Curious as to what the experts have to say on this. I am confused about vb's and permeability of the insulation and walls. I always though at least a quick slip spray was needed on straw no matter what.
I gave the linked site a quick scan, and as soon as I saw straw bale insulation and then a foam, which is a non-permeable or low permeable layer in the matrix, I don't give the long term durability of the structure much hope.
Architecture in general actually needs to be permeable (or breath as many describe it) and the entire concept of "air tight" buildings is just that...a concept. Its track record is less than 50 years old and the preliminary evidence that many us are seeing is it doesn't work. It has never worked with natural building materials in any example I have ever gotten to see forensically.
In my experience and view...a wall with the following design matrix...
5/16-inch thick, textured, painted, fiber cement siding, screwed into
flat-faced 2x4's at a 24-inch spacing, directly touching
side-stacked straw bales, with a thickness of 14 inches, directly against
1/2" sheets of foil-faced foam insulation (with the inner face foil-taped to make a vapor barrier), touching
flat-faced 2x4's at a 24-inch spacing, directly touching
1/2-inch gypsum wallboard, covered with a 1/16-inch layer of joint compound, textured with a rubber roller, and painted with a zero V.O.C. latex paint.
...is destine to have issues over time. The interstitial zones of these walls become unobservable, and inevitably have moisture buildup do to restricted permeability by all the non-breathable layers. In this case moisture, during certain times of the year, will move into the SB and not be able to migrate effectively enough to mitigate the issues associated with high moisture content in walls...like molds and decay. Also, any system that is meant to "stop" moisture from moving (like the foam) never achieves that goal...It only slows the process way, way down, and therein lies the problem. If the builders had at least left a 30mm air gap between the SB and the foam, it may have lessened the evidable moisture build up. To make issues even worse...a modern latex paint is used which is never as permeable as traditional paints and never as permeable as manufacture claim.
Overall, many of these "new age" types of structures, built in this fashion, may last decades without noticeable issue. The questions is what they will look like (or be like) in a generation or two (i.e. couple hundred years)...This the real issue. I still don't understand why so many builders insist on ignoring good practices in means, methods and materials, with long proven records to instead experiment with "concepts." I am all for experimentation and testing concepts...however, when I build something to live in or for a client...I want as many aspects of the build as possible to be fully understood and with the longest histories of empirical knowledge backing it up. Architecture is to costly in time and money to "experiment with." I hope some of the "new concepts" prove to be worthwhile...Thus far in my experience few (if any?) have...
Thanks jay, i honestly wanted to title this post, what does jay think. I figured something just wasn't right. My second question is, what is your opinion on light straw clay fill, with wooden siding? This is the option i like the most, with a good stone facade for extra boot protection against splash. I am getting very close to building soon. I am building a legal timber pavilion, and since clay straw fill is not load bearing, they shouldn't give me a hard time when i want to start turning it into a home. Pavillion, with temporary home under it, build one side, move in, move temp house, build second side, voilà, fox trot cottage, with the option to close in the middle. I am looking into EVERY viable option.
Jay C. White Cloud
posted 4 years ago
Chad wrote: My second question is, what is your opinion on light straw clay fill, with wooden siding?
Of all the "rebirths" of old systems, this indeed has one of the highest promise in my view. A cross between a high r value insulation and a "mass wall material" like clay, we get the best of both worlds. This is the exact same concept and rendition as we have in "hempcrete," accept there we use hemp as the lofting fiber matrix and lime as the binding agent instead of a clay soil. Both are not new concepts in the slightest and have been around for thousands of years...That fact is what fascinates me in the psychological side of those that build and the ensuing hubris so many cling to, that they have "invented" something unique where most at best have rediscovered or retools a modality. I take little credit (if any?) for what I do, other than perhaps interrupt proper application of method to challenge better than perhaps many of my contemporaries seem to. The "work" I do is but a reflection of what has already been perfected over the millennia and I simple reflect a current application.
I believe (and this is more than just faith) that you will be well served by this most vernacular of methods. I also am not only intrigued by your "pavilion" approach to starting a build but can share that this reflect an innate brilliance that few may actually see and understand...Truly impressive of you to do so...
I care not to (won't) design without a "rainscreen" wall system working in concert with a "cold roof." A cold roof is nothing more than a well designed and effective "double roof" system of encapsulating a structure...or in your case...starting with a pavilion. Which, by the way, is also a brilliant way to get a structure onto a piece of property without attracting much attention. Start with a pavilion, turn that into a barn or shed (or a part thereof) and then create the living space one desire within. Simple logical progression, not unlike what has taken place in countless agrarian societies around the globe over the millenia.
Have you started a thread post yet to chronicle this project? I wish you would, and know I am here should you find I can be of service in some way. The entire approach is more than intriguing and of note for others to follow and learn from...
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