Issue link: http://cp.revolio.com/i/1121626
Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values Page 6 Temperature Building insulation performance differs when tested at mean temperatures other than 75°F (24°C). This behavior is recognized in ASTM standards, by manufacturers, and by authoritative publications 2,3,9,11-13 . The mean temperature at which the thermal resistance of insulation is measured is a key factor to consider when used in buildings exposed to both cold and hot conditions, which is the prevailing case across North America. -35 -25 -15 -5 5 15 25 35 45 55 65 -31 -13 5 23 41 59 77 95 113 131 149 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 Mean Temperature (°C) Mean Temperature (°F) Conductivity (W/mk) 0.60 0.50 0.40 0.30 0.20 0.10 0.00 Conductivity (Btu-in./hr-ft 2 -F) Figure 2. Thermal Conduc vity of Building Materials as a Func on of Mean Temperature 14 OSB Framing lumber FG batt Cellulose HD EPS (Std panel) XPS (Box walls) 2 pcf ccSPF PIC (Cartridge TB) Figure 2 shows that the thermal conductivity of many building materials decreases as the mean temperature decreases 14 . R-value correlates inversely with thermal conductivity. Thus a lower thermal conductivity at colder mean temperatures means that the R-value for the material increases as the temperature decreases. One insulation, polyisocyanurate insulation, does not exhibit this typical behavior. At mean temperatures below approximately 60°F (16°C), its thermal conductivity increases significantly, and thus the R-value decreases significantly. It is important to adjust the R-value for the actual conditions when conducting a detailed analysis of the building at conditions with a mean temperature other than 75°F (24°C). This analysis may require further consideration of both winter and summer conditions. Alternatively, the lowest R-value based on summer and winter conditions of the building may be used as a conservative approach. Table 2 provides example calculations of mean temperatures based on different exterior climate conditions and an interior temperature of 72°F (22°C).