Laid flat, a bale has an area of 0.575 m * 1.1 m = 0.58 m^2
This bale has a volume of 0.575 m * 0.4 m * 1.1 m = 0.23 m^3
To cover the floor pad of 10 m * 10 m = 100 m^2 / 0.58 m^2 = 173 bales
The perimeter is 2 * ( 10 m + 10 m ) = 40 m
The perimeter minus 4 times the bale width = 40 m - 4 * 0.575 m = 37.7 m
Which means 37.7 m / 1.1 m = 34.6 about 35 bales per layer
To make the walls 2.4 m high, 2.4 m / 0.4 m = 6 bales high
So 35 bales * 6 = 210 bales for the walls
Total = 210 bales + 173 bales = 383 bales
At city prices, 383 bales * $ 3.50 / bale = $ 1340.5

A typical styrofoam sheet of 8' X 4' X 2'' ( 2.4 m * 1.2 m * 0.05 m ) is about $ 10
Laid flat, a sheet has an area of 2.4 m * 1.2 m = 2.88 m^2
This sheet has a volume of 2.4 m * 1.2 m * 0.05 m = 0.144 m^3
To cover the roof of 10 m * 10 m = 100 m^2 / 2.88 m ^ 2 ~ 35 sheets
To make the roof 0.4 m high, 0.4 m / 0.05 m = 8 sheets high
To fill the roof, 35 sheets * 8 = 280 sheets
To make the roof stiffer, the top sheet should be extruded polystyrene, the
blue or pink colored heavier styrofoam which costs about $ 20 / sheet of the
same size as the white styrofoam sheets.
At typical prices, 245 sheets * $ 10 sheet + 35 * $ 20 / sheet = $ 3150
1 sheet of styrofoam at the bottom of the straw bale foundation would
be useful to keep the bales dry in case water leaks in through the tarps and a
thin layer of extruded styrofoam would be useful on top to provide a soft floor
surface. Thin extruded styrofoam of 0.012 m thickness costs about 1 / 4 as
much as 0.05 m thick styrofoam, so about $ 5 a sheet.
At typical prices, 35 sheets * $ 10 / sheet + 35 * 5 $ / sheet = $ 525
The total styrofoam cost is $ 3150 + $ 525 = $ 3675

Heavy duty UV resistant tarp material goes for about 1 $ / m^2. To cover
both sides of the a surface and to provide for overlap, tarp material with 3
times the surface area is needed. The floor and ceiling both have an area of
10 m * 10 m = 100 m^2, their total area is 100 m^2 for the floor plus 100 m^2
for the ceiling = 200 m^2.
This multiplied by the coverage factor of 3 is 600 m^2.
The walls have a perimeter of 40 m and a height of 2.4 m for a surface area of
96 m^2.
This multiplied by the coverage factor of 3 is 288 m^2.
The total material needed is 888 m^2, which should cost around $ 888

About $ 1000 of adhesives and sealant are needed to bond the plastic to
styrofoam on the roof and seal the gaps between the floors and walls and
ceiling.

The total cost for the shell of a square straw bale bungalow is:
$ 1340.5 + $ 3675 + $ 888 + $ 1000 = $ 6903.5
the inside surface area is ( 10 m - 0.575 m * 2 )^2 = 8.85^2 = 78.3 m^2
the cost per square meter of living space for the shell is about $88 / m^2

Assuming a comparable cost for the interior, a complete square straw bale house
would cost about 2 * $ 6903.5 = $ 13,807
the inside surface area is ( 10 m - 0.575 m * 2 )^2 = 8.85^2 = 78.3 m^2
the cost per square meter of living space for the house is about $176 / m^2

Straw bales have an average thermal resistance of 16 m * K / W and
styrofoam has an average thermal resistance of 28 m * K / W. The wall bales
are 0.575 m thick, so their thermal conductivity is:
1.0 / 0.575 m / 16 / m / K * W = 0.11 W / m^2 / K
Walls 2.4 m high have a thermal conductivity of:
2.4 m * 0.11 W / m^2 / K = 0.26 W / m / K
With a middle perimeter of 37.7 m, the wall's thermal conductivity is:
0.26 W / m / K * 37.7 m = 9.8 W / K
Windows and doors have a thermal conductivity of about 1.2 W / m^2 / K;
which is higher than the conductivity of the walls by:
( 1.2 - 0.11 ) W / m^2 / K = 1.09 W / m^2 / K
With around 10 m^2 of windows and doors, the extra thermal conductivity is:
1.09 W / m^2 / K * 10 m^2 = 10.9 W / K
So the total wall thermal conductivity is:
( 9.8 + 10.9 ) W / K = 20.7 W / K

The styrofoam roof with a height of 0.4 m has a thermal conductivity of:
1.0 / 0.4 m / 28 / m / K * W = 0.089 W / m^2 / K
With a middle of wall surface area of ( 10 m - 0.575 m )^2 = 9.425^2 = 88.8 m^2,
the roof's thermal conductivity is:
0.089 W / m^2 / K * 88.8 m^2 = 7.9 W / K

The thermal resistance of the floor per unit area is:
thermal resistance of 0.4 m of straw:
0.4 m * 16 m * K / W = 6.4 m^2 * K / W
plus the thermal resistance of 0.062 m of styrofoam:
0.062 m * 28 m * K / W = 1.74 m^2 * K / W
for a total thermal resistance of 8.3 m^2 * K / W
or a total thermal conductivity of 0.12 W / m^2 / K
The ground underneath the floor decreases the thermal conductivity there by around a factor of two, so the approximate total conductivity is:
0.12 W / m^2 / K / 2 = 0.06 W / m^2 / K
With a middle of wall surface area of ( 10 m - 0.575 m )^2 = 9.425^2 = 88.8 m^2,
the thermal conductivity of the floor is:
0.06 W / m^2 / K * 88.8 m^2 = 5.3 W / K

The total thermal conductivity of the round straw house due to conduction is:
( 20.7 + 7.9 + 5.3 ) W / K = 33.9 W / K
in houses, the heat loss due to air movement is roughly the same as the conduction losses, so the total thermal conductivity is:
2 * 33.9 W / K = 67.8 W / K ~ 68 W / K
 
 

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