damage.  Both were cement plaster, but had it been earth or lime, the
same damage would have occurred because of the parapet details.  Whether
the damage could have been detected earlier with other plaster materials
is another question.

What I do know is that both builders thought they new what they were
doing at the time.  They made mistakes and did not seek out real
solutions to moisture control in buildings during the design process.
Both wanted to fix the problem and were convinced that they needed to
use solutions that would permanently fix the problem, as witnessed with
other systems like a sheet barrier.  However, without our help, the
problems would have continued because the systems they would have chosen
to "remedy" the problem would have been mis-applied.  The main lesson is
in the details!

The thought process that happens by lay-people during these times can be
wrought with emotion or clouded by partial information.  The owner of
the Salida house was explaining the problems by describing them as micro
and macro-climate scenarios within his walls.  He is a scientist by
profession and wanted to explain it in a precise way.  The fact was that
it was pretty simple and the remedy was to keep the water out that was
making it's way into the walls via the parapets.  Pretty simple, but it
took weeks to convince him that even though his micro/macro climate
scenarios may be valid to some extent, the solution was simple and
straightforward.  I had him flash the parapets to bring any water that
makes it through the plaster on the parapets back out.  This meant a
flashing line visible around the entire house at the base of the parapets.

A final chapter (and an aside to your concerns) to this saga was during
the ripping out of bales.  They were using power tools (circular saws
with abrasive blades) to cut sections of the exterior plaster before
ripping it off.  One day, sparks ignited the exposed straw in a high
wind and the house caught on fire while they were at lunch.  The fire
department came out and doused a corner of the house.  Talk about an
ongoing trauma/nightmare scenario!  The lessons from this is be careful
when doing remediation work.

Finally, I know that this may not offer you any solid answers to your
problems, but may help with detection of the extent of damage and how to
deal with it.  Sheet barriers would not help with either of these
scenarios.  Proper details are the most important issues when dealing
with long-term solutions.

In my opinion, we need to be proactive in discouraging flat-roof/parapet
designs for straw bale construction.  Bale walls are more susceptible to
moisture because they soak it up.  I agree with Paul's observation that
point source damage will not soak the entire bale wall unless there is a
course for the water to take that will lead it to the center of the
bales.  Moisture travels straight down, unless directed horizontally by
other means, such as a rebar staple.

Good luck in your investigation.  It will not be pretty!

Jeff Ruppert, P.E.

Odisea LLC
Ecological Building, Engineering and Consulting

Front Range Office 		West Slope Office
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