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Placing strawbales over open cinderblocks...

 
Tom Connolly
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This may be a bad idea...I am trying to test my meager knowledge of s'bale construction...the critical idea that I hear repeatedly about strawbale is the need to allow them to get rid of excess moisture. The recommended method to help facilitate this is to plaster the bales with a natural coating of some sort. Would it be helpful also to make the foundation perimeter out of cinderblocks and place the bales directly over the blocks without filling the blocks, as is usually done, leaving the holes open so that water can drain into them? The bales would have to be sealed to the blocks, of course to keep rain, etc out. I am sure there are natural options beside cinderblocks - but I don't know the proper name for bricks that have big holes in them.
 
R Scott
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Location: Kansas Zone 6a
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What is on the bottom side of the holes? Sounds like a way to collect moisture more than drain it.
 
Robert Alcock
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Location: Cantabria, N Spain
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Don't know who told you this, but it sounds like nonsense to me. Straw bales draining excess moisture? They suck the stuff up like a sponge. If you do use a cement block foundation, it will need a good vapour barrier otherwise any moisture in the foundation will suck straight up into the bales. And you don't want that to happen. I speak from bitter experience.
 
Terry Ruth
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Here is what American bale code has to say, what your trying to accomplish is not letting winter dew temps accumulate at the interface of the concrete/bales, an moisture barrier alone does not provide, an insulation does. An air vent(set bales on wood or framework) to a crawl space can replace the barrier since air flow evaporates dew, or any means of passing the vapor pressure though a material that will dry it or evaporate it. Breathable walls do this with no class 1 "barrier" Straw vertically on foundations behaves different than horizontally in walls that see water from wind driven rains that carry moisture in air. The tubes allow for moisture evaporation from a capillary action and brake from pressure and temperature differentials or gravity. That moisture vapor needs a place to go, vent, down a cinder block hole will due.....but again, dew can accumulate at the concrete/bales interfaces where a thermal bridge can also occur that is why an insulation is required per code....rock is aerated and insulates, or a limecrete.....The way I see it the cinder hole would extend the straw hole for capillary action and evaporation, an aerated insulation infill the hole would provide insulation and moisture management except where the bales contact concrete. That is aside from water proofing, there the proper drainage to keep water away needs to in place. The only other issue with the idea is structural, the blocks would need to take the loads. Limecrete has a compression rating of around 60-100 psi, rigid foam 25, so limecrete is much better under a foundation or between the cinder blocks and bales. Also, foam can not handle the deflection of creep that limecretes can.

AR105.6.5 Separation of bales and concrete. A sheet or liquid-applied Class II vapor retarder shall be
installed between bales and supporting concrete or masonry. The bales shall be separated from the
vapor retarder by not less than 3/4 inch (19 mm), and that space shall be filled with an insulating material
such as wood or rigid insulation, or a material that allows vapor dispersion such as gravel, or other
approved insulating or vapor dispersion material. Sill plates shall be installed at this interface in
accordance with Section AR105.3. Where bales abut a concrete or masonry wall that retains earth, a
Class II vapor retarder shall be provided between such wall and the bales.

AR105.6.6 Separation of bales and earth. Bales shall be separated from earth by not less than of 8”
(203 mm).

This Science can get complex, so some people follow code and put down plastic barriers and foam since they think think it protects the foundations, when in fact it brakes down chemically and from critters, under compression, creep, and deflection. Aerated blocks and other natural means do the same thing only better.
 
Jay C. White Cloud
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Hmmmm...."bad idea"...I think...means and materials on this idea on this is probably a pretty bad idea...

However...your thinking of methodolgy is very good and quite keen! I like that...

What you are thinking of (correct me please if I am wrong) is something along the lines of Thermal Core Clay Block which has been around for some time and has some very viable commercial prospects while still having a lower carbon footprint compared to other modalities.

For the "owner builder" I believe there are probably better or easier options to facilitate.

I am trying to get around to writing about all these over the next few months...

Regards,

j
 
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