Cob R of dirt (was Cordwood Homes)

[M J Epko]

At 09:03 PM 12/1/97 -0600, you wrote:
>I was looking at a website for earth-sheltered (underground) homes and I
>think it was there that I saw a statement that said one foot of earth on
>your roof would reduce your internal temperature swing to only 40
>degrees or so, when the outside temp swing was much higher (80 or
>100-can't remember).  Meaning that if it went from 0 to 100 degrees
>outside, the fluctuation in your house would only be 40 degrees (or so).

	Over what period of time? A lot of this is climate-dependant. If the
outside temperature is 0F for a month, the ground will freeze well past
that depth; the heat loss would be significant. Up here, seasonal
temperature fluctuations register in the soil to a depth in excess of 25
feet. However, wide daily fluctuations are erased at about a foot - so the
premise is correct on a daily basis.

	From the book Earth Sheltered Housing Design (which was written using
Minnesota's climate data) is a test where a heating-season comparison was
made between two earth-sheltered roofs: the first had 9.8 feet of dirt over
precast concrete, and the second had 18 inches of dirt over 3.9 inches of
polystyrene on top of precast concrete. The almost-ten-feet of dirt yielded
a 2.4% reduction of heat loss over the other one for the season. Not very
much. It says "... in order to compete effectively with standard insulating
materials, soil depths in excess of 2.75m (9 ft) would be required on the
roof... the increased depth of the building would also reduce heat losses
through the walls and floor."

	In more temperate climates with high diurnal temperature swings, the
thermal mass qualities of earthen structures have greater effect. (R values
don't address thermal mass effects, which can be significant in the right
setting.)



   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      M J Epko        duckchow at ix.netcom.com
      almost Wyoming, north of Nebraska, USA
               by way of New Mexico
      (not soon enough) - for now, Minnesota
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

     The heart of a fool is in his mouth, but 
     the mouth of a wise man is in his heart.
                          - Benjamin Franklin