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RE: GSBN:Moisture Problem



Hi, Paul·

 

Of course few of the sites where we build can be called extreme climates,
unless you call them extremely mild, so we havenât seen the occurrence of
wet patches you describe, but they do make sense. Iâve 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 weâre 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,

>I&#xE2;m 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.

>

>&#xE3;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&#xE4; of the bale, and into the plaster.&#xE4;

>

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

>

>&#xE3;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.&#xE4;

>

>It&#xE2;s 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 &#xE3;interior

>moisture sources&#xE4; isn&#xE2;t 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, wouldn&#xE2;t 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 &#xCE;climate&#xE2;,

>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 haven&#xE2;t seen the walls&#xB7;.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.gree";>mailto:%5bmailto:GSBN@...%5d"[mailto:GSBN@...

>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 wasn&#xE2;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&#xE2;ve spoken to Jim McSweeney, the owner, about

>what he found.  I&#xE2;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&#xE4; 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&#xE4; 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&#xE2;m not sure.)  The ceiling is

>&#xB8;&#xE4; 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 3-6&#xE4; of the walls, often in

>the range of 25-40%.  Unfortunately, I don&#xE2;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&#xE2;s, there were none in the 30&#xE2;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&#xE2;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&#xE2; 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 &#xE3;plaster

>adds a totally unacceptable amount of water to bale walls.&#xE4;  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&#xE2;t work in this climate.  I

>tried on that idea, but it doesn&#xE2;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&#xE2;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&#xE2;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&#xE2;ve been

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

>aren&#xE2;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&#xE4;~

>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&#xE2;t 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 aren&#xE2;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&#xE2;s repair project, that

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

>feel like I&#xE2;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

>

>

>--

>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

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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:

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

 

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For instructions on joining, leaving, or otherwise using the GSBN list, send
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