Energy efficiency


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)