Loose straw for insulation

I was thinking of a semi-underground or bermed home, and want to hear opinions on the use of loose straw for insulation. I'm far from sure this will work, but envision it this way: Roof (e.g. plywood or equivalent), then a tarp, then 2 feet of loose straw, then epdm membrane. Could stop there, or could add a few inches of sand to protect the epdm from sun.

The point is, roofs should be relatively light weight (in my opinion) to save on structure costs. The straw will pack down over time, and more can be added later to boost it up. Probably won't take too long to be as dense as a straw bale, and easier to make it conform to curves and such. Anyway where I am thinking of building, the straw comes mostly in large (5 foot diameter) round bales; hard to use those directly, heh.

FYI I dismantled a root cellar in Wyoming (starting to cave in, in places) that had probably been there for almost a hundred years. Back then there was no plastic. The construction method was lots of timbers, lots of split rails on the ceiling, a layer of loose straw, and a foot or two of dirt. That was it! Of course that area probably gets all of 13" of rain a year, and the soil has enough clay in it to prevent water percolating down before it evaporates off the surface!

Would consider using lava pumice instead, won't compress down, and no fire or insect hazard. would be good to not make depressions for water pooling.

1/4 -3/8 cinders are about the best, and that size is too large for roadway de-icing.
check the highway dept, prob have loads of it stacked up.

there is some info out there for using earthbags filled with cinders for walls. Highest R you can get.

https://earthbagbuilding.wordpress.com/2010/10/03/using-scoria-for-earthbag-building/#comment-9445

If the farmers near you use agricultural net-wrap on their round hay bales that might work better. It's plastic, so it wont rot or degrade once it's out of the sun. Plus it is a liability to get rid of because its difficult to clean enough to serve as a recyclable plastic. Any farmer that uses it much has a pile around, or pays a lot to stuff it in a landfill.

Paul Bonneau wrote:I was thinking of a semi-underground or bermed home, and want to hear opinions on the use of loose straw for insulation. I'm far from sure this will work, but envision it this way: Roof (e.g. plywood or equivalent), then a tarp, then 2 feet of loose straw, then epdm membrane. Could stop there, or could add a few inches of sand to protect the epdm from sun.

The point is, roofs should be relatively light weight (in my opinion) to save on structure costs. The straw will pack down over time, and more can be added later to boost it up. Probably won't take too long to be as dense as a straw bale, and easier to make it conform to curves and such. Anyway where I am thinking of building, the straw comes mostly in large (5 foot diameter) round bales; hard to use those directly, heh.

FYI I dismantled a root cellar in Wyoming (starting to cave in, in places) that had probably been there for almost a hundred years. Back then there was no plastic. The construction method was lots of timbers, lots of split rails on the ceiling, a layer of loose straw, and a foot or two of dirt. That was it! Of course that area probably gets all of 13" of rain a year, and the soil has enough clay in it to prevent water percolating down before it evaporates off the surface!

Our root cellar on the farm was done the way you describe the WY cellar and many of the old spud cellars around here (S Idaho) were done the same way or similar. Some are still standing...sort of, after 80 yrs or so. The difference is that you'll be heating the inside of your home (I presume) which could create some additional moisture problems within the straw. Secondly, I don't know where you're located but 2' of straw may not provide you with the kind of R value you'd like.

Re cinders/lava, they would seem like a good idea here due to potential moisture issues. As linked previously, Kelly Hart has reported good results using them in "earthbag" construction. However, the thickness of his walls and use of papercrete plaster likely made up for the lack of R value other wise. Though I have not seen any formal testing of a completed wall insulated with this material, cinders only have an R value of .59/inch. Pumice is slightly higher at .86/inch. Again, you may not be able to get the kind of R value you'd like.