According to the Solar Energy Industries Association, properly insulated homes use half the energy of those without insulation.

Underhill House is a blend of old and new ways to insulate.

Over half the house’s walls is insulated with straw bales with an R-value of 30-45.

The expedient castor bean! So easily pressed into valuable oil.

The other half – that part below ground and the walls that are mostly filled with windows (as well as the roof) –  are being insulated with Icynene LD-R-50©spray foam made using environmentally friendly and renewable castor oil with an R value of about 30.  (The roof insulation is more like R50.)

Castor oil is a useful substance.  According to an Alternative Field Crops manual prepared by the University of Wisconsin and University of Minnesota in 1990, the Egyptians burned it in their lamps more than 4,000 years ago.  In the U.S. it has been used as a machine lubricant and has also been used in the making of soaps, nylon, varnishes and paints.

The castor bean busily sucking CO2 out of the air.

About a million tons of castor beans are grown each year world-wide with India being the top producer.  The U.S. is not even among the top ten, so I’m not sure how local our castor bean foam is. The U.S. demand for the crop peaked in the early 1950s when the government subsidized castor bean growers for a short time.

Perhaps we’ll see more fields of castor beans as its use as an insulating foam increases.


1. Castor oil insulation is very effective at reducing the levels of carbon dioxide in the atmosphere. According to Ecotec Insulation   nearly 3.5 kilograms of CO2 are prevented from entering the atmosphere for every kilogram of castor oil used to make polyol (a main component of LDR50 Insulation) because the polyol was not created from petroleum.

2. Also the castor oil crop is estimated to absorb carbon dioxide from the atmosphere at a rate of 34.6 tons per hectare (about 2.4 acres), with two growing cycles per year. According to a study by the Department of Energy, there are nearly ZERO NET GREENHOUSE EMISSIONS from the production of castor oil and polyol used for LD-R-50©.

3.  Substituting a portion of the petroleum based polyol with castor oil creates a renewable material because it can be grown on marginal lands, which are not competitive with food production lands, according to the manufacturers .

 Foam insulation also appealed to us because it fills spaces so completely,

and Underhill House has many irregular spaces to fill.

Jason and Todd of Kinsler Companies  worked for about 6 hours filling the spaces and then trimming off excess foam and cleaning up.

It’s fascinating to watch the process.  Jason set up two drums of material that fed in two separate lines into the house.  They are mixed in the nozzle just before spraying.

When the foam is sprayed onto the wall, it looks like thick paint for a moment, then it expands like liquid popcorn.

Jason said some companies fill the cavities only partly to avoid having to cut off too much excess when they trim  the foam back to the wall studs.  But his company fills them completely to make sure the entire cavity is filled.

Like so many attempts to choose the most sustainable option, it’s a trade off.

Yes, there is a bit of wasted foam in the beginning, but the more complete insulation will result in fuel savings for many years.  We are trying to build a house that will last for at least several hundred years, so it may well be worth it in the long run to overfill a bit.

Jason said that they used to grind up this scrap foam and blow it into attics, but the process became too costly to justify.  Now the excess is landfilled.  Sigh.  I helped pick up the scraps of foam and managed to reuse some of them to fill several cavities that were not sprayed such as the built out space behind the sofa in the den and a cavity where our bedroom  closet fits around a timber.  So I felt a little better about the scrap foam.

Bottom line – these thick walls filled with low-density, open-cell spray foam insulation and straw bales should really help keep us warm in winter and not too hot in summer using the least possible fuel.

How are your house insulated? 

Are you happy with your R-value? 

Are you thinking of improving it? 

What types of material do you think are good ones?

3 replies

  1. We were talking to a sheep farm yesterday regarding their wool fleeces that they have trouble getting rid of. Wool insulation seems to run at an R value of 3.5-3.8 per inch, so 8-9 inches would be needed to get an R-value of 30. I know we can get it cleaned easily enough but not sure how to get it processed from that point though. Although the material is local it will have to be sent away to be cleaned. It is rather too much work for one couple to do and a lot of waste to think about. Like you say, lots of trade offs to think about.

    • Wool is such a wonderful material! That’s a great idea, Joanna. I’ll be curious to hear how it turns out.
      A few years ago I saw some 2″ thick cork being sold on Craig’s list. I have always been sorry I didn’t get it then, but I had no where to store it. It was being recycled out of an old walk-in freezer.

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