Energy efficiency
Sustainability
Insulation is measured by R-value, the resistance to heat flow. The R-value of wood is 0.2 per inch, brick is 0.05 per inch – the higher the R-value the better the insulation.
Research done in Arizona found both wheat and rice straw to have a R-value of 0.5 per inch across the grain, giving strawbales a R-value from R6 to R9, almost 10 times the insulation factor of a double-brick cavity wall.
Strawbale walls therefore allow a house to be highly efficient in heating and cooling. Strawbale walls:
• dramatically increase the efficiency of a solar-passive construction, and can reduce the need for any heating and cooling equipment
• because of their increased insulation, allow installation of heating or cooling systems smaller than those in conventional homes
• provide substantial savings in gas, electricity and wood-fuel bills
• are 30 times less energy-intensive than wood-frame walls to manufacture.
Values per inch. The R-values are measured in imperial measures, the numbers in parentheses are their SI equivalents.
| Material |
Value per inch (Min) |
Value per inch (Max) |
|
| Air with no external wind |
R-1 (0.18) or less (with convective currents) |
R-5 (0.88) (Still) |
|
| Wood chips and other loose-fill wood products |
R-1 (0.18) |
|
|
| Snow |
R-1 (0.18) |
|
|
| Wood panels, such as sheathing |
R-2.5 (0.44) |
|
|
| Vermiculite loose-fill |
R-2.13 (0.38) |
R-2.4 (0.42) |
|
| Perlite loose-fill |
R-2.7 (0.48) |
|
|
| Rock and slag wool loose-fill |
R-2.5 (0.44) |
R-3.7 (0.65) |
|
| Rock and slag wool batts |
R-3 (0.52) |
R-3.85 (0.68) |
|
| Fiberglass loose-fill |
R-2.5 (0.44) |
R-3.7 (0.65) |
|
| Fiberglass rigid panel |
R-2.5 (0.44) |
|
|
| Fiberglass batts |
R-3.1 (0.55) |
R-4.3 (0.76) |
|
| High-density fiberglass batts |
R-3.6 (0.63) |
R-5 (0.88) |
|
| Cementitious foam |
R-2 (0.35) |
R-3.9 (0.69) |
|
| Cellulose insulationl |
R-3 (0.52) |
R-3.8 (0.67) |
|
| Cellulose wet-spray |
R-3 (0.52) |
R-3.8 (0.67) |
|
| Icynene spray |
R-3.6 (0.63) |
|
|
| Cotton batts (Blue Jean Insulation) |
R-3.7 (0.65) |
|
|
| Icynene loose-fill (pour fill) |
R-4 (0.70) |
|
|
| Urea-formaldehyde foam |
R-4 (0.70) |
R-4.6 (0.81) |
|
| Urea-formaldehyde panels |
R-5 (0.88) |
R-6 (1.06) |
|
| Polyethylene foam |
R-3 (0.52) |
|
|
| Phenolic spray foam |
R-4.8 (0.85) |
R-7 (1.23) |
|
| Phenolic rigid panel |
R-4 (0.70) |
R-5 (0.88) |
|
| Molded expanded polystyrene (EPS) |
R-3.7 (0.65) (low-density) |
R-4 (0.70) (high-density) |
|
| Extruded expanded polystyrene (XPS) |
R-3.6 (0.63) to R-4.7 (0.82) (for low-density) |
R-5 (0.88) to R-5.4 (0.95) (for high-density) |
|
| Open-cell polyurethane spray foam |
R-3.6 (0.63) |
|
|
| Closed-cell polyurethane spray foam |
R-5.5 (0.97) |
R-6.5 (1.14) |
|
| Polyurethane rigid panel (Pentane expanded ) |
R-6.8 (1.20) initial |
R-5.5 (0.97) aged (5-10 years) |
|
| Polyurethane rigid panel (CFC/HCFC expanded) |
R-7 (1.23) to R-8 (1.41) initial |
R-6.25 (1.10) aged (5-10 years) |
|
| Polyisocyanurate spray foam |
R-4.3 (0.76) |
R-8.3 (1.46) |
|
| Foil-faced polyisocyanurate rigid panel (Pentane expanded ) |
R-6.8 (1.20) initial |
R-5.5 (0.97) aged (5-10 years) |
|
| Silica aerogel |
R-10 (1.76) |
|
|
| Vacuum insulated panel |
as high as R-30 (5.28) |
|
|
| Cardboard |
R-3 (0.52) |
R-4 (0.70) |
|
| Thinsulate clothing insulation |
R-5.75 (1.01) |
|
|
Values for a specified unit (not per inch)
| Material |
Value not per inch (Min) |
Value not per inch (Max) |
|
| Reflective insulation |
R-2 |
R-17 (highly dependant on method of installation) |
|
| Single pane glass window |
R-1 (0.18) |
|
|
| Double pane glass window |
R-2 (0.35) |
|
|
| Double pane glass window with low emissivity coating |
R-3 (0.52) |
|
|
| Triple pane glass window |
R-3 (0.52) |
|
|
