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Earth berm insulation

 
Justin Wolfe
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Originally, I wanted to build an earth bermed roundhouse like the be on simondale.net. Problem is, I have been told by several starwbale builders that it is not a good idea to use straw insulation below grade. What natural material can I use to insulate elbow grade?
 
Brian Knight
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Location: Asheville NC
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Check out Mineral Wool and Foam Glass. The more continuous the better. Double layers and over lapping seems boosts performance of all exterior insulative sheathing.
 
Justin Wolfe
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Thanks much! The foam glass looks pretty promising! What I looked into about the mineral wool says it's prone to bacteria when wet.
 
Brian Knight
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Do you mind passing along the source for that tidbit about bacteria? Mineral wool doesnt really contain any mold or bacteria food but I could see how bacteria might find it a comfortable place to hang out. Even so, what harm is it doing if its outside the building envelope? Currently, mineral wool can be cost competitive with foam (still my preference) but foamglass is typically 2x more expensive.
 
Justin Wolfe
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I just read it on Wikipedia (I know, forgive my source sins!)

Anyways, the whole bacteria thing could matter, I mean, I would imagine it could lead to odor or contaminated soil around the house.

I actually changed my plans to be a bit simpler. The new plan is half bermed on the south side tapering toward the north entrance. Do the bermed portion with earthship tires and insulate above grade with strawbale. This will be more conducive to lighting the home and it will make my potential water problems go away.

However, either of these materials (pending the whole bacteria question) may still work well to insulate the earth roof, so I won't waste the info!
 
Justin Wolfe
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http://en.wikipedia.org/wiki/Mineral_wool

Link for you btw.
 
Brian Knight
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Location: Asheville NC
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Thanks. Couldnt find the mold/bacteria reference though. Did see a picture where they used it inappropriately in the missing fireblock picture. Mineral wool is not an air barrier. Air barriers are largely more important than insulation for most climates.
 
Justin Wolfe
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Yeah, I'm planing on using this stuff below grade. Above grade I will use clay plastered straw bales set into round wood framing. Think of it as an improved hobbit house.
 
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