[GSBN] URGENT! Drying moisture out of SB walls

Martin Hammer mfhammer at pacbell.net
Fri Apr 7 06:34:28 CDT 2017

Hello again,

Good point by Feile (hi Feile) about the battens for the rain screen. They
need to be vertical (to allow unimpeded vertical ventilation) which then
means horizontal lap siding, if boards are used for the cladding. The
horizontal orientation for the siding is also better than vertical for
shedding rain (if lapped, or T&G with the tongue up).

I agree with Feile about the smell. Until we’re able to transmit smells via
the internet I’ll say that the words “smelled something awful” is a clear
indication that somewhere in the vicinity there’s rotting straw (unless I
suppose there’s dead rodent?).

One other comment is I was impressed by the report and descriptions by the
CASBA member. Very thorough and articulate.

One last comment, as prompted by Feile. Upward driving rain?! Wow.


From:  Gsbn <gsbn-bounces at sustainablesources.com> on behalf of Feile Butler
<feile at mudandwood.com>
Organization:  Mud and Wood
Reply-To:  Feile Butler <feile at mudandwood.com>, GSBN
<GSBN at SustainableSources.com>
Date:  Friday, April 7, 2017 at 2:05 AM
To:  GSBN <GSBN at SustainableSources.com>
Subject:  Re: [GSBN] URGENT! Drying moisture out of SB walls

Hi All
Throwing my tuppence into the mix from the Emerald Isle - famously green due
to our impressive levels of rain.
While you may succeed in drying out the walls, the weather will keep on
doing what it does ... and with climate change, it will only get worse. We
are definitely noticing an increase in frequency/intensity of winter storms
and in wetter summers here (oh joy!). In our practice, we never specify lime
applied directly on to bales. It just cannot cope with the external moisture
loads inflicted on it. There are too many stories of rotting bale walls in
While there has been some discussion that the moisture levels recorded in
these bales are not over concerning (yet), the fact that there is an
appalling smell is a pretty good indicator that all is not well (as long as
other sources have been ruled out).
Martin mentioned the building paper and that we don't know what it is. We
have heard reports of buildings where the construction moisture levels were
so high, that micro-porous breather membranes were overwhelmed by the amount
of water vapour trying to pass through as the building dried out and
basically self-sealed .... thereby creating a situation where moisture
became trapped in the building - not good. This has been reported a few
times for roof construction, not for walls. But there is no reason why it
might not be happening in walls - it is just much more obvious when you are
sitting in an attic space and drips are rolling off the membrane. So when we
can, we specify cellular membranes like Intello - which act by osmosis (and
can reverse direction of vapour flow depending on vapour pressure loadings
internally and externally), rather than the micro-porous membranes.
I would recommend adding a rain screen, as advised by John and others. In
Ireland, we design to keep the rain out and then we design another line of
defence for when the rain breaches the first detail ..... and we have to
design for horizontal and even upward driving rain.
If this building was in Ireland, I would recommend drying it out by whatever
means necessary. If it means pulling off the lime render, then so be it and
I would then wrap the bales externally with a cellular-based membrane (if
the clients can afford it). If they can dry out the bales without removing
the lime, then this should be adequate as the second line of defence and the
addition of the cellular membrane would not be necessary.
If they want the appearance of a solid render, rather than timber boards,
then I would fix 50mm vertical battens to the dried-out bales (covered with
lime or with an appropriate membrane) to form a drainage channel and
ventilation space. Then apply render carrier boards. Ensure that ventilation
is retained at the top and bottom of these boards. To save money, as there
is a ventilated cavity behind, these can be cement based (i.e.they don't
need to be breathable). Or the client can go full eco if they can afford it.
Install anti-vermin steel mesh at the bottom, but ensure that the cavity is
still ventilated and can drain out. Then apply lime render to the boards.
Use a good multi-direction mesh where the render boards connect back into
the other elevations.
If the clients are happy to have vertical timber boards, I would still
install 50mm vertical battens behind the horizontal battens (fixings for the
vertical boards). Having a clear flowing drainage cavity (uninhibited by
horizontal battens) is key to keeping the rest of the building dry.
As the overhang is reasonable, you should not need to extend the roof, as
this detail can take a whole heap of rain. Only the window reveals and cills
will increase. I recommend a min. 50mm overhang for cills to throw rain off
the wall below.
Feile Butler
feile at mudandwood.com
www.mudandwood.com <http://www.mudandwood.com>
> ----- Original Message -----
> From:  Martin  Hammer <mailto:mfhammer at pacbell.net>
> To: GSBN <mailto:GSBN at SustainableSources.com>
> Sent: Friday, April 07, 2017 4:58 AM
> Subject: Re: [GSBN] URGENT! Drying  moisture out of SB walls
> Hi all,
> I agree with Derek that the straw close to the exterior could have a  moisture
> content significantly higher than the readings provided. Especially  near the
> bottom of the wall. I suggest the owners obtain a longer probe or  drill holes
> in at least a few places in the exterior plaster in the bottom  third of the
> wall to take readings for the first few inches of straw. Enough  to get a clue
> about the highest moisture content of the straw in the  walls.
> One fact about the wall assembly that hasn?t been mentioned by the GSBN
> moisture sleuths is that it has two layers of building paper between the
> plaster and the bales. This could be a benefit (allowing less water that has
> penetrated the plaster to reach the straw) or a detriment (inhibiting the
> release of moisture in the straw to the outside air, depending on its vapor
> permeability). And we don?t know exactly what the ?building paper? is. I
> imagine that if water penetrated the plaster, and if the paper was installed
> properly, almost all of that water would be stopped by the two layers of
> paper, except maybe at fastener penetrations or tears in the paper. Gravity
> should then pull the water down and out, but only if there is sufficient means
> of safe escape at the bottom of the paper/plaster.
> A four foot overhang is substantial, but apparently not enough for this
> exposure/climate. David?s idea of a 10? porch overhang certainly is one way to
> solve the problem. Or an exterior cladding suggest by Derek and John. Or
> regarding water repellent, colleagues in northern California have claimed
> success using siloxane over lime or cement-lime plaster on straw bale walls.
> It repels water but maintains good vapor permeability (I don?t know a perm
> rating). I?m not sure if has been used successfully over clay paster.
> One other thought is regarding the use of heat on the interior to drive
> moisture to the exterior. Wouldn?t that pull the moisture to the drier/warmer
> interior instead, or do I have my moisture mechanics backward.
> Cheers,
> Martin 
> Martin  Hammer, Architect
> 1348 Hopkins St.
> Berkeley, CA   94702
> 510-525-0525  (office)
> 510-684-4488  (cell)
> From: Gsbn <gsbn-bounces at sustainablesources.com>  on behalf of Derek Roff
> <derek at unm.edu>
> Reply-To: GSBN <GSBN at SustainableSources.com>
> Date: Thursday, April 6, 2017 at 6:18  PM
> To: GSBN <GSBN at SustainableSources.com>
> Subject: Re: [GSBN] URGENT! Drying moisture  out of SB walls
> I?m  concerned that we don?t have enough data on current moisture levels near
> the  exterior of the wall.  If rain has entered the straw through the exterior
> plaster, because of the extreme wind and rain, the straw might be several
> percentage points wetter in the first few inches under the exterior plaster
> skin.  As I understand the moisture testing done so far, the readings  have
> been taken from the inside, and the probe probably never got closer than  6?
> or further from the outside plaster.  I?m sure that there is a desire  to
> avoid adding visible holes/patches to the outside plaster, but if this
> hesitation leads to severe decay in the straw, that is obviously a poor
> trade-off.    
> One thing we can be certain of is that extreme, nearly horizontal rain  has
> been hitting these walls.  This year may have been worse than  average, but it
> is poor strategy to suppose that the same or worse won?t  happen again in
> other years.  That suggests that a physical barrier is  needed to protect
> these walls, along the lines of the ventilated rain screen  that John Straube
> described.  The probability, and in my view, the  certainty, that the exterior
> plaster needs to be covered, ought to decrease  the worries about drilling a
> few holes in the exterior plaster, in order to  take additional moisture
> readings.  
> Derek
> Derek Roff
> derek at unm.edu
>> On Apr 6, 2017, at 6:21 PM, Paula Baker-Laporte FAIA <paula at econest.com>
>> wrote:
>> We have used Keim liquid silicate coatings over earth plasters  in an area
>> that was very susceptable to erosion from driving rain and had  great success
>> with it. They make many different products and do a lot of  restorations with
>> it in Europe and so I imagine they have a solution to use  over lime.
>> Coatings are clear or pigmented. They can also do very exact  color matching
>> if a sample is sent to them.
>> http://www.keimpaints.co.uk/about_us/comparison_of_keim_mineral_paints_and_li
>> mewash/
>> On Thu, Apr 6, 2017 at 2:19 PM, John Straube <jfstraube at gmail.com> wrote:
>>> Hi all
>>> Interesting case because it looks like they  did almost everything
>>> correctly. I am sorry to hear of their bad luck. The  photo is quite
>>> telling, but I do wonder how the rain is getting in   at that angle (other
>>> than stupidly high levels of wind)
>>> I agree with  you Dave that the numbers are not ?run for the hills? but they
>>> are  worrisome.
>>> Definitely worth checking for any of the obvious bulk water  flaws and being
>>> more careful and complete in your MC  measurements.
>>> I can be certain of one thing ? there is definitely  an amount of rain that
>>> will over whelm the lime plaster, and cause wetting  of the straw.  That
>>> amount depends on the drying potential of the  climate and the lime plaster
>>> thickness and properties.  Nothing magic  about lime, it is just better than
>>> cement, and much better than  unite.
>>> It is expensive and invasive to  dry the wall by  drilling holes and blowing
>>> dry air.  The hard part is the machine  with dry air (desiccant driers are
>>> available from flood restoration  companies).  One could simply blow heater
>>> air into holes? easier,  still annoying.
>>> I would consider hanging a dark coloured (to collect  solar heat) tarp or
>>> geotextile from the overhang edge/gutter to the grade  to act as a highly
>>> ventilated (critical), rain screen.  This will  stop further wetting and
>>> along drying.
>>> Also, adding heat to the inside  will be helpful: increases the interior
>>> temperature where wetness is  evident by even 5 degrees will help, although
>>> a steady and spatially  uniform 10 or more will really make a difference in
>>> a matter of  weeks.  I know people who have used arrays of heat lamps, plug
>>> in  electric heaters with the door closed, and stoked up wood stoves to
>>> drive  moisture out of walls.
>>> If the MC can get below 20% or so, then I  think you have a lot of time to
>>> design an upgrade? almost all coatings  have limits and are not as good as a
>>> real over clad.  Xypex is a pore  blocker (hence reduces vapor permeance)
>>> that reacts with alkalinity to  form calcium silicates.  Could work well
>>> with fresh lime, but  probably wont work well with the exterior carbonated
>>> surface of the  lime.  I would be quite skeptical of most coatings? products
>>> like  Silanes certainly work and can make a pretty big difference, we just
>>> dont  know if they make enough of a difference.
>>> If acceptable, it is  pretty cheap and simple to install horizontal 1x4?s
>>> with 45 degree sawn  top edges over the lime plaster at, say 36? on centre
>>> or so, then add  vertical boards with generous joints.  Or add vertical 1x4
>>> and  clapboard siding (much more effective at rain shedding).  This will
>>> reduce the wetting by a factor of 10 or more, and only slow drying by a  bit
>>> (if well ventilated) so a pretty massive improvement and certain to  solve
>>> driving rain problems (if that is what this is).
>>> Planting a hedge  and some trees a dozen yards upwind would also be a good
>>> idea.
>>> More  good pictures like that one sent would possibly help provide more
>>> ideas.
>>> John
>>>> > On Apr 5, 2017, at 7:42 PM, David  Arkin, AIA <david at arkintilt.com>
>>>> wrote:
>>>> >
>>>> > Hello Global Balers:
>>>> >
>>>> >  A CASBA  member poses the questions outlined in the situation below.
>>>> I?ve  attached my responses below the query and photo, and invite any of
>>>> you to  weigh in with further recommendations, follow-up questions or
>>>> anecdotes  that may be useful.
>>>> >
>>>> > Best,
>>>> >
>>>> > David Arkin,  AIA, Director
>>>> > California Straw Building  Association
>>>> >
>>>> > ps: Joins us for CASBA?s 2017 Spring  Conference, May 5-7 in the San
>>>> Francisco Bay Area, featuring architect  Craig White of the U.K.:  "Towards
>>>> a Photosynthetic Architecture -  Renewable Buildings for the Circular
>>>> Carbon Economy?.    Registration is open:
>>>> http://www.strawbuilding.org/event-2497515
>>>> >
>>>> >  *  *  *  *  *
>>>> >
>>>> > I?m  hoping you can  address some of my questions or direct me to anyone
>>>> with experience  dealing with this problem, or anyone who has any insights
>>>> into causes and  solutions.
>>>> >
>>>> > I was contacted this morning by a client just  south of Portland who has
>>>> measured high levels of moisture in their straw  bale walls, and is asking
>>>> for advice on how to deal with the  problem.
>>>> >
>>>> > The core questions I have are  these:
>>>> >
>>>> > 1.       Assuming there isn?t a  bulk water leak from the roof,
>>>> downspout, or window, can wind-driven rain  account for high levels of
>>>> moisture in a straw bale wall assembly?   In other words, what does it take
>>>> for a properly installed lime plaster to  be overwhelmed by wind-driven
>>>> rain?
>>>> >
>>>> > 2.        What are the options for drying the wall out?   Waiting  for
>>>> dry weather (summer!) may not  be an option as wet straw bales  may not
>>>> survive that long.
>>>> >
>>>> > 3.        Once the wall is dried out, assuming there isn?t significant
>>>> permanent damage to the bales, what surface treatments are available that
>>>> would prevent liquid moisture from soaking into the walls, yet keep them
>>>> vapor permeable.   I can imagine several landscaping and rain  screen
>>>> (siding) solutions, but am not familiar with surface  treatments.
>>>> >
>>>> > Background Information.
>>>> >
>>>> >  Details about the wall assembly.   The SB walls are on a raised  floor.
>>>> The space between the sill plates was filled with rock  wool insulation and
>>>> capped with 1?2? plywood to handle the bale  weight.  The wall assembly has
>>>> 2-string rice straw bales laid flat,  and is part of the building?s shear
>>>> wall system, using 17 gauge lath and  lime plaster (exterior and interior).
>>>> Instead of applying a  finish coat of lime plaster the client chose to
>>>> apply a lime based paint  from BioShield.    I didn?t plaster the structure
>>>> or apply the  lime paint, but believe it was done by capable professionals
>>>> in accordance  with best practices.  The bales were stack in April-May of
>>>> 2016.   Bale wall moisture readings just prior to plastering  averaged
>>>> 14.1%.   The wall was prepped to receive a lime  plaster?2-layer building
>>>> paper stapled to all wood framing, shingled to  shed water, etc.  The
>>>> windows have sills, the 4? roof overhangs are  guttered and the downspout
>>>> installed properly.   The walls were  plastered during late spring and
>>>> early summer.   Three coats of  exterior lime paint were applied in late
>>>> summer-early fall.     When I visited in November, I saw vertical cracks at
>>>> the corners only  (where I always see them, regardless of how much
>>>> corner-aid or exp. metal  lath is underneath!).
>>>> >
>>>> > Building site.  The house is  located in an open field and has no
>>>> barriers to wind driven rain.     The general contractor, who happens to
>>>> live next-door, told me the  field is like a wind tunnel.  He reported that
>>>> since it began raining  in the fall of 2016 he hasn?t seen the walls look
>>>> dry more than a dozen  times.
>>>> >
>>>> > The problem first came to my attention about a  month ago when the client
>>>> told me they smelled something awful in one of  their rooms?the one with
>>>> the most weather exposure (S. W. corner of  building, labeled ?office? on
>>>> the plans).   I haven?t visited  the site, but advised them to first
>>>> investigate and rule out all the other  likely possible causes for an odor
>>>> (e.g. decomposing straw piled near the  house, something else rotting in
>>>> the crawl space, etc.), and if the odor  persisted, to gather quantifiable
>>>> information, including using a moisture  meter probed into the wall near
>>>> outlets, which they have now done, (see  below).
>>>> >
>>>> > <image001.png>
>>>> >
>>>> >
>>>> >  <image002.png>
>>>> >
>>>> > The office is in the S. W. corner of  the structure.  I?m not familiar
>>>> with the probe they used, but it?s  likely that the shaft is about 18?
>>>> long, and if used as described to me,  ?poked in a 45 degree angle from the
>>>> interior of the wall near the  outlets?, probably penetrated about 5? into
>>>> the wall when it reads 8?, and  about 12? into the wall where the chart
>>>> says ?full in.?  From all the  points they gathered data, moisture readings
>>>> were higher towards the  exterior of the wall.
>>>> >
>>>> > My understanding is that lime  plasters will absorb and then release
>>>> liquid moisture from wind driven  rain, and are quite able to handle
>>>> regular, frequent wettings without  compromising the straw beneath.   If
>>>> bulk water isn?t entering  the wall through a breach in the flashing or
>>>> another leak of some kind, is  it possible that an unusually wet winter (I
>>>> believe the Willamette Valley  is experiencing a well-above average
>>>> rainfall year like much of the west  coast) could create the moisture
>>>> levels seen below?   Is it  possible that the  water is soaking in, and
>>>> just keeps soaking in,  unable to dry out because of the constant rains?
>>>> > <wind driven  rain on lime plastered SB wall, S exposure..jpg>
>>>> >
>>>> >  *  *  *  *  *
>>>> >
>>>> > [Arkin comments in  reply]
>>>> >
>>>> > The moisture readings aren?t as high as I would?ve  guessed based on your
>>>> description ? that?s perhaps good news.  We had  a wall at the Real Goods
>>>> Solar Living Center that was an exterior site  wall with very little
>>>> overhang, and it would get pounded by the  rain.  We had a moisture reading
>>>> over 50%!  However, in  Hopland?s sunny hot climate it dried out between
>>>> rains and now with a new  broad overhang it is doing fine, 20+ years later.
>>>> Similarly a small  outbuilding on that same site was flooded to the middle
>>>> of the second  level of bales.  It was earth plastered and we advised to
>>>> simply let  it be and see what happens.  The building has no windows or
>>>> doors  (it?s a ?welcome pavilion?) and once again it dried out promptly and
>>>> has  been fine.
>>>> >
>>>> > At the same time, I?m recalling an olive oil  facility that was on top of
>>>> a hill in San Luis Obispo County, that had  wind-driven rain penetrate
>>>> cracks in the Gunite finish on their bale  walls, to the point of black goo
>>>> oozing out the base.  That?s when  you know you have real trouble.  They
>>>> drilled holes and drove air  into the bottom of the walls, and also put a
>>>> layer of breathable  waterproofing on the exterior of the walls.  Similar
>>>> to your case  here, it was the windward side that had the worst problems,
>>>> but rain  swirling around the building caused some issues on the leeward
>>>> side  too.
>>>> >
>>>> > Here are my opinions on your questions, but let me be  the first to admit
>>>> there are others who could answer these better than  me:
>>>> >
>>>> > 1.  The photo sure makes it look like wind driven  rain, and at quite an
>>>> angle!  Another 10? of overhang (aka a porch)  along that facade seems in
>>>> order. Exactly how much moisture it takes to  overwhelm a lime plaster wall
>>>> is difficult to say.  I?m recalling  studies done by the University of Bath
>>>> that placed plastered wall samples  in very exposed marine climates to
>>>> determine this.  You might search  for this, perhaps starting with EBNet?s
>>>> BuildWell Library.  Bruce  King may be able to connect you with Pete
>>>> Walker, or you could try to  reach him directly.
>>>> >
>>>> > 2.  Again, the numbers aren?t so  high that invasive measures need to be
>>>> taken.  I?d suggest putting  some more powerful heaters on the interior,
>>>> and aim to drive the moisture  out toward the exterior.  At the same time
>>>> they should deploy tarps  or some other means of keeping wind driven rain
>>>> off the walls going  forward, but let the sun and warmth at them otherwise.
>>>> >
>>>> >  3.  Again, my first suggestion is a longer porch roof along that  whole
>>>> facade, perhaps with some landscaping or something to break up the  laminar
>>>> wind.  I suppose a deployable system of a rain screen of some  sort could
>>>> also be used.  Allowing the walls to see sun this spring  and summer will
>>>> be good though.  Xypex is a product that folks have  applied to walls, but
>>>> I?m more familiar with its application on cement  stucco than lime, so
>>>> research that a bit first.  David Easton  suggests Glaze ?n? Seal on his
>>>> earth walls.  I believe both have that  waterproofing effect while still
>>>> remaining breathable.
>>>> >
>>>> > As  you know, both the plaster and the straw have a significant capacity
>>>> to  store and release moisture, and it seems they are doing exactly  that.
>>>> I can?t say for certain, but this being their first season  they may not be
>>>> damaged to the point of needing to be replaced, but the  smell detected is
>>>> concerning.  Getting them to dry and then keeping  them dry going forward
>>>> is key, and if necessary some replacement may be  needed, but I?d advise
>>>> trying to avoid that first.
>>>> >
>>>> > *   *  *  *  *
>>>> > Arkin Tilt Architects
>>>> > Ecological  Planning & Design
>>>> >
>>>> > Please Support (or Join?!) my 2017  Climate Ride (bicycling 300 miles
>>>> from SF to SLO, June 9-13, with a  fundraising goal of $5,000 to support
>>>> Straw-Bale outreach)
>>>> > 
>>>> http://support.climateride.org/index.cfm?fuseaction=donorDrive.participant&
>>>> participantID=4497
>>>> >  Thank you!
>>>> >
>>>> > David Arkin, AIA, Architect
>>>> > LEED  Accredited Professional
>>>> > CA #C22459/NV #5030
>>>> >
>>>> > 1101  8th St. #180, Berkeley, CA  94710
>>>> > 510/528-9830  ext. 2# <tel:510%2F528-9830%20ext.%202%23>
>>>> > www.arkintilt.com <http://www.arkintilt.com/>
>>>> >
>>>> > "There is no way to  peace. Peace is the way."
>>>> > ? A. J.  Muste
>>>> >
>>>> >
>>>> >
>>>> >  _______________________________________________
>>>> > Gsbn mailing  list
>>>> > Gsbn at sustainablesources.com
>>>> >  http://sustainablesources.com/mailman/listinfo.cgi/gsbn
>>> _______________________________________________
>>> Gsbn  mailing list
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>> -- 
>> Paula Baker-Laporte FAIA,BBEC
>> Econest Architecture Inc.
>> www.EcoNest.com <http://www.econest.com/>
>> paula at econest.com
>> Phone:  541.488.9508
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