[GSBN] URGENT! Drying moisture out of SB walls
chris at endeavourcentre.org
Fri Apr 7 07:54:21 CDT 2017
It's not a cure-all by any means, but the silicate paints from
Canadian-based Perma-Tint (used to be Eco-House) have worked extremely
well for us: http://permatint.com/brick-staining-products/.
However, it's important to note that even a well-painted (or
rainscreened) bale wall is still susceptible to rain penetration at the
top of the wall and around all window/door framing. In every moisture
issue I've ever been asked to inspect, the bulk of the water entering
the wall is coming from a junction where plaster simply bumps into wood
or a window frame. It's astounding how much water can enter a 1/16
reveal-crack in a driving rainstorm...
On 2017-04-07 5:05 AM, Feile Butler wrote:
> 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 Ireland.
> 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 <mailto: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
> 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.
> */Martin Hammer, Architect
> /*1348 Hopkins St.
> Berkeley, CA 94702
> 510-525-0525 (office)
> 510-684-4488 (cell)
> From: Gsbn <gsbn-bounces at sustainablesources.com
> <mailto:gsbn-bounces at sustainablesources.com>> on behalf of Derek
> Roff <derek at unm.edu <mailto:derek at unm.edu>>
> Reply-To: GSBN <GSBN at SustainableSources.com
> <mailto:GSBN at SustainableSources.com>>
> Date: Thursday, April 6, 2017 at 6:18 PM
> To: GSBN <GSBN at SustainableSources.com
> <mailto: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 Roff
> derek at unm.edu <mailto:derek at unm.edu>
>> On Apr 6, 2017, at 6:21 PM, Paula Baker-Laporte FAIA
>> <paula at econest.com <mailto: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.
>> On Thu, Apr 6, 2017 at 2:19 PM, John Straube <jfstraube at gmail.com
>> <mailto: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
>> 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
>> 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.
>> > On Apr 5, 2017, at 7:42 PM, David Arkin, AIA
>> <david at arkintilt.com <mailto: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
>> > 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:
>> > * * * * *
>> > 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 1Ž2” 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)
>> > 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 <mailto:paula at econest.com>
>> Phone: 541.488.9508
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