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"R" Value

The "R" Value of wood increases with a decrease in temperature

Testing done by the Eastern Forest Products Laboratory, Ottawa, shows that 6 inches of white pine wall is capable of meeting the recommended value 6"R=12, during the three coldest months of an Ottawa winter.

The average value of thermal resistivity (reciprocal of thermal conductivity) of white pine 1"R=1.25 [ft.2 hr. of/BTU in] is based on thermal conductance measurements at about 10% moisture content and 73° F mean temperature of the wood. Both ASHRAE Handbook of Fundamentals and Handbook of Chemistry and Physics report an average value of 1'' R = 1.32 for white pine under these consitions. In the E.F.P.L. test (at about 10% moisture content and 41° F mean temperature of the wood -- That is 14° F surface temperature on the cold side, 68° F on the warm side of the wood), the termal realitivities measured were scattered between the boundaries of 1''R = 1,5 and 2.1, or an average of 1 '' R = 1.8.

Complete information of these test is available in Interim Report EFPL-6-3-307, 'Thermal Resistivity of White Pine", from:
Eastern Forest Products Laboratory
Canadian Forestry Service
800 Montreal Road
Ottawa K1G 3Z5