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GSBN: Digest for 11/15/05



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-> RE: GSBN:Moisture Problem
     by "Dan Smith" dan@...
-> Re:Moisture Problem:: dynamic moisture transport simulation
     by "Dirk Scharmer- FSB" ds@...
-> RE: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation
     by "John Straube" jfstraube@...
-> RE: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation
     by "Dirk Scharmer- FSB" ds@...
-> re: Moisture Problem
     by archilogic@...
-> Moisture Problem
     by "Habib John Gonzalez" habibg@...
-> Re: GSBN:Moisture Problem
     by Rene Dalmeijer rene.dalmeijer@...
-> re: Moisture Problem (Addendum(b))
     by archilogic@...
-> RE: GSBN:re: Moisture Problem
     by "John Straube" jfstraube@...
-> Re: GSBN: Moisture failure
     by Graeme North ecodesign@...


----------------------------------------------------------------------

Date: 14 Nov 2005 23:59:54 -0600
From: "Dan Smith" dan@...
Subject: RE: GSBN:Moisture Problem

Hello Paul, 

Iive been following this discussion with interest, empathy, and renewed
appreciation for our California climate.  As John says, top of the wall
detailing does seem key.  The amount of condensation you describe is
remarkable, and it makes me think there must be air leakage not just
vapor migration, and perhaps the vents in this case are more of a
condensation problem than cure.  

How are the inside joints between wall and ceiling sealed?  Is there an
air barrier and/or vapor barrier between the insulation and vent space?
Iim not sure what you mean by a iproperi vent, is that an impermeable
plastic tray.
As with the wall, in that climate I think youid want a less permeable
interior ceiling surface and more permeable membrane to the upper vented
space, if you have venting.  

We recently did a bale house in Wyoming, and the cathedral ceilings were
unvented with 1-2i of rigid foam sprayed under the roof sheathing, and
the balance filled with batt insulation (as dense spray cellulose was
unavailable).  Here in Calif. we typically now use dense pack cellulose
in unvented rafter bays.  

I know that venting is traditional, and should help, but Iive also heard
John Straube say the typical 1-2i of air space in a vented cathedral
ceiling is too minimal for good air movement.   

Thanks for describing the problems and conditions so thoroughly, it is
certainly perplexing, and my take on it is from a decidedly drier side
of the country.   

Dan Smith


- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of John
Swearingen
Sent: Monday, November 14, 2005 7:19 PM
To: 'GSBN'
Cc: arete33@...
Subject: RE: GSBN:Moisture Problem

Hi, PaulO

 

Of course few of the sites where we build can be called extreme
climates,
unless you call them extremely mild, so we havenit seen the occurrence
of
wet patches you describe, but they do make sense. Iive been impressed by
the
degree to which vapor migrates around inside the bale walls, and how
warm
vapor rises.  If it encounters a cold surface, then naturally it will
condense.

 

Vents would be one solution, though as you suggest they might be the
cause
of other problems.  Another alternative is solid insulation at the top
of
the bales.  We are fans of box beams (though they seem to be going out
of
style), and one of the many good things about them is that they provide
a
highly insulated and vapor impermeable layer on top of the bale walls,
similar in effect to a top plate in stud construction.  It would be
unusual
for the underside of a plywood box beam to ever get so cold as to
trigger
condensation.

 

In any event, I think weire reaching some sort of conclusion, that the
solution to the roof condensation condition lies in detailing the top of
the
wall...

 

John

 

 

 

John Swearingen

Skillful Means

design and construction

www.skillful-means.com

 

 

- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Paul
Lacinski
Sent: Monday, November 14, 2005 4:08 PM
To: GSBN
Cc: arete33@...
Subject: RE: GSBN:Moisture Problem

 

Hi John,

 

Thanks for your thoughts.  What you are saying about the stored water

from construction as the primary source may well be correct.    As I

mentioned, I'm of the firm opinion that plastering adds too much

moisture to the walls.  But what are we to do about it?  Not much

that I've thought of, other than providing excellent ventilation (and

heat if necessary) and hoping for good drying weather.  Also-

avoiding the application of interior finish coats until the bales

(checked with a moisture meter!) have dried out from the deluge of

the base coat.

 

I would certainly agree that any vapor retardant layer on the

interior shouldn't be applied until the bales have dried fully.  Once

again, this would require testing- something that we (and, I suspect,

95% of bale builders) have been less than rigorous about.

 

Still, I see this house an extreme example of what seems to be a

common pattern- the appearance of the damp patches.  The houses that

get them just seem to get them every year, both during and after the

initial drying-out period.  I don't yet have enough experience to

correlate them to a source- is there a pattern of occupant behavior?

Or some particular construction detail?  I don't yet know how common

they are, though I'm sure that the majority of houses don't get them;

otherwise I would have heard from alot more than 3 people, by now.  I

do know that they always appear at the upper part of the wall, and

are most common right at the top of the bale wall, where the bale

meets the roof insulation.  They also appear in the same locations

every year.

 

Though I think you understand, I'd like to clarify a bit on the water

from the roof.  From a design point of view, it's nothing to do with

an external source.  Whether the moisture was from construction or

from internal production, it clearly made its way out the top of the

bale, where it then condensed on the roof, and ran back down as

liquid.  Early on I was hoping that the source might be the roof

ventilation air- we have an issue here with condensation from the

ventilation air on the underside of metal roofs.  But this is not a

February phenomenon; it happens in spring in fall when days are warm

and relatively humid, and nights are cold.  It's like dew, but upside

down; and it happens quickly because the metal roofs cool so quickly.

You can get ice at night, and rain inside the under-construction

building in the morning.  The first time I experienced this, I was

asleep on a stack of that first-generation cotton insulation that

didn't loft enough to insulate well, but made a nice site mattress.

The sun was up before me, and as soon as it hit the roof I got pretty

wet.  It's always nice to have a freakout in the morning, before even

brushing your teeth.

 

I remember hearing Tim Owen-Kennedy talking about venting the upper

part of bale walls to the outside, to prevent moisture accumulation

in the roof.  At the time, I wasn't sure it made sense; it seemed to

me that by leaving openings in the exterior plaster, you would be

increasing the rate of air leakage from the interior of the building

through the wall, and thus potentially increasing the rate of

deposition.  But I think I might be convinced.

 

So what if these questions were to be separated?  First, we have a

rather obvious (in retrospect) need to make sure the walls can dry

off construction moisture, as soon as possible.  But once that has

happened, in a cold climate, should we be seriously (I still don't

like that word) considering a vapor retarder on the inside, maybe in

conjunction with Tim's vents?

 

Thanks again,

 

Paul

 

 

 

 

 

>Paul,

>Iim a bit confused by an assessment of the sources of the moisture.  In

>the first part of your description, you describe an external source of,

>apparently, a good deal of water, coming from condensation around the

>top of the roof.

>

>iThe 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 2i of the bale, and into the plaster.i

>

>But then, after tearing open the walls, you remarked that:

>

>iThe 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.i

>

>Itis clear that the bales were subjected to lots of moisture.  First,

>during the wet summer of plastering, when apparently drying of the

>considerable moisture introduced through plastering was very slow; then

>during the following winter, when the house was unheated, and therefore

>unable to dry out; and finally because of the roof vent condition.

>

>So I wonder whether what you are taking to be evidence of iinterior

>moisture sourcesi isnit just an observation of the pattern of moisture

>migration (and collection) as the moisture laden walls (attempted to)

>dry out.

>The relatively humid interior conditions, in this case, wouldnit be the

>cause of the excessive moisture, but would have resulted in a sluggish

>drying process which, given the amount of water the bales had stored

>during construction and the winter, and the input of water from the

>roof, was insufficient to dry the bales before damage occurred.

>When bales are moisture laden, the moisture will transport and migrate

>all around the walls, in and out, up and down, depending on eclimatei,

>even on a daily basis.  So perhaps you are seeing evidence of the

>dominant pattern of moisture migration in the walls, but not of the

>introduction of moisture from the interior.

>This would indicate that the lack of barrier on the interior is
actually

>working to dry the wall: The gradation of humidity from dry at the

>interior to moist at the outside may be evidence that the

>humidity/temperature/pressure differential between inside and out is

>actually working to drive moisture out of the walls, but was

>insufficient to do the job before damage occurred.

>But then again, I havenit seen the wallsO.what do you think?

>

>John

>

>John Swearingen

>Skillful Means

>

>

>

>-----Original Message-----

>From: GSBN HYPERLINK

>"<a  target="_blank" href="mailto:%5bmailto:GSBN@...%5d"[mailto:GSBN@lists.gre";>mailto:%5bmailto:GSBN@...%5d"[mailto:GSBN@...
e

>nbuilder.com] On Behalf Of Paul Lacinski

>Sent: Thursday, November 10, 2005 8:19 AM

>To: HYPERLINK

>"<a  target="_blank" href="mailto:GSBN@..."GSBN@...";>mailto:GSBN@..."GSBN@...

>Subject: GSBN: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 wasnit part of the deconstruction
(this

>is both merciful and unfortunate) but I have a good idea of what was

>going on beforehand, and Iive spoken to Jim McSweeney, the owner, about

>what he found.  Iill 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 2i 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 1i 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 Iim not sure.)  The ceiling is

>*i 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 leakage.

>In late February, Jim took a set of moisture readings which showed

>alarmingly high moisture levels in the outer 3-6i of the walls, often
in

>the range of 25-40%.  Unfortunately, I donit 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 20is, there were none in the 30is,

>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 McSweeneyis 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 McSweeneysi 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 iplaster

>adds a totally unacceptable amount of water to bale walls.i  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 canit work in this climate.  I

>tried on that idea, but it doesnit 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 itis 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 McSweeneyis 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 Iive been

>resisting this idea.  But what other realistic options are there?  We

>arenit 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 ~1.5i~

>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

>donit believe that either of these bathrooms is painted with a

>particularly aggressive vapor retarder.  Any ideas, here?

>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 arenit 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 Buckis repair project, that

>failures mean straw bale construction is finally coming of age.  Now I

>feel like Iive 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

>

>

>--

>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:

>HYPERLINK

>"<a  target="_blank" href="http://www.chelseagreen.com/2004/items/seriousstrawbale"http://www.che";>http://www.chelseagreen.com/2004/items/seriousstrawbale"http://www.che</a>
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- --

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:

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----------------------------------------------------------------------

Date: 15 Nov 2005 10:26:38 -0600
From: "Dirk Scharmer- FSB" ds@...
Subject: Re:Moisture Problem:: dynamic moisture transport simulation

Rene,
I'll try to contribute a little to the moisture discussion by giving a short
summary to our acitivities in this field. Sorry for not corresponding
directly to the earlier messages.

In the last months we did some straw bale- 'dynamic moisture transport
simulation' with WUFI. You'll find some english description about WUFI at
<a  target="_blank" href="http://www.wufi.de/index_e.html";>http://www.wufi.de/index_e.html</a>. But I guess you know this software. It
seems to be one of the worldwide standards systems for this task.

The 'Fraunhofer Institut Bauphysik' did the straw bale simulations. They
also did a lot of publications to hygrothermal behaviour of walls. You'll
find them on their (english) website:
<a  target="_blank" href="http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html";>http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html</a>. Take a
closer look to the dissertation of Sedlbaur.

The report about two strawbale walls we assigned gives the following
results:

1. In german standard climate (Holzkirchen) unprotected straw bales (but
under roof) molds(!).
This is merry nonsense, but it shows, that this dynamic simulation software
calculates to surely for our straw bales.
2. As expected after the first point above, our straw bale wall with 3cm
wheat stabilized clayplaster, 45cm straw, 3cm interiour clay plaster, molds
at about 6000 hours in the year. In reality the wheat stabilized clayplaster
works wunderful, for example at www.fasba.de >> projekte  >> Strohpolis.
3. An alternative wall construction, which we don't prefer,
behind-ventilated timber cladding, 2cm wood soft fiber, 35cm straw, 1,5cm
OSB interiour doesn't mold.

Now we've at least one configuration which works under dynamic simulation
done by computer. The reality is fortunately more friendly to our bales. In
the next months, we've to find a way to proove the clayplaster option.

To the moisture problem of Paul Lacinski's client:
I had a moisture problem with a lime layered clayplaster in this summer too.
We had to renew the weathersided (western) wall of the straw bale house.
You'll find it on www.fasba.de >> projekte  >> Schier.

We assume, that the 'resistance against vapor' (accurate expression?) of the
lime layer was too high, but let too much driving rain coming in.
I had not enough endurance to read all the partly very long messages from
the moisture thread, but I guess the problem Paul Lacinski's client had is
not similar to our's above.

We took at a time 10 straw samples from 5 buildings and analyzed their
content of fungus. Two samples showed (amongst others the weatherside of
House Schier) much above common house dust concentration of fungus.

Puh, several month since I had to write english...

(On Thursday the german licensing authority decides about our request for a
general german approval of straw bales as infill insulation, our main
challenge was to prove, that straw bales don't mold)


Dirk Scharmer
www.fasba.de

- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Rene Dalmeijer
Sent: Thursday, November 10, 2005 9:43 PM
To: GSBN
Subject: Re: GSBN:Moisture Problem

Paul,

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.


Rene
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.

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.
- ----



----------------------------------------------------------------------

Date: 15 Nov 2005 10:53:56 -0600
From: "John Straube" jfstraube@...
Subject: RE: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation

Hi all!
Great to see Dirk doing analysis and moving this forward. I am not sure what
you mean by WUFI "predicts mold" though, and this could be important.

I have run thousands of different WUFI simulations  on hundreds of different
walls, including strawbale walls, which we correlated to field performance
at the Ridge winery building. It is quite accurate for predicting the
temperature and moisture conditions for strawbale walls if you get the input
data correct, however, IT DOES NOT PREDICT MOLD GROWTH.  I emphasize this
because WUFI is widely used and people often apply WUFI-Bio (a separate
program) or simple 80%RH thresholds to assessing mold growth. We have never
been able to get correlation from field or lab measurements of wood and
paper RH and temperature and mold growth.  Almost all rules are VERY
conservative

The interpretation of mold growth thresholds is, I believe, what explains
Dirk's successful field results .


Dr John Straube
Associate Professor
Dept of Civil Engineering &amp; School of Architecture
University of Waterloo
Waterloo, Ont. Canada
<a  target="_blank" href="http://www.civil.uwaterloo.ca/beg";>http://www.civil.uwaterloo.ca/beg</a>


- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Dirk Scharmer-
FSB
Sent: Tuesday, November 15, 2005 11:22 AM
To: 'GSBN'
Subject: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation

Rene,
I'll try to contribute a little to the moisture discussion by giving a short
summary to our acitivities in this field. Sorry for not corresponding
directly to the earlier messages.

In the last months we did some straw bale- 'dynamic moisture transport
simulation' with WUFI. You'll find some english description about WUFI at
<a  target="_blank" href="http://www.wufi.de/index_e.html";>http://www.wufi.de/index_e.html</a>. But I guess you know this software. It
seems to be one of the worldwide standards systems for this task.

The 'Fraunhofer Institut Bauphysik' did the straw bale simulations. They
also did a lot of publications to hygrothermal behaviour of walls. You'll
find them on their (english) website:
<a  target="_blank" href="http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html";>http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html</a>. Take a
closer look to the dissertation of Sedlbaur.

The report about two strawbale walls we assigned gives the following
results:

1. In german standard climate (Holzkirchen) unprotected straw bales (but
under roof) molds(!).
This is merry nonsense, but it shows, that this dynamic simulation software
calculates to surely for our straw bales.
2. As expected after the first point above, our straw bale wall with 3cm
wheat stabilized clayplaster, 45cm straw, 3cm interiour clay plaster, molds
at about 6000 hours in the year. In reality the wheat stabilized clayplaster
works wunderful, for example at www.fasba.de >> projekte  >> Strohpolis.
3. An alternative wall construction, which we don't prefer,
behind-ventilated timber cladding, 2cm wood soft fiber, 35cm straw, 1,5cm
OSB interiour doesn't mold.

Now we've at least one configuration which works under dynamic simulation
done by computer. The reality is fortunately more friendly to our bales. In
the next months, we've to find a way to proove the clayplaster option.

To the moisture problem of Paul Lacinski's client:
I had a moisture problem with a lime layered clayplaster in this summer too.
We had to renew the weathersided (western) wall of the straw bale house.
You'll find it on www.fasba.de >> projekte  >> Schier.

We assume, that the 'resistance against vapor' (accurate expression?) of the
lime layer was too high, but let too much driving rain coming in.
I had not enough endurance to read all the partly very long messages from
the moisture thread, but I guess the problem Paul Lacinski's client had is
not similar to our's above.

We took at a time 10 straw samples from 5 buildings and analyzed their
content of fungus. Two samples showed (amongst others the weatherside of
House Schier) much above common house dust concentration of fungus.

Puh, several month since I had to write english...

(On Thursday the german licensing authority decides about our request for a
general german approval of straw bales as infill insulation, our main
challenge was to prove, that straw bales don't mold)


Dirk Scharmer
www.fasba.de

- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Rene Dalmeijer
Sent: Thursday, November 10, 2005 9:43 PM
To: GSBN
Subject: Re: GSBN:Moisture Problem

Paul,

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.


Rene
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.

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.
- ----

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.
- ----



----------------------------------------------------------------------

Date: 15 Nov 2005 11:39:48 -0600
From: "Dirk Scharmer- FSB" ds@...
Subject: RE: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation

Dear John,
The WUFI- Experts (Dr.Martin Krus) of the Fraunhofer Institute indeed took
WUFI-Bio for predicting mold growth.
Therefore they classified straw in substrate class 1 (mold growth
threshold). The substrat class 1 gives an isopleth of humidity an
temperature for mold sprout and growth. For pure laboratory research this
isopleth and WUFI-Bio seems to be well validated. Also they tested (very
expensive!) our clayplaster to get the correct input data for WUFI.

I discussed the findings with Sedlbaur and Krus, but their believe in WUFI
seems to be unlimited.

What is our back door? To find out a special straw isopleth?

What results did you get with comparable strawbale wall (3cm clay, 35cm
straw, 3cm clay)?

By the way: The german licensing authority demands the mold-free evidence
with WUFI? The bad alternative is the normal german mold test (DIN IEC 68 2
10) with nearly 100%RH and 30#161#C over 28 days by infecting the straw with a
dozen mold spores. Under this conditions straw will molder after 2 days and
will fail the approval.

The goal of WUFI is to say: Is the straw bale construction SURELY staying
for years free of molder? This is the sticking point we have to come over. 
How do you solve this?

How do you judge the mathematical model of WUFI-Bio? Isn't the way to
calculate a single spore a little bit absurd?

Dirk (really excited to have found a Straw-WUFI-Expert out there)



- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of John Straube
Sent: Tuesday, November 15, 2005 5:48 PM
To: 'GSBN'
Subject: RE: GSBN:Re:Moisture Problem:: dynamic moisture transport
simulation

Hi all!
Great to see Dirk doing analysis and moving this forward. I am not sure what
you mean by WUFI "predicts mold" though, and this could be important.

I have run thousands of different WUFI simulations  on hundreds of different
walls, including strawbale walls, which we correlated to field performance
at the Ridge winery building. It is quite accurate for predicting the
temperature and moisture conditions for strawbale walls if you get the input
data correct, however, IT DOES NOT PREDICT MOLD GROWTH.  I emphasize this
because WUFI is widely used and people often apply WUFI-Bio (a separate
program) or simple 80%RH thresholds to assessing mold growth. We have never
been able to get correlation from field or lab measurements of wood and
paper RH and temperature and mold growth.  Almost all rules are VERY
conservative

The interpretation of mold growth thresholds is, I believe, what explains
Dirk's successful field results .


Dr John Straube
Associate Professor
Dept of Civil Engineering &amp; School of Architecture
University of Waterloo
Waterloo, Ont. Canada
<a  target="_blank" href="http://www.civil.uwaterloo.ca/beg";>http://www.civil.uwaterloo.ca/beg</a>


- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Dirk Scharmer-
FSB
Sent: Tuesday, November 15, 2005 11:22 AM
To: 'GSBN'
Subject: GSBN:Re:Moisture Problem:: dynamic moisture transport simulation

Rene,
I'll try to contribute a little to the moisture discussion by giving a short
summary to our acitivities in this field. Sorry for not corresponding
directly to the earlier messages.

In the last months we did some straw bale- 'dynamic moisture transport
simulation' with WUFI. You'll find some english description about WUFI at
<a  target="_blank" href="http://www.wufi.de/index_e.html";>http://www.wufi.de/index_e.html</a>. But I guess you know this software. It
seems to be one of the worldwide standards systems for this task.

The 'Fraunhofer Institut Bauphysik' did the straw bale simulations. They
also did a lot of publications to hygrothermal behaviour of walls. You'll
find them on their (english) website:
<a  target="_blank" href="http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html";>http://www.hoki.ibp.fhg.de/ibp/publikationen/publikationen_e.html</a>. Take a
closer look to the dissertation of Sedlbaur.

The report about two strawbale walls we assigned gives the following
results:

1. In german standard climate (Holzkirchen) unprotected straw bales (but
under roof) molds(!).
This is merry nonsense, but it shows, that this dynamic simulation software
calculates to surely for our straw bales.
2. As expected after the first point above, our straw bale wall with 3cm
wheat stabilized clayplaster, 45cm straw, 3cm interiour clay plaster, molds
at about 6000 hours in the year. In reality the wheat stabilized clayplaster
works wunderful, for example at www.fasba.de >> projekte  >> Strohpolis.
3. An alternative wall construction, which we don't prefer,
behind-ventilated timber cladding, 2cm wood soft fiber, 35cm straw, 1,5cm
OSB interiour doesn't mold.

Now we've at least one configuration which works under dynamic simulation
done by computer. The reality is fortunately more friendly to our bales. In
the next months, we've to find a way to proove the clayplaster option.

To the moisture problem of Paul Lacinski's client:
I had a moisture problem with a lime layered clayplaster in this summer too.
We had to renew the weathersided (western) wall of the straw bale house.
You'll find it on www.fasba.de >> projekte  >> Schier.

We assume, that the 'resistance against vapor' (accurate expression?) of the
lime layer was too high, but let too much driving rain coming in.
I had not enough endurance to read all the partly very long messages from
the moisture thread, but I guess the problem Paul Lacinski's client had is
not similar to our's above.

We took at a time 10 straw samples from 5 buildings and analyzed their
content of fungus. Two samples showed (amongst others the weatherside of
House Schier) much above common house dust concentration of fungus.

Puh, several month since I had to write english...

(On Thursday the german licensing authority decides about our request for a
general german approval of straw bales as infill insulation, our main
challenge was to prove, that straw bales don't mold)


Dirk Scharmer
www.fasba.de

- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Rene Dalmeijer
Sent: Thursday, November 10, 2005 9:43 PM
To: GSBN
Subject: Re: GSBN:Moisture Problem

Paul,

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.


Rene
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.

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.
- ----

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.
- ----

- ----
GSBN is an invitation-only forum of key individuals and representatives of
regional straw construction organizations. The costs of operating this list
are underwritten by The Last Straw Journal in exchange for use of the GSBN
as an advisory board and technical editing arm.

For instructions on joining, leaving, or otherwise using the GSBN list, send
email to GSBN@...HELP in the SUBJECT line.  
- ----



----------------------------------------------------------------------

Date: 15 Nov 2005 13:08:09 -0600
From: archilogic@...
Subject: re: Moisture Problem

On Fri, 11 Nov 2005
Paul Lacinski paul@... wrote:

> 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.

> found ice on the underside of the sheathing,

> outer 2" of the bale, and into the plaster.  The outer 12-24 inches
> of cellulose was also quite wet

> dense-packed cellulose in cathedral ceilings.

> The walls had approximately 1" of lime stabilized clay plaster, with a
> lime finish coat, >and limewash.

> The ceiling is 1/2" drywall with latex paint, poly, and dense-packed
> cellulose.


> 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%.


> in mid-June. 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%.

> highest exterior numbers were on the east wall, which is most exposed to
> rain, and >receives some spray from an adjoining roof.


  >But direct air leakage could not have been possible for depositing
moisture
> in all of the problem places

> 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.

> generally high moisture levels in the field of
> the wall also indicate that it was working through the plaster by
> diffusion,

Paul and GSBN Amiguettes and Amigos;

I haven't had a close look at the long,long long (and very nice, thank you
very much) report yet but my first response is  that I doubt very much if
vapour diffusion through the wall plaster is responsible for the wet walls
or that it's even an issue.

It never has been with conventional construction systems in Cold climates
and I think that it is even less likely with the thick wall plasters that
are typically used with SBC.
Besides, the greatest vapour pressure will be at the ceiling and its
vapour permeance (1/2" drywall) is higher than that of the wall plaster.

I suspect that the biggest culprits are rain wetting and air leakage.

The ice formation on the underside of the roof and the wet ceiling
insulation and top of the walls are strikingly similar to a classic
example of poor air sealing in the ceiling and poor attic ventilation.
Cathedral ceilings are particularly prone to the above symptoms because
they simply do not provide the attic volume that triangular trussed roof
systems provide.   The additional volume somewhat helps to alleviate the
poor ventilation condition somewhat by dispersing the trapped moisture but
of course, exhausting it altogether is preferable.

That the attic moisture then ran down to the bottom of the underside of
the roof and then rained onto the walls is not at all surprising.

While it is mentioned that there was a poly sheet used in ceiling beneath
the drywall and that there was tarpaper placed beneath the wall-ceiling
junctions, I am more than a little suspicious that
    (1) the poly was punched full of holes when installing the drywall
    (2) there are pentrations for electrical boxes and wiring that weren't
sealed
    (3) the joints between sheets of poly weren't made air-tight
... or in short, the air barrier is not.

As for the 40% interior relative humidity in winter, that's not
excessively high IMO.
I like to maintain at least that level in order to avoid the health
problems that are associated with the too dry winter conditions that are
typical of air-leaky buildings.

=== * ===
Rob Tom
Kanata, Ontario, Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff  from my edress in your reply)



----------------------------------------------------------------------

Date: 15 Nov 2005 13:37:39 -0600
From: "Habib John Gonzalez" habibg@...
Subject: Moisture Problem

Greetings:


Early in our bale wall moisture monitoring I noticed the initial high moisture
spike in the standard  five moisture sensors immediately after the stucco was
applied. The building grade bales generally arrived on site with a moisture
content between 9% to 12%. A few days after plastering the moisture content at
the sensors would be around 18% then begin to decrease steadily. Nearly all
these homes were finished immediately after the stucco work and the families
moved in. 

Sensor readings after the initial Canada Mortgage and Housing Corporation
study were then randomly taken as requested by the owners. This summer I
tested one home prior to its sale. The house has been occupied since completed
in 1997, the five moisture readings were between 7% to 9%. The house is
featured on pages 166-171 of Catherine Wanek's "The New Straw Bale Home."  It
sold for $450,000CND.

Two years ago master plasterer Gordon Askey elbowed his way into our stucco
work. His 35 years experience as a stucco contractor and innovator has proved
invaluable to our clients. He has concerns about late season plaster work in
unheated buildings due to the moisture load he feels the plaster puts on the
building. I mentioned this discussion to him this morning and he was very
clear about the need to gently heat the buildings in the fall and early
winter, particularly when the night time temperatures drop to minus 5 degrees
Celsius. Below 5 degrees he does not work outside. In the fall, if there is
any delay in installing the heating system in the newly plastered bale home,
he uses portable electric heaters and two dehumidifiers per house to protect
the bales. He did this for his first two bale home projects and was astonished
at the amount of water collected daily from the dehumidifiers. Gordon observes
the steady drying of the exterior plaster, even in cool conditions, he worries
about moisture trapped within the building.

The standard stucco product in this region by Lafarge; it has a composition of
70% Portland cement and 30% lime. It dries significantly over night and often
the walls need dampening before the second coat is applied. To avoid cracking
of the second coat by the suction of the first due to the drier initial layer,
Gordon "double backs" the plaster, a technique he learned as an apprentice. We
divide the job into workable segments with expansion joints on the outside
walls and use the interior posts as dividers. We spray this section with the
carrousel pump, level and edge it with trowels, scratch it with a broom, then
stop for lunch. We respray the same wall section again in the afternoon, often
with integral colour and float finish it. This system has drastically reduced
the cracking in the surface layer. 

Rain splashback off scaffolds has been a problem which we now avoid since we
hang tarps from the eaves of the building to prevent extreme weather, either
rain or  direct sun from damaging the new plaster. Our experience with
conventional stucco is it often dries quickly and has to be moistened between
coats. This is not the case with earthen plasters, which often take weeks to
dry between coats, allowing the bales to absorb increased amounts of moisture.

Yesterday an architect friend called from Washington state and I mentioned
this discussion to her. She too has concerns about clients who do not heat
their homes after the plaster is applied in the fall. She has seen earthen
plasters mould over winter due to this excessive moisture. 

Good ventilation, dry materials, safe placement of the building on the land,
best construction practices, special considerations to the conditions we
create with late season plastering, all important aspects of this work. 


My thanks to you all.


Habib

**********************************************************************************
Sustainable Works
Habib John Gonzalez
RR#1, S-4, C-12
Crescent Valley, British Columbia
Canada, V0G-1H0
tel/fax 250-359-5095
www.sustainableworks.ca
**********************************************************************************
"Better the kindness of imperfection than perfection without kindness"



- --- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
- ---


----------------------------------------------------------------------

Date: 15 Nov 2005 13:58:28 -0600
From: Rene Dalmeijer rene.dalmeijer@...
Subject: Re: GSBN:Moisture Problem

Paul and all the others,


Rene
On Nov 15, 2005, at 01:30, Paul Lacinski wrote:

Last weekend just before the first Dutch SB house tour started at the
IJburg house I managed to do some measurements again. The moisture
levels, besides the wet spot, are down again to normal ie 14-16%.

The wet spot due to the scaffolding splash zone is drying out albeit
very slowly.

> We have also had the splash problem from the scaffolding- it's very
> easy at the end of a long day to convince yourself that the planks
> are just fine where they are, even if they are under the drip line of
> the roof.   I'm not so surprised to hear that the moisture level is
> rising in that outer zone of your walls; if the plaster is still wet,
> the straw may still be absorbing moisture from it.

> My limited
> experience has been that that outer 30-50mm dries very slowly, and
> always experiences the most active cycling, from rain or from
> condensation.
>
> On two projects we tried Tom Rijven's dip method, but it was so messy
> and labor-intensive, and made the bales so heavy and the floor so
> slippery, that we quit.  But I wonder whether it isn't worth dipping
> the exterior face of the bales, because if that outer 30-50mm were
> impregnated with clay, I suspect that it would be alot more durable.

I have not built a real big house using this method but did a test wall
during a show and a very small outhouse using the dip method. The dip
layer dried quite rapidly about 1 hour after dipping. We completely
finished the plaster in about 3 hours after stacking the wall (for the
show wall and the smaal out house roughly the same). During both
occasions it was very nice weather although again on both accasoins we
also did have a short shower. I am really a big fan of the method it is
dirty but works very well for the reasons Paul mentions. I would like
to add dipping also removes the need for trimming.
>
> I'd love to see a simulation- if you decide to look into it let me
> know if I can pass on any information.  In your project, is the earth
> the finish material on the interior?  And if so, doesn't that create
> the opposite permeability ratios from what we have been discussing?

Yes earth is the interior plaster and yes it is opposite to what I
would like. A less permeable interior plaster with a more permeable
exterior plaster.

I fully support Dirks request for a more accurate prediction of
damaging moisture levels in organic materials. Is this possibly a Phd
research project? That would be great taking away a serious constraint
to the acceptence of (specifically in Germany) renewable regrowable
building materials. We all know they perform better then the numbers
tell. I wonder how wood fares within these simulations?

Thank you all for the replies.



----------------------------------------------------------------------

Date: 15 Nov 2005 14:10:31 -0600
From: archilogic@...
Subject: re: Moisture Problem (Addendum(b))

Scooz 'eh  Moi;

In his previous message, that dodo Stronzo di Nord forgot to ask:

"Were the rafters  (a) solid lumber (or TJIs)
                              or
                     (b) Scissors or parallel chord trusses ?"

                and

"What sort of a ventilation space was provided over the insulation in the
rafter bays of the cathedral ceiling  and what arrangement was used to
provide exhaust capability for the ventilation space ?"

=== * ===
Rob Tom
Kanata, Ontario, Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff  from my edress in your reply)



----------------------------------------------------------------------

Date: 15 Nov 2005 16:14:30 -0600
From: "John Straube" jfstraube@...
Subject: RE: GSBN:re: Moisture Problem

Rob Tom's analysis seems spot on.  Diffusion can be ruled out except in
cases with essentially no plaster on the interior and thick and/or
impermeable plaster on the exterior.
Air leaks are very very likely

I would not run 40%RH in outdoor temperatures much below 30 F, and most
windows (not good ones) will have condensation below this temperature at 40%
anyway.


Dr John Straube
Associate Professor
Dept of Civil Engineering &amp; School of Architecture
University of Waterloo
Waterloo, Ont. Canada
<a  target="_blank" href="http://www.civil.uwaterloo.ca/beg";>http://www.civil.uwaterloo.ca/beg</a>


- -----Original Message-----
From: GSBN [<a  target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Rob Tom
Sent: Tuesday, November 15, 2005 2:04 PM
To: GSBN
Subject: GSBN:re: Moisture Problem

On Fri, 11 Nov 2005
Paul Lacinski paul@... wrote:

> 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.

> found ice on the underside of the sheathing,

> outer 2" of the bale, and into the plaster.  The outer 12-24 inches of
> cellulose was also quite wet

> dense-packed cellulose in cathedral ceilings.

> The walls had approximately 1" of lime stabilized clay plaster, with a
> lime finish coat, >and limewash.

> The ceiling is 1/2" drywall with latex paint, poly, and dense-packed
> cellulose.


> 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%.


> in mid-June. 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%.

> highest exterior numbers were on the east wall, which is most exposed
> to rain, and >receives some spray from an adjoining roof.


  >But direct air leakage could not have been possible for depositing
moisture
> in all of the problem places

> 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.

> generally high moisture levels in the field of the wall also indicate
> that it was working through the plaster by diffusion,

Paul and GSBN Amiguettes and Amigos;

I haven't had a close look at the long,long long (and very nice, thank you
very much) report yet but my first response is  that I doubt very much if
vapour diffusion through the wall plaster is responsible for the wet walls
or that it's even an issue.

It never has been with conventional construction systems in Cold climates
and I think that it is even less likely with the thick wall plasters that
are typically used with SBC.
Besides, the greatest vapour pressure will be at the ceiling and its vapour
permeance (1/2" drywall) is higher than that of the wall plaster.

I suspect that the biggest culprits are rain wetting and air leakage.

The ice formation on the underside of the roof and the wet ceiling
insulation and top of the walls are strikingly similar to a classic example
of poor air sealing in the ceiling and poor attic ventilation.
Cathedral ceilings are particularly prone to the above symptoms because they
simply do not provide the attic volume that triangular trussed roof
systems provide.   The additional volume somewhat helps to alleviate the
poor ventilation condition somewhat by dispersing the trapped moisture but
of course, exhausting it altogether is preferable.

That the attic moisture then ran down to the bottom of the underside of the
roof and then rained onto the walls is not at all surprising.

While it is mentioned that there was a poly sheet used in ceiling beneath
the drywall and that there was tarpaper placed beneath the wall-ceiling
junctions, I am more than a little suspicious that
    (1) the poly was punched full of holes when installing the drywall
    (2) there are pentrations for electrical boxes and wiring that weren't
sealed
    (3) the joints between sheets of poly weren't made air-tight ... or in
short, the air barrier is not.

As for the 40% interior relative humidity in winter, that's not excessively
high IMO.
I like to maintain at least that level in order to avoid the health problems
that are associated with the too dry winter conditions that are typical of
air-leaky buildings.

=== * ===
Rob Tom
Kanata, Ontario, Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff  from my edress in your reply)

- ----
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----------------------------------------------------------------------

Date: 15 Nov 2005 19:05:54 -0600
From: Graeme North ecodesign@...
Subject: Re: GSBN: Moisture failure

Two things appear apparent to me.

The first is really obvious:

> 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.

What do you expect?  Any house of ANY type would show trouble with these
ownership practices.

I'm not sure what the roofing material is, or what the eaves overhangs are
in relation to the rainfall/driving rain index in this climate.  I assume
that there are generous eaves, and that the roof goes over the tops of all
the walls?  Any significant external wetting of the walls can not possibly
help
.
However, the other source of real trouble seems to be condensation in the
roof spaces running down the underside of the roofing material that has not
been directed to the outside well clear of the tops of the walls.

In temperate New Zealand at least we would put vapour barriers on the warm
(interior)  side of skillion (cathedral) construction in the ceilings of wet
rooms - eg bathrooms and laundry, possibly kitchen.
Underneath roof cladding we install breathable absorbent kraft paper
building wrap that will trap and direct any moisture that condenses on the
underside of the roofing material into rain water gutters.
I think that making interior surfaces more impermeable will only help trap
moisture in the walls, and would be against that.
Earth plasters, although brilliant at moderating humidity levels, are not
infinite sponges and do need to allow absorption to be reversed with
adequate ventilation.

Best,


Graeme,
Graeme North Architects,
49 Matthew Road,
RD1, Warkworth,
New Zealand 1241
Ph/fax +64 (0)9  4259305

www.ecodesign.co.nz






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