[GSBN] URGENT! Drying moisture out of SB walls

Derek Stearns Roff derek at unm.edu
Fri Apr 7 20:00:59 CDT 2017

Thanks for all the additional information.  Given the additional moisture readings of 38% and 45%, I would want to try and dry the straw near the exterior plaster as quickly as practical.  I would use heat and air flow at the exterior surface.  In some situations, as Martin mentioned, there is a concern about heat (the sun) driving moisture in the plaster  deeper into a wall.  However, moisture always moves from wetter to dryer.  The only place where significant drying can occur quickly is at the outside surface of the plaster.  Heat plus airflow at the exterior plaster surface will remove much more moisture, much more quickly and effectively, than any alternative that I can think of.  The heat might drive a little moisture inwards for the first half hour, but after that, heat and airflow will pull moisture out of the wall.

I disagree with the concern about adding heat increasing the mold risk.  The wall is already in severe mold risk.  The listed temperatures in the wall, indoors, and outside all are sufficient to promote mold growth, if there is sufficient moisture.  And we know there is sufficient (excess) moisture.  If you could lower the temperature of the straw into the mid-30s Fahrenheit, or less, you could slow or stop mold growth.  That is not practical at this time of year.  If you could raise the temperature of the straw into the 80s or higher, these higher temperatures would slow mold growth a little.  That is possible, and it’s a good idea.  The 60s and 70s are the temperatures at which many molds grow best, especially plant decomposition molds.  We can’t win the temperature battle outright, and reduce the straw’s temperature to where the mold won’t grow at all.  We can increase the straw’s temperature a little, moving it out of the peak growth temperature range.  We can’t increase the temperature enough to prevent all mold growth, but somewhat higher temps, in themselves, help a little.  The only battle we can influence strongly is the moisture level.  Higher temps, combined with airflow, help a great deal in removing moisture and drying the plaster and straw, to a moisture content at which all mold growth will stop.

In summary, other factors are minor.  Through rapid drying, heat and air flow combine to provide the most effective way to address the mold risk caused by excessive moisture.

The use of vacuum cleaners was mentioned, to promote air flow in the straw.  This may help some, but the physics are against us.  In optimum conditions, a shop vac moves a fairly small volume of air, at a modest static pressure.  For example, figures that I found on the web indicate that a “6.5 peak horsepower Shop-Vac® vacuum rated at 9.3A at 120V produces 185 CFM (87 l/s) of airflow and 64 inches (160 mbar) of pressure.”  That’s very little air flow, and it can drop to ZERO, as you know, if you put your hand over the end of the hose.  Trying to suck air through the straw in a wall is not a lot different from putting your hand over the end of the hose.  Airflow drops very quickly with any increase in the resistance to air movement.  A cheap air compressor can produce 1000 times the pressure of a vacuum cleaner, so although it doesn’t move much air, when there is significant resistance to air flow, a compressor will move much more air than a vacuum cleaner.

Moving air inside a wall is hard to do.  It’s probably worth trying but a big piece of the drying strategy should be moving a lot of warm, dry air over the exterior surface of the plaster.  With fans or blowers, you can move thousands of cubic feet per minute over many square feet of surface area.  Adding radiant heat from halogen lights or other sources will raise the temperature and lower the relative humidity of the moving air.  This gives the chance for a lot of moisture removal pretty quickly.


Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

On Apr 7, 2017, at 1:57 PM, David Arkin, AIA <david at arkintilt.com<mailto:david at arkintilt.com>> wrote:

Hello Worldwide Team:

Here’s an update, and also my proposal we add Oregon Builder and CASBA Workshop Instructor Jim Reiland as an active member of our Network.  He’s advising the owner and contractor in this particular situation.  The website to his company, Many Hands Builders, is below.  Jim is the lead editor of CASBA’s effort to rewrite our Detail Guide.

Thanks ALL!  — David Arkin

WOW!  I woke up this morning to this outpouring of response—thank you  David!   And yes, I’d be honored to be nominated to be a posting member.  If you need anything from me to move that process forward, let me know.

Here’s an update:

RE: question about building paper.   This building has both 60-minute and 30-minute two-ply Grade D paper over wood framing only, lapped a few inches (4” – 6”) over adjacent bale surfaces, all shingled to shed liquid moisture that makes it through the lime plaster.   Note: In talking with a handful of plasterers I gather there are two schools of thought on the paper lap.  Some wrap framing with paper prior to installing bales (no lap over adjacent bale surfaces), and others lap it over adjacent surfaces by 4” – 6” post bale raising.   I’m in the latter group—since green lumber is used in a bales-laid-flat wall system, I lean towards lapping in the belief it offers a better slip plane to prevent telegraphing cracks as the green wood loses moisture.

Recognizing the limitations of probing the wall cavity from the back of electrical outlets, the general contractor cut a 4” x 4” hole in the exterior wall where they believe they had the most moisture in the wall.  See photo.


They probed into the wall, as-well-as reached in to feel around, pull out straw to evaluate, and confirmed that indeed the moisture is concentrated near the exterior few inches of the wall, immediately behind the plaster.   As this hole was cut near a post, they were able to determine that the straw behind building paper is much drier than straw with no paper protection.   They measured 35% moisture near the exterior surface, and 14% at the interior surface.   In other locations accessed from the interior, probing directly to the exterior plaster they recorded 38% and 45% moisture.   From the owner:  “straw near the exterior surface was clearly moist if not actually wet.  It was dark, blotchy with dark spots (mold?!), smelled, and was crumbly.   Somewhere past about 8” the straw that was not wet, nor crumbly and smelled like a fresh bale more or less.”

On this building the lime plaster plays a shear role, and except where paper laps over bale surfaces, was well keyed into the bales, embedding 17 gauge galv. lath during the scratch coat application.

They set up a heat lamp (to simulate a dry, sunny day) and shop vacuum suction system to evaluate the drying around this 4” x 4” opening.  See photo.   No report on this yet.    But this raises the question Marty posed about getting the moisture mechanics right—in this situation, does moisture move towards, or away from a warm, dry surface?   The house interior humidity is kept at 19%.  The house temperature has been kept at a constant low-mid 70s (F) through the winter.  The exterior temperature ranges from high 40s to low 60s (F), and humidity ranges down from 100%.  Very, few “dry” sunny days this time of year.


Interior wall temperatures obtained by probing through electrical outlets throughout the building range between 72 and 78 degrees.   There doesn’t appear to be a strong correlation with higher moisture and higher temperature—several probe locations read 72 degrees, but had 12%, 17%, 24% moisture.   Another factor accounting for the differences might be solar radiation—in general, the south facing wall has both the highest moisture readings, but also receives what sun they get.   I’m inclined to think the slightly elevated temperatures are less an indication of  “hot spots” in bale wall in the process of decomposing, and more influenced by either interior temperature or sunshine, but if the moisture remains for much longer….

Two sources—a restoration company specializing in drying out wall cavities (but no experience with straw bale walls), and a mold expert, have advised against applying heat to either side of the wall—they fear it would raise interior wall temperatures, hasten decomposition, and encourage mold growth.

I asked the GC and owner to open additional access ports in the exterior wall once it’s protected from wind-driven rain, both above and below the existing port (3’ above FF), and near where they first detected an odor.  It also appears to be the wettest exterior wall surface.   To learn more about the scope of the problem I also asked if they’d open holes in other exposed wall locations.

Any guidance you can offer on the question of where to apply heat/moving air would be appreciated!


Jim Reiland
Many Hands Builders
541-200-9546 cell
jim at manyhandsbuilders.com<mailto:jim at manyhandsbuilders.com>

On Apr 7, 2017, at 11:29 AM, Martin Hammer <mfhammer at pacbell.net<mailto:mfhammer at pacbell.net>> wrote:

Good point Derek, and after reading it again I agree with you that the building paper likely covers only the framing. But it would be good to have that confirmed. I first interpreted it as the paper covering the entire wall.


PS - I’ll add a partial email from a colleague who receives GSBN posts as a reader only:

A temperature probe may be a relatively simple way to test whether bales are rotting.  The microbes create a lot of heat, and if it's warmer in the wall than inside or outside you've got some bad action.

That's how I realized we had a problem at Shorebird [a public SB building] - . . ., reaching in the bale wall I could feel the heat.


Greg VanMechelen
VanMechelen Architects
732 Gilman Street
Berkeley, CA 94710
510.558.1075 510.558.1076 (fax)
greg at vanmechelenarchitects.com<mailto:greg at vanmechelenarchitects.com>

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: Friday, April 7, 2017 at 6:40 AM
To: GSBN <GSBN at SustainableSources.com<mailto:GSBN at SustainableSources.com>>
Subject: Re: [GSBN] URGENT! Drying moisture out of SB walls

I’m wondering about the two possible interpretations of the sentence describing the building paper.  "The wall was prepped to receive a lime plaster—2-layer building paper stapled to all wood framing, shingled to shed water, etc”.   Does this mean that the paper covers only the wood, or does the paper cover the bale surfaces as well, spanning the bales from wood framing piece to wood framing piece?  I’m thinking it’s the former, and that the lime plaster is keyed into the straw of the bales.  But some other comments have indicated the other alternative.  David Arkin, can you clarify this detail for us?


Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

On Apr 7, 2017, at 6:54 AM, Chris Magwood <chris at endeavourcentre.org<mailto:chris at endeavourcentre.org>> wrote:

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>

----- 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.



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.  http://www.keimpaints.co.uk/about_us/comparison_of_keim_mineral_paints_and_limewash/

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 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.


> 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 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 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
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