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re: insulating properties on stone?
25 jun 2004
richard j kinch   wrote:

>rob green writes:
>> does anyone know the r factor (insulation rating) for a stone house? my 
>> house is the older type construction where the outer walls are stone and 
>> about 2.5 feet thick. on the inside of the outer stone walls, the walls 
>> are plastered. the outside of the house is pointed...
>marks handbook gives an r value for stone as a 0.08 per inch of thickness.  
>to consider how dismal this is, recognize that still air is 0.68, and even 
>a 15 mph wind is 0.17.  fiberglass is 4, and styrene foam 5.

the total would be 0.17 for the outdoor air film plus 0.08x12x2.5 = 2.4 for
the stone plus 0.68 for the indoor air film, ie r3.25, less than an inch of
fiberglass. you might improve it by foaming and stuccoing the outside or
foam-gluing studs to the outside and adding fiberglass and cedar shakes. 

people sometimes claim massy walls have a higher "dynamic r-value," but
that seems largely bogus to me, since they only save energy compared to
a less-massy house at times in the year when nights are cold enough to
require heating and days are warm enough to require ac.

stone houses can store coolth with night ventilation, vs keeping the
house buttoned up for 24 hours per day. they can also store heat with
day ventilation, if one is careful to avoid condensation on inside walls. 


on a day with average exterior temp t, a 68 f concrete house with 2" r10
styrofoam walls will lose or gain about |68-t|/r10 btu/h. with min and max
temps tmin and tmax, a frame house in the same location with walls with
an equivalent r-value might lose (68-tmin)/r all night and gain (tmax-68)/r
all day, with an equivalent r-value of 5(tmax-tmin)/|68-t|.

here is a list of us locations and equivalent r-values, based on nrel data:

location          month       tmin   t       tmax    equivalent r-value

philadelphia      june        61.8   71.8    81.7    26.2  [vs r10]
phoenix, az       april       55.3   69.9    84.5    76.8
flagstaff         july        50.5   66.3    81.9    92.3
prescott          june        49.9   67.2    84.5    216.3
albuquerque       september   55.2   68.6    81.9    222.5
san diego         october     60.9   67.7    74.6    228.3
houston           april       58.1   68.3    78.4    338.3
ely, nv           july        48.0   67.5    87.0    390.0
colorado springs  august      55.2   68.3    81.3    435.0
las vegas         october     54.3   68.3    82.1    463.3
elkins, wv        august      56.2   67.8    79.3    577.5
bakersfield       october     54.8   67.8    80.7    647.5
rock springs, wy  july        52.8   68.0    83.1    infinite!

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