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re: rammed earth up north
20 mar 1998
emilis prelgauskas wrote:
>stabilised rammed earth walls have both thermal mass...
sure. on the order of 10-20 btu/f per cubic foot.
>and act as if insulation because the air inclusions and thickness
>of the wall structure delay the rate of heat transfer through the wall.
sure, they delay heat transfer (vs delaying the rate of heat transfer?),
but they don't reduce heat transfer much, compared to straw, or man-made
insulation. the quantity of heat energy that moves over a certain time,
ie the rate of heat transfer, matters more than the delay, ie when the
heat flows. would you put a high value on a house that needs 2 cords of
wood heat to stay warm on the day after a cold day, vs a house that
needs 2 cords of wood to stay warm on the cold day itself?
figure 6 on page 22.13 of the 1993 ashrae handbook of fundamentals shows
soil thermal resistivities which vary from about us 0.63 to 4 per foot
of thickness, ie it would take a foot of the very best, driest soil or
6 feet or poor, damp soil to equal the thermal resistance of a mere inch
of foamboard. on the other hand, john hait writes that underground houses
surrounded by 20 feet of dry soil can be comfortable all year with some
solar glazing and earth tubes, when the soil's delay is about 6 months.
nick
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