is used to calculate the in situ r value of the fiberglass batt in each of the four tests the nominal r value for the batt insulation is 19 the last column in table 4 is a ratio of the in situ r to the nominal r expressed as a percentage the primary measurements from the lscs tests are the steady state heat flow through a 64 ft 2 test specimen and the temperature difference across the test specimen equation 1 is used to calculate the r value from the measured values the measured heat flow and heat flux is an average value over the area of the test specimen the measured heat flux therefore includes the heat flow through the purlins as well as the heat flow through the insulated region between the purlins the exterior air film resistances can be determined from the measurements since the heat flux at the surface is the same as the heat flux through the test assembly thermal sensors provide the temperature difference between the surface and the adjacent air application of equation 1 then gives measured values for the air film resistances air film resistances taken from the ashrae handbook of fundamentals are used to calculate the air to air r values and u values for a field application this is done because the film coefficients in a test apparatus can differ from those present in a full scale building application table 6 contains measured surface to surface r values for the hybrid assemblies that were tested air to air r values are listed in table 6 for both measured r values and.