re: building a concrete block home?!
15 nov 1996
kenneth a. davis wrote:
>i would like to know how much materials it would take to build a 40x60
>concrete block home (just blocks and roof..no interior(walls or otherwise)?
a 1-story shoebox would have 2(40+60)8 = 1600 ft^2 of walls and 2400 ft^2 of
roof, requiring 1800 blocks for the walls and 2700 for the roof, if assembled
blocks measure 8x16/144=0.88 ft^2 each, ie 4500 blocks altogether.
a quonset hut 20' tall in the middle with an 1885 ft^2 roof needs 2120 blocks
for the roof and 353 for the endwalls, 2473 altogether.
a quonset hut made with 1/2" of cement over 3 layers of 4' chicken wire over
4' burlap over 16 curved double 1x3 beams on 4' centers, each 64' long, needs
16x64x2 = 2048' of 1x3s at 10 cents/foot, ie $205 for wood, $185 for burlap,
about $600 for chicken wire and $100 for cement, ie $1090/2400 = 45 cents/ft^2,
ignoring the endwalls.
>also if anyone knows how would be the best way to insulate this type of
>home for optimum energy efficiency?
beadboard on the outside, with latex paint over that. make the 60' side run
ew, cover the lower 12' with dark window screen and a $36 piece of greenhouse
poly film or a $700 single layer of polycarbonate plastic, with a 6" air gap
underneath, and allow house air to enter the gap through some holes at the
bottom and flow through the window screen sideways. let some of the air flow
back into the house at the top while the rest flows under and heats a 20' wide
x 60' long x 2' deep (avg) pond under the ceiling, made from steel cables
supporting more chicken wire ferrocement, under a layer of epdm rubber roofing
material. the pond could also provide hot water for the house. a shallow arc
of 4' wide foil underneath would avoid overheating the house.
where i live, the minimum house wall insulation thickness is determined by
the solar house heating performance requirement in cloudy winter weather, as
well as the thermal mass of the house. with 2200 ft^2 of roof and endwalls with
average r-value r, we need about 24(68-30.4)2200/r = 2 million/r btu to stay
warm on an average january day in phila, or 10 million/r btu for 5 cloudy days
in a row. the pond has a thermal capacity of about 20x60x2x64 = 154k btu/f, so
if it's solar heated to say, 120 f, and it can keep the house at 68 f with
warm air moving down to the house with a ceiling fan and a thermostat until
the pond reaches 80 f, we can store (120-80)x154k = 6.2 million btu of useful
heat in the pond. if 6.2 million = 10 million/r, r = 1.6. a half-inch of r4
beadboard should be enough wall insulation for cloudy day-performance.
on an average january day in phila, this house would collect 662k btu of heat,
while losing about 6(68-38) = 130 btu/ft^2 through 720 ft^2 of r1 glazing,
for a net gain of 536k btu. with r1.6 insulation, the house needs 2m/1.6
= 1.25 million btu/day, so average day performance requires a higher level of
wall insulation, eg r5. or a 72' long commercial plastic film greenhouse on
one end, or a glazed 60' long x 12' high strawbale wall. a reflecting pond
along the south wall would increase insolation by about 30%, raising net gain
to 730k btu/day, and lowering the required r-value to 2 million/730k = 2.8.
one alternative might be to use lightweight insulating concrete, eg 30 pcf
roof slab concrete with an r-value of 1 per inch, made with expanded shale,
according to bill sypher of norlite, inc. (508) 263-0170 and dr. john ries,
p.e. of the expanded shale, clay and slate institute (801) 272-7070.