Monday, February 23, 2015

Timeline - Design Evolution - Insulation

Past three years

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 diatomateous 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.   

Tactical Issues
Since the blower used with cellulose is not robust enough for hulls, a stronger homemade blower is necessary --  as shown in the slide show mentioned above. Chances are we will make a blower but we have also been brainstorming about ways to build walls and cathedral ceilings in non-typical ways in order to use rice hulls 
Insulating a 2 x 4 wall with hulls before sheathing and raising (internet pic)
without a blower. For example, the truss walls (15" thick) could be built in 4 x 8 sections and insulated before raising them. Or the cathedral ceilings could be closed on the bottom using the  already-planned pine tongue and groove wood ceiling, the hulls poured onto the ceiling between the rafters then the roof sheathed and waterproofed -- obviously an upside down approach compared to conventional construction.

Another tactical issue is how to receive the hulls.  Probably we will elect to have
them dumped on a paved parking lot and use Lawn Funnels and lots of volunteers to fill plastic contractor bags..  The bags could then be hauled to the building site, palletized and tarped until needed. Some of the hulls will undoubtedly be poured directly into spaces to be insulated but, realistically, a home-made blower will come in handy.

(Parenthetically, the Lawn Funnel for paper bags is still available but the model for plastic bags has been discontinued.  Fortunately, we have quite a few of the plastic bag model left over from when the Young family still owned the patent for the Lawn Funnel and manufactured / distributed them.)


  1. Hi,
    Just wondering how this project went. I am considering blowing rice husks as ceiling insulation.

  2. We are still several months removed from needing insulation. My research suggests some questions for you. How far from the Mississippi delta do you live since the cost of freight will be the major issue? How thick will the insulation be since rice hulls weigh more than dense-pack or blown fiberglass or cellulose? Typical 1/2" drywall may not support the thickness necessary for the R-value (+/- 3 per inch) you might want. Have you given any thought as to the design for a blower robust enough to blow hulls and are you willing to make one yourself? Insulation blowers from rental or big-box stores apparently are too wimpy for rice hulls. In my post above, check out the link to the "Rice Hull House" for pictures of a DIY blower. Good luck and congratulations on thinking outside the box.


As a do-it-selfer-in-training, I welcome your comments.