2025 Important Cautionary Update
Immediately after moving into the house 2 1/2 years ago, we began seeing a tiny insect, particularly around the windows, only to realize that they were rice weevils. The detailed discussion of the weevil problem renders this post academic.
* * * * * * * * * * * * * *
The Choices
As our design evolved, I waffled as much on the insulation as on French drains, the extent and composition of the earth contact walls or the design of the foundation walls. Hands down, spray foam would be the best choice for several reasons and worst choice for several other reasons. Its positives are a high R value (at 6.5 per inch, it is twice that of most other insulations), it blocks air infiltration and it adds strength and rigidity to the wall or ceiling. Its negatives are that it mostly comes from petroleum (as I understand it, the addition of soy is more greenwashing than creditable), has high embodied energy, out-gases VOC's for a while after application and it is incredibly expensive especially since it is not DIY-friendly and our design for a super-insulated house calls for exterior walls and cathedral ceilings that are extraordinarily thick.
So what else? My second choice was cellulose for both the walls and the ceilings. The advantages of cellulose are that it is made from recycled paper, which is about as green as it gets, it does a pretty good job of sealing off air infiltration, particularly in walls as thick as ours will be, it can be sprayed into walls before drywalling much like spray foam and it is relatively inexpensive. There is one important disadvantage of cellulose for our cathedral ceilings -- for a decent R value, it has to be dense-packed which requires the space between the ceiling and sheathing to be entirely enclosed so as to be able to pack the insulation densely. With our mini-attic (cathedral ceilings) design, the space that exists under the sheathing precludes dense-packing. The same goes for loose fiberglass which would also have to be dense-packed to function well in a cathedral ceiling. Fiberglass batts, in my opinion, are not an option for super-insulation. However, we may use them for the 6" exterior walls of the garage (but not the wall between the garage and the house that will match the other exterior walls).
Rice Hull Insulation
Since none of the conventional insulations suited our needs perfectly and still needing to reduce costs, I went searching for alternatives. I had reread Don Stephens' article on Annualized GeoSolar dozens of times but blew off his argument for rice hull insulation as impractical for us. About a year ago, when searching for alternative forms of insulation, I finally Googled rice hulls. Up pops The Rice Hull House, a slide show on truss walls and rice hull insulation emanating from Washington, LA. Also I found an article written by Paul Olivier on the attributes and physical properties of rice hulls. (I suspect that Paul was the one posting the slide show as well.)
Price Quotes
After getting a price quote on hulls from a southeast Missouri rice mill that was
considerably higher than the price Paul mentioned in his article, I exchanged emails with him seeking input. He advised looking further, that they should be available at $15 per ton. A freight quote for a grain trailer-load (18 tons) from Arkansas or Louisiana was $500-900. Eighteen tons at $15 per ton plus freight would run $770 to 1,170 for as much as my rough calculation suggested we would need to do our entire house. If not, depending on the amount we were short, we would either finish up with cellulose or order another trailer-load.
A quote for doing the whole house with cellulose was $4,700. God only knows what it would be for spray foam. And the quotes would be higher now because our design has recently morphed into walls and ceilings that are several inches thicker.
Properties of Rice Hulls
As explained in the article by Olivier, rice hulls possess a high silicon content which makes them essentially inert when it comes to combustibility, mold growth, vermin and insect support -- even more so than for cellulose. The thermal resistance (R) factor for rice hulls when poured or blown into a wall or ceiling cavity is R-3 per inch, which is similar to loose fiberglass and cellulose. Interestingly, Paul also said diatomaceous earth can be added to the hulls as a further measure against termites. The earth particles find their way under the insects' shells and abrade them to death.
Price Quotes
After getting a price quote on hulls from a southeast Missouri rice mill that was
A quote for doing the whole house with cellulose was $4,700. God only knows what it would be for spray foam. And the quotes would be higher now because our design has recently morphed into walls and ceilings that are several inches thicker.
Properties of Rice Hulls
As explained in the article by Olivier, rice hulls possess a high silicon content which makes them essentially inert when it comes to combustibility, mold growth, vermin and insect support -- even more so than for cellulose. The thermal resistance (R) factor for rice hulls when poured or blown into a wall or ceiling cavity is R-3 per inch, which is similar to loose fiberglass and cellulose. Interestingly, Paul also said diatomaceous earth can be added to the hulls as a further measure against termites. The earth particles find their way under the insects' shells and abrade them to death.
