THERMAL-BEHAVIOR OF POLYURETHANE FOAM INSULATION

Polyurethane foam insulation (PUFI) sprayed on galvanized steel was su bjected for 375 days to thermally induced vapour pressure gradients. T he 'warm' side of the PUFI was exposed to a temperature of 25-degrees- C and 90% relative humidity, while the 'cold' steel side temperature w as cycled from -8-degrees-C to 5-degrees-C every 6 hours to simulate f reeze/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 preventin g moisture migration into the PUFI and the embedded wood framing membe rs. Alternative construction techniques require further investigation.