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GSBN: Digest for 11/10/05

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-> Moisture Problem
     by Paul Lacinski paul@...
-> Re: GSBN:Moisture Problem
     by Rene Dalmeijer rene.dalmeijer@...
-> Dan Smith for membership
     by Bruce King ecobruce@...
-> Re: GSBN:Dan Smith for membership
     by Judyknox42@...
-> Dan Smith for membership
     by "Bob Bolles" Bob@...


Date: 10 Nov 2005 11:18:20 -0600
From: Paul Lacinski paul@...
Subject: Moisture Problem

Hello all,

Well, we have now had a significant failure.  The owner of one straw
bale house here (on which I served as a consultant and led the
plaster and bale work) has removed his straw bale walls after only 2
years, because of moisture problems.  I wasn't part of the
deconstruction (this is both merciful and unfortunate) but I have a
good idea of what was going on beforehand, and I've spoken to Jim
McSweeney, the owner, about what he found.  I'll attempt to convey it
here.  At the end of this email there will also be some questions- I
hope you all will have some ideas to share.

To begin at the beginning:

Last February, after a particularly cold spell, I noticed a pattern
of wetness at the outside top of the north wall, which appeared as if
water had been poured along the top edge of the wall, and allowed to
run down.   Jim removed the blocking at the end of the rafter bays,
and found ice on the underside of the sheathing, and also on the
underside of the proper vent that was installed at the upper part of
the rafter cavity, to maintain a ventilated air space.  The extreme
wetness on the surface of the plaster was caused by water (clearly
condensate- the standing seam roof could not be leaking in every bay)
running down the proper vent, hitting the blocking at the exterior of
the wall, and running down the back side of the blocking, into the
outer 2" of the bale, and into the plaster.  The outer 12-24 inches
of cellulose was also quite wet.

This house is of post and beam construction, with bales wrapped
around the structure, and dense-packed cellulose in cathedral
ceilings.  The walls had approximately 1" of lime stabilized clay
plaster, with a lime finish coat, and limewash.  Plaster and finishes
were the same inside and out, except for the bathroom, where a
conventional paint was applied to the interior, in place of the
limewash.  (I doubt that it was an especially vapor-retardant paint,
though I'm not sure.)  The ceiling is 1/2" drywall with latex paint,
poly, and dense-packed cellulose.  The cellulose ends atop the bale.
Interior butt joints between plaster and timber framing were backed
with 15 lb felt, in an attempt at tightening the joint against air

In late February, Jim took a set of moisture readings which showed
alarmingly high moisture levels in the outer 3-6" of the walls, often
in the range of 25-40%.  Unfortunately, I don't have any records of
these readings; they seem to have been only loosely correllated to
depth. I then took a set of readings (in different but nearby holes)
in mid-June.  By this time there had been considerable drying; while
there were many readings still in the high teens and 20's, there were
none in the 30's, and all high readings were in the very outer inch
or so of the straw, just behind the exterior plaster.  The inner
third of the bale was consistently at 8-12%, and the middle third at
8-15%.  Even the outer third of the wall, except for that last inch,
ranged from 10-20%.  Jim had found that the highest exterior numbers
were on the east wall, which is most exposed to rain, and receives
some spray from an adjoining roof.  This still seemed to be the case
in June.  I also pulled straw from the drill holes, and found some
minor discoloration, but no evidence of fiber breakdown.

In October, Jim tore down the walls.  The patterns he found speak
clearly of interior moisture sources, and also correlate to the
long-held idea that areas of lesser density are in greater danger of
moisture damage.  The places where the straw was in worst shape were
at joints between straw and wooden members, and also at the corners
of bales.  In some of these areas the fiber breakdown was such that
he could crumble the straw in his hand. Some of these areas would be
places where air leakage was a possiblility- around windows and
timbers, for instance.  (The wettest point was clearly one of these-
a large joint between bale and timber that was imperfectly sealed
with spray foam, because it was impossible to plaster this area.
Some plywood in the outer section of this wall was saturated and
delaminating, and carpenter ants had moved into the structural
timber, at the inside of the bale wall.)  But direct air leakage
could not have been possible for depositing moisture in all of the
problem places- many of the wood/straw joints and essentially all of
the bale/bale joints would be buried in the field of the wall, with a
continuous skin of plaster over each face.  This seems to corroborate
the theory that internal convection loops- or some pattern of air
motion- are causing water to be deposited in the outer section of
these less dense areas.  By contrast, the main body of each bale (or
at least the great majority of bales) was relatively intact, with
only a thin layer of damage at the very outer surface.  Additionally,
the wall which received more wetting from rain did not show a greater
degree of decomposition than the others.

For some time now, I have been musing on the possibility that the
plaster system that we use- equally permeable on the two sides of the
wall- may not be suitable for this climate.  I know of three of our
projects that show the annual damp patches in the upper areas of the
exterior walls.  I have been taking occasional moisture readings in
one (buried wood block sensors) and these seem to indicate a pattern
of increasing moisture levels through the wall section, from inside
to outside, during the cold season.  Of course, there are also many
houses that show no visual (or olfactory!) signs of moisture
accumulation.  Only one is anything like the extreme of Jim
McSweeney's house- but this was pretty clearly a different situation,
a hilltop site where a combination of a failed finish coat and severe
windblown rain caused water to enter the bales at the corners of the
building.  (Interestingly, in this house, it was only the areas of
30+% mc that showed any damaged straw; the 20+ areas felt damp to the
touch but were bright and intact.)

I think the McSweeneys' house showed such severe signs so quickly
because of two factors-

1- Higher than usual (for SB) moisture production within the house.
The McSweeneys had not been venting showers, were drying laundry in
the house(including diapers) with no ventilation, and had a pot of
water on the woodstove. The McSweeneys reasonably felt that their
practices were safe, because 3 humidity guages in the house were
reading consistently in the area of 40%.  But the extra moisture had
to be going somewhere.  It seems that it was exiting in large amounts
through air leakage at the tops of the walls, at the plaster/timber
intersection.  But the generally high moisture levels in the field of
the wall also indicate that it was working through the plaster by
diffusion, and that the resulting condensation at the back of the
plaster was not drying fast enough to prevent accumulation. The fact
that other houses are showing damp patches in late winter indicate
that this is not an isolated case, even if it is extreme.

2- Weather.  The summer in which this house was built (2003) was very
wet and not very hot.  The base coat of plaster took 2 weeks to
stiffen, and weeks passed before the surface appeared dry, on any
wall other than the south.  Finish coats were applied in late summer
(exterior, in the rain) and in early winter (interior.)  The owners
then left for much of the winter of 2003/2004, leaving the building
unheated.  During the summer of 2004, the red oxide colored exterior
limewash developed a splotchy character, with whitish surface
deposits.  In retrospect it seems reasonable to think that this was
caused by moisture migrating out through the walls.  For a long time
I have been saying that "plaster adds a totally unacceptable amount
of water to bale walls."  This is mostly a way of cautioning people
against applying the interior finish coat too quickly, before the
bales have a chance to dry off the water from the base coat.  In this
case, the walls may never have dried completely.

So now the big question- what to do?  Jim McSweeney is understandably
convinced that straw bale construction can't work in this climate.  I
tried on that idea, but it doesn't seem right.  What is clear is that
a system of equal permeablity rates on both sides of the wall is not
the best choice for colder and wetter climates.  It appears to be
working on lots of houses- and it's definitely working on at least
two that have sensors installed- but it is just as clearly not
working on the houses with damp patches.  (From Jim McSweeney's
experience  I feel it is safe to conclude that seasonal damp patches
are not OK- they are almost definitely causing some degree of
deterioration of the straw.)  The difference may have to do with
usage patterns.  But if straw bale houses are supposed to last
indefinitely (250+ years, by the standards around here) we cannot
reasonably expect every future family to be obsessive about a dry
indoor environment.

I hate to admit this, but I will- for some time now, I have been
thinking that with a clay/lime/ limewash or silicate paint exterior
system, it would be wise to use a commercial vapor-retardant paint on
the interior, to reduce the permeability of the interior wall
surface.  But the problem is that no painted bale wall ever has the
same timeless feeling as a limewashed bale wall- and this feeling is
a big piece of what make straw bale houses such wonderful spaces.  So
I've been resisting this idea.  But what other realistic options are
there?  We aren't going to come up with a way of dramatically
increasing the permeability of the exterior.  Increasing the
thickness of the interior plaster is a nice idea for a whole set of
reasons, but applying ~1.5"~ as we currenly do, is already a lot of
work.  Trying to double or triple that amount (Would this
dramatically change the permeability?  Anybody know?) seems wholly
impractical, for any building larger than a shed.

Interestingly, we usually do paint kitchens and bathrooms, because of
the unusually high moisture production in the these rooms, and also
for cleanability.  In the two houses where I have taken readings, I
have not found appreciably lower moisture readings in the walls
behind these painted bathroom surfaces.  I have assumed that this is
because the exterior bathroom walls are typically pretty small, and
so the moisture level will tend to equalize with that of adjacent
wall areas.  Also, I don't believe that either of these bathrooms is
painted with a particularly aggressive vapor retarder.  Any ideas,

I understand that there is also a danger in dramatically reducing the
permeability of the interior surface- in the case of major water
damage (roof leaks, etc) the ability to dry to the interior can be
very important to the health of the walls.  But we know, from good
quality conventional construction, that less permeable inside, more
permeable outside is what works for everyday conditions.  Why should
bales be any different?  And aren't everyday conditions ultimately
more of a driving concern than individual events?

Thanks for reading through this, and for any thoughts that you may
have.  I recall musing, at the time of Danny Buck's repair project,
that failures mean straw bale construction is finally coming of age.
Now I feel like I've aged a few years, as well- though not nearly so
many as Jim McSweeney, who is paying quite a lot to have his walls
rebuilt with studs and cellulose.

Thanks again for any thoughts you may provide.

All the best,


- --
Paul M. Lacinski
Sidehill Farm
GreenSpace Collaborative
Mail: PO Box 107
Packages: 137 Beldingville Rd.
Ashfield, MA 01330 USA
+1   413 628 3800

View excerpts from Serious Straw Bale at:
<a  target="_blank" href="http://www.chelseagreen.com/2004/items/seriousstrawbale";>http://www.chelseagreen.com/2004/items/seriousstrawbale</a>

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Date: 10 Nov 2005 14:46:28 -0600
From: Rene Dalmeijer rene.dalmeijer@...
Subject: Re: GSBN:Moisture Problem


Thanks very much for your frank and open report on the McSweeney house.
I see some parallels to house I have just help complete. Since
plastering the exterior with a hydraulic plaster I have monitored the
moisture level. Specifically because we noticed a damp spot on the
exterior on the spot most exposed to weather that only went away slowly
after removing the scaffolding. The spot dried in about 2 weeks it is
not visible anymore. After doing some hard thinking I realized it was
caused  by splash from water dripping from a roof drain on the scaffold
hitting the wall where the wet spot was only noticed after the scaffold
was removed.

Now back to the parallel with the McSweeney house. The wet spot
prompted me to regularly monitor the bales around the house. We only
just plastered a few of the interior walls with earth plaster so most
places were and are easily accessible from the inside. Instead of the
moisture levels dropping, what I expected, They have been rising not
much but up from 14% to 16% and only on the very outside 30-50mm. The
wet spot is slowly drying albeit very slowly. The house is not occupied
yet and is well ventilated.

Your mail has warned me though to keep a careful watch on the house. As
I subscribe to your idea that the Scandinavian model of having less
permeable finishes on the inside and more open finishes on the exterior
is good practice in the Dutch type of climate. I would love to do a
dynamic moisture transport simulation to better understand what is
happening. Sven Eweleit of Andersehen might be able to help.

On Nov 10, 2005, at 17:19, Paul Lacinski wrote:

> At the end of this email there will also be some questions- I
> hope you all will have some ideas to share.


Date: 10 Nov 2005 15:45:48 -0600
From: Bruce King ecobruce@...
Subject: Dan Smith for membership

Howdy --

I recently learned that Dan Smith, a Berkeley architect known to most
of you, is not on this list, and emphatically should be.  Dan has
designed and built more straw bales structures than any architect I
know of, anywhere, and has a keen eye for both the aesthetics and
technical aspects of SB construction.

I nominate him for membership, starting asap.  Seconds?

PS:  thank you, Paul Lacinski, for a very carefully written and
thorough report.  You ought to write a book!

Saludos a todos,

Bruce King, PE
Director, Ecological Building Network  ( www.ecobuildnetwork.org )
Publisher, Green Building Press  ( www.greenbuildingpress.com )
209 Caledonia St.
Sausalito, CA 94965  USA
(415) 331-7630
bruce@ ecobuildnetwork.org

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Date: 10 Nov 2005 16:29:49 -0600
From: Judyknox42@...
Subject: Re: GSBN:Dan Smith for membership

Matts and I second and second the nomination of Dan Smith.

Judy Knox and Matts Myhrman
Out On Bale
1037 E. Linden St.
Tucson, Az  85719

Each of us can and must champion the evolutionary breakthroughs necessary to
sustain all life.  The journey of a champion is difficult, AND our access to a
joyful life.
Judy Knox

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Date: 10 Nov 2005 16:38:02 -0600
From: "Bob Bolles" Bob@...
Subject: Dan Smith for membership

I would be proud to second that nomination.

I also thank you, Paul, for the candor and well thought out report.


Bob Bolles
Join our Community bulletin board

Bruce King wrote: > I recently learned that Dan Smith, a Berkeley architect
known to most
> of you, is not on this list, and emphatically should be.  Dan has
> designed and built more straw bales structures than any architect I
> know of, anywhere, and has a keen eye for both the aesthetics and
> technical aspects of SB construction.
> I nominate him for membership, starting asap.  Seconds?
> PS:  thank you, Paul Lacinski, for a very carefully written and
> thorough report.  You ought to write a book!
> Saludos a todos,
> Bruce King, PE


End of Digest

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