[GSBN] URGENT! Drying moisture out of SB walls
mfhammer at pacbell.net
Thu Apr 6 22:58:18 CDT 2017
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 hasn¹t 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 don¹t know exactly what the ³building paper² 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. David¹s idea of a 10¹ 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 don¹t know a perm
rating). I¹m 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. Wouldn¹t that pull the moisture to the
drier/warmer interior instead, or do I have my moisture mechanics backward.
Martin Hammer, Architect
1348 Hopkins St.
Berkeley, CA 94702
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
I¹m concerned that we don¹t 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 6² or further from the outside plaster. I¹m 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
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 won¹t 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
derek at unm.edu
> On Apr 6, 2017, at 6:21 PM, Paula Baker-Laporte FAIA <paula at econest.com>
> 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.
> 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 ³run for the hills² 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
>> 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 1x4¹s with
>> 45 degree sawn top edges over the lime plaster at, say 36² 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
>> More good pictures like that one sent would possibly help provide more ideas.
>>> > 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. I¹ve
>>> 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 CASBA¹s 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
>>> Economy². Registration is open: http://www.strawbuilding.org/event-2497515
>>> > * * * * *
>>> > I¹m 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 isn¹t 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 isn¹t 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 12² plywood to handle the bale weight. The wall assembly has
>>> 2-string rice straw bales laid flat, and is part of the building¹s 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 didn¹t 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 plaster2-layer building paper stapled to
>>> all wood framing, shingled to shed water, etc. The windows have sills, the
>>> 4¹ 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
>>> > 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 hasn¹t 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 roomsthe one with the
>>> most weather exposure (S. W. corner of building, labeled ³office² on the
>>> plans). I haven¹t 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. I¹m not familiar with
>>> the probe they used, but it¹s likely that the shaft is about 18² long, and
>>> if used as described to me, ³poked in a 45 degree angle from the interior of
>>> the wall near the outlets², probably penetrated about 5² into the wall when
>>> it reads 8², and about 12² into the wall where the chart says ³full in.²
>>> 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
>>> isn¹t 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 aren¹t as high as I would¹ve guessed based on your
>>> description that¹s 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 Hopland¹s 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 (it¹s
>>> a welcome pavilion¹) and once again it dried out promptly and has been
>>> > At the same time, I¹m 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. That¹s 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 10¹ 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. I¹m 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 EBNet¹s
>>> 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 aren¹t so high that invasive measures need to be
>>> taken. I¹d 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 I¹m
>>> more familiar with its application on cement stucco than lime, so research
>>> that a bit first. David Easton suggests Glaze ¹n¹ Seal on his earth walls.
>>> I believe both have that waterproofing effect while still remaining
>>> > 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
>>> can¹t 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 I¹d 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)
>>> > 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
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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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