Another 'moisture' question about Strawbale houses

Discussion in 'Shop Talk' started by moonwolf, Aug 22, 2005.

  1. moonwolf

    moonwolf Well-Known Member

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    I have read about stucco as the exterior for straw bale houses in a humid climate can raise the moisture level within the straw to a level that might cause rot.
    So, the question is that assuming you do your best in all aspects of a straw bale house with good roofing and avoid leakage by having extended overhangs, a proper foundation, etc. Now if it's humid and the stucco absorbs moisture, it apparently will wick down to the straw where it will not be able to escape. Moisture levels are supposed to be about 15 to 20% at the most. Higher than that for any period of time, the straw rots and the walls can fail. Am I correct with this deduction?
    Does anyone live in a strawbale house in a moist or humid climate? In the upper midwest, The summers, spring, fall can be very humid with days of wet with rain that obviously can touch the stucco exterior of a house.
     
  2. WisJim

    WisJim Well-Known Member Supporter

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    It is humid in summer around here (western Wisconsin). I haven't heard of the problems that you mention--the straw isn't subject to any worse moisture than it would be stacked in a haymow of a barn, or so it seems to me. Many houses put in a small "witness" window or panel in a wall, so that you can open it and actually see the straw, which I suppose would give a chance to discover any potential problems when they occur. And, of course, the roof overhang should prevent much rain from striking the outside stucco walls, and they would dry quickly if they did get damp.

    The fellow that my son works with has been researching alternative building methods for quite a few years, and has checked out many older straw bale structures, and has found the only serious problems can be traced to poor design, especially straw bale walls too close to the grade, or designed with details that allow water to regularly penetrate the wall.
     

  3. moonwolf

    moonwolf Well-Known Member

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    thanks for your response, Jim.

    That is also one thing of concern about the straw not being in contact at ground level. I was reading some material from CMHC (Canada Mortgage and Housing Corporation) and they mentioned the idea about stucco staying moist and a concern that it could build moisture down to the straw underneath. They gave some figures above 20% moisture content and said at this level the straw could irreversible be on a path for rotting. I can see the analogy of straw stored in a barn, except that it isn't in contact with a coating of stucco that has absorbed humidity or rain??

    A moisture meter would probably give a good indication to monitor levels, but if it isn't drying from a high moisture level, then what? I guess maybe I worry too much about this. I've heard more positives than negatives about strawbale construction done right. I know of one house stuccoed that was completed in 2003 near Thunder Bay which would be a similar seasonal moisture and climate. I should try and ask them about their moisture content, or if it's a concern.
     
  4. agmantoo

    agmantoo agmantoo Supporter

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    Moonwolf, I live in the sunny southeast, read that to be the hot and humid! We have a lot of rain additionally in a good non drought year. The only stucco that you see here is high in the eves of some older homes or over the foam used in newer homes. The stucco will actually crack over time and it does create a problem in this area and becomes high maintenance. Usually with the blowing winter rains the stucco gets saturated and then we have some cold and the surface will freeze. Stucco is fine in some areas but this is not one of them. Additionally stucco will mold here. If I did not see a number of homes built years ago around the area I would not choose stucco unless I could give it some type of waterproofing. The people from years passed knew what would survive a particular area, stick with their findings.
     
  5. moonwolf

    moonwolf Well-Known Member

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    agmantoo,
    there are a lot of stucco exterior finished houses here. My neighbor across the road has a stick framed house with stucco siding. No problems with moisture, but the difference is that the conventional framed house has a vapor barrier tyvek outside covering over the side sheating before the stucco is put on. No 'wicking' could occur down to the wood frame as I am speculating that could possible happen in a straw house. You can't put a layer of vapor barrier either, because the straw has to 'breathe' through the outer or inner layer which is the stucco. So, that brings us back to the concern about a moisture level that might occur in strawbale houses. Sure, you could monitor the levels or look through a peep window to see the staw looks dry, but if it's over 20% like the reading suggests the straw could begin rotting? then what? Sounds like nit picking, I know. :shrug:
     
  6. Ross

    Ross Moderator Staff Member Supporter

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    My brothers house is a frame stuco covered house and there is no rot behind the walls we've ever found. The house is from the 1920's. I'm wonderign if you could not have the straw baled with a preservative sprayed on, either a biological inoculant or a simple acid type (not chemical) that would halt spoilage from any slight increases in moisture. As well I'd guess the load bearing design for straw bale buildings might increase the chances of spoilage over the post and beam design as the straw is preloaded (IE more compressed) and can't breathe as well as the other bales. Still if stuco is letting moisture in it's also letting it out. I'd think so long as your location allows for some sun exposure and a little breeze it's going to dry faster than it will rot!
     
  7. snoozy

    snoozy Well-Known Member Supporter

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    Moonwolf -- you worry too much! My strawbale house is in a soggy county in the Pacific NW, as I have mentioned before. We have heavy moss on the trees year round. Algae grows on our cars. We are famous for rain. Think Vancouver Island. (Vancouver is full of stuccoed houses, BTW.)

    I just tested the north wall's moisture meter probe which is imbedded at 6 inches above the floor. It reads 11.5%. That wall has never seen sunlight, and it has been 7 years. I have never seen it read higher than 14%, in mid winter. The other walls would read about 8% in Aug (the probes are behind furniture and I am too lazy to move them.) For the moisture to get to 20%, I think you might have to have a pipe burst or a prolonged roof leak. You'd have to have actual water on the bales. And it still would not be a problem if you were able to dry it quickly. These bales are very tightly packed. It's hard to get a needle through them.

    How did the place feel? And I will ask one more time: How big is this house and how much are they asking? I'm just curious.
     
  8. moonwolf

    moonwolf Well-Known Member

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    I think that's the key, is the stucco breathes enough to let moisture wick 'out' faster than any of the straw would absorb moisture. I would hope that's the idea anyway. I read one guy that used the lime based earth plaster and said it 'breathed' more than stucco, so that would be the better way to go I should think. Having stucco on there already is the problem, and one hopes the breathing out of moisture will work over the long haul.

    As for sparying preservatives, that might work for a short time, but do you really think it will last? Also, what effect might any chemical have on contact with straw for a long time? The chemical itself might break down the straw. I think so many things about the strawbale house is untested.
    The house is post and beam construction, so the straw isn't load bearing. I suppose if worse came to worse down the road, one could rip out the straw walls and frame it among the post/beam load or redo a straw wall at a time. A work in progress....
     
  9. Ross

    Ross Moderator Staff Member Supporter

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    That's the point a non-chemical preservative either bacterial which I really don't know how long it lasts but if there's moisture it acidifies the straw to kill mold, or a straight acid very much like vinegar sprayed on and again you're simply acidifying the the straw to prevent mold. No methyl ethyl death chemicals.