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GSBN:More moisture problems - Southern California

Good day all,

Sorry for some cross-posting to a couple of other lists.

Like the Straw Wolf and Danny Buck, we have a real problem with "moisture" in the walls of a project in our area. No, it isn't one of mine, but it is this kind of "problem" that can give Straw Bale Construction a bad name, so it is everyone's problem.

I do remember the exchanges regarding the SB that Danny was working on, but was kicking myself because I hadn't saved them - Thank you Joyce for "reminding" me that it had been reprinted in issue #49 of TLS, and thank you all for your extremely valuable insight and sharing your experiences. If we can actually root out the sources of the moisture, and come to some conclusions, I hope to be able to write some sort of analysis and summary for future reference. I think your past and future input on the subject will be invaluable. ~bb


This is a large home (3,000 Sf) with lots of amenities, and the parapet style is consistent with other projects by the same Architect. 


This year was one of those few "wet" years that we have, and in the area of the project, (Ramona, San Diego County, CA - USA) the rainfall for the season was ~25 inches; the 2nd highest on record. Some of the rains were very heavy downpours and much of those were wind-driven directly into the South and West-facing parapet walls.

Several items of particular note: Water was detected dripping out of the kitchen soffit after only 1-1/2 days of rain, and moisture content readings, principally grouped in 6 different locations, were recorded at +- 40% within the center of the bales. Other reading surrounding the affected areas ranged between 15 and 20%. While the current readings indicate some areas were wetter than others, I believe (speculating) that the leakage occurred pretty much all along the parapet walls on the South and West sides of the house. There were wet walls elsewhere, but perhaps they were caused by different problems. The architect just reminded me that there were also quite a few wet spots in the wood-framed portions of the home, which makes this even more interesting.

All window and door opening were sealed with bituminous material between the openings and the frames. I have been told that a moisture barrier was used to cover the wooden parapets and lapped over the bales. 

The plaster was a 3-coat cement stucco - I am still investigating whether lime was used in the mix, but it seems unlikely. It seems more probable that the plaster was more of a moisture barrier than a likely source as the point of water entry. No sealer was applied to the stucco. There is some cracking, both horizontal and vertical, and while a few are potentially large enough to allow water into the bale interior, at best they could only account for some of the water at some locations. There are also hairline cracks; and I guess the thinking is that the rainfall may have penetrated all 3 plaster layers. 

The framing details on the plans don't really tell me a lot about the construction of the parapet, other than it seems to be an extensions of the posts, and I am assuming that it was sheathed, papered, lathed and plastered. The roofing detail sheet is a cookie-cutter and doesn't even illustrate a parapet of this type.

I have compared notes with Mark Tighe, another experienced bale builder and who also examined the house - each of our independent investigations lasted about 3 hours. We both came to pretty much the same conclusion that nothing that we could see would account for all of the water that appears to have entered the wall up around the (wooden) parapet extension. There was at least some penetration there because there were consistent wet readings all along the top of the walls at the ceiling. We can't tell how much entered there or how much may have entered down the wall.

It has been suggested that where the first water was spotted, one potential scenario is that water penetrated the stucco (from where is yet unknown) and ran down the inside face of the interior plaster until it hit the box beam kitchen soffit, where it poured into the soffit and out the light fixture. This might account for the kitchen leak, but in the few plastered test walls that I have (struggled to) removed the plaster from, there wasn't what you would call a lot of room for water to travel through very rapidly. Also, how would the water get to the interior plaster surface? Water doesn't flow very well across bales.

To make this all a bit more interesting, the owner has grasped onto the idea of installing a sheet moisture barrier between the plaster and the bales when the time for repair comes (not that I blame him at this point). I and others (and he has read) have explained that this is likely to cause moisture to be trapped within the cavity and in itself cause rot. He said that he had heard that, but has yet to see evidence that is really true. Not that is shakes my faith in the truth of the supposition, come to think of it, other than from the Straw Wolf, neither have I, though John Straube has published some very convincing test data that certainly makes the case.

My next step is to contact the contractor, that is now out of state, and see if they can give some insight as to the potential failures. I have requested that the owners create a grid of test holes from the inside, where the others are, and really see if we can figure out just where and how widespread the problem really is.

I feel for these folks, fearing the worst (whatever that is) and about to watch parts of their house being demolished. Not happy campers and I know that everyone feels badly.

I would appreciate hearing your thoughts on the subject. 

At the moment, the owners are pretty upset that they are in this position, and are now questioning anyone's point of view unless there is documented evidence to back the assertions up. I can't fault them for that.

Their questions are as follows - please do what you can to provide some sort of documentation and/or experiences supporting your thoughts. 


1) Do parapet walls "always" allow moisture penetration? Any experiences or testing that might indicate why some did and others didn't?

2) Does 3-coat cement plaster (stucco) allow enough water to penetrate a wall and substantially "soak" the bales? I seem to recall that Dr. Straube's tests involved capillary uptake, but I don't think that if I had the rest results in front of me I would necessarily understand them without a really clear explanation. How would this compare to rainfall on a vertical wall surface?

3) Will a sheet moisture barrier between the bales and the plaster cause the bales to decompose?

4) Will a non permeable stucco function the same as a sheet moisture barrier and cause the bales to decompose?

5) Is there any rule of thumb that would give us an indication that over that moisture content % the bales won't likely dry out, but under that % they will likely dry out. I understand that is a "difficult" question because much will depend on the drying conditions, but I was wondering if someone had reached some conclusion made from personal observation in their experiences.

I will pass on any developments as I can.


My thanks in advance for any insight, experiences, information on other failures and documentation of the causes. If at all possible, I am in hopes that we will be able to pass on any information that will assist those in the future make "better" and informed decisions.



Bob Bolles
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