Conductivity (k) "the number of BTU’s per hour that flow through 1 ft2 of material that is 1" thick, when the temperature drop through that material is 1F degree."
Resistance (R) "hours needed for 1 BTU to flow through 1 ft2 of a given thickness of a solid when, again, the temperature difference is 1F degree."
Conductance (C) "the number of BTU per hour that flow through 1 ft2 of a given thickness of material when the temperature difference is 1F degree.
When Conductance (C) is referred to it is a thickness other than 1".
(R) is the reciprocal of the conductivity. (1/k)
R increases directly with the thickness. (x/k) x=thickness k=conductivity
Airspaces placed between bricks roughly triple the R-value of one brick with minimal R-value variance from thickness. Ex. [brick] [air space] [brick]
Foil lined on one of the inner sides improves the R-value for the wall construction.
Types of Stabilized Earth Blocks 3 x 6 x 12"
Soil/ fly ash (10%) mix:
- control block
- straw interwoven
- expanding foam before cured
- expanding foam cured
- rigid insulation (thick)
- shredded batt insulation (thick)
- shredded batt insulation (thin with perlite)
- vertical planes (4) of batt insulation strips
- horizontal planes (4) of batt insulation strips
Soil/ cement (25%) mix
- soil (75%)/ haydite (25%)
- soil (50%)/ haydite (50%)
- soil (25%) haydite (75%)
Block Removal from Machine
Many of the stabilized earth blocks (SEB) crumbled during the removal process from the machine. We discovered that the best way to lift the blocks is to have one person lift with their forearms pressed along the linear side while another person stabilizes the short ends. By lifting together it is possible to move the block on to a steel slab and transport it to a controlled location.
Even with the successful method of moving the blocks some insulating blocks would not hold together. When a foreign object is placed inside the mold and compressed, when the pressure is released the inner material pushes the block apart. Expanding foam cured and wet, rigid insulation, thick shredded batt insulation, and planes of insulation all failed because the inner material was too large and caused cracking once cured (see figure 1).
The blocks that did hold used materials of small surface area that would not interfere when compressed in the machine. From this information we decided that it was necessary to use small, multiple pieces of an insulating material to achieve a successful SEB. The control, interwoven straw, thin shredded batt insulation with perlite, and each haydite block were successful. Even with the presence of different insulating materials in the soil, the R-value did not greatly improve in the blocks. There is little one can do with the stabilized earth blocks alone but through the use of a construction design system a very well insulated wall can be achieved.
Building Systems
- 1.334 = R-value of block per inch
- multiply the R-value of a SEB by 3 if there is an air gap
- R-2.4 per inch with the grain of the straw bale
- R-3 per inch against the grain of the straw bale
An 18" straw bale insulated between two 6" blocks with an air gap between, will achieve an R-value of R-67.2 = [ (1.334 x 6") x 3" ] + 2.4 x 18" (see figure 2)
R-19 Batt insulation between two 6" blocks with an air gap between, will achieve an R-value of R-43 = [ (1.334 x 6") x 3" ] +19 (see figure 3)
6" of stuffed straw between two 6" blocks with an air gap between, will achieve an R-value of R-42 = [ (1.334 x 6") x 3" ] + 3 x 6" (see figure 4)
A 2" air gap between two 6" blocks with foil lined on one side of the inner wall will achieve an R-value of R-24 = [ (1.334 x 6") x 3" ] (see figure 5)
Resources
Mechanical and Electrical Equipment for Buildings / Benjamin Stein, John S. Reynolds. — 9th edition
Fig. 1
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Fig. 4
Fig. 5