The newest SPF roof in the NRCA/NRF study had a core density of 64.1 kg/m3 (4.0 pcf) with a compressive strength of 448 kPa (65 psi). The oldest (installed in 1975, at the time of the study this roof was about 21 years old) had a density of 56.4 kg/m3 (3.5 pcf) with a compressive strength of 685 kPa (99.3 psi).
Moisture content values
Average moisture content was negligible, at 1.02 percent by weight. Dupuis noted the physical properties of the evaluated roofs came up positive-regardless of the age of the installation-in most cases exceeding the required minimums for new installations despite in-field service of 25 years or more. (Determined by oven drying samples at 50 C [122 F].)