THERMAL-BEHAVIOR OF POLYURETHANE FOAM INSULATION

Polyurethane foam insulation (PUFI) sprayed on galvanized steel was subjected for 375 days to thermally induced vapour pressure gradients. The 'warm' side of the PUFI was exposed to a temperature of 25-degrees-C and 90% relative humidity, while the 'cold' steel side temperature was cycled from -8-degrees-C to 5-degrees-C every 6 hours to simulate freeze/thaw conditions. After 375 days of testing (800 kPa.d of vapour pressure days), the PUFI had absorbed 2.7% water by volume, increasing its overall thermal conductivity from about 24 mW.m-1.degrees-C-1 to 32 mW.m-1.degrees-C-1.This means a loss in thermal resistance of about 25%. An asphaltic type vapour barrier was very effective in preventing moisture migration into the PUFI and the embedded wood framing members. Alternative construction techniques require further investigation.