This report is an engineering analysis of the application of a polyvinyl chloride (PVC) membrane-type roofing system installed over expanded polystyrene (EPS) insulation retrofitted upon an existing office roof. An extensive economic evaluation is presented in regard to the energy savings attributed to the increased amount of insulation and the subsequent decrease in heat transfer through the roof.

The original four-ply asphalt built-up roofing system had an R-value of approximately 1.2 K · m²/W (6.9°F · ft² · h/Btu) and was beginning to leak in a few locations after being in place only five years. A decision was made to add more insulation due to the excessive heat loss through the roof, especially since the space between the ceiling and roof serves as the return-air plenum. The load limitations on the original roof restricted the alternatives to only a few options, including fiberglass batts above the ceiling panels, bead-board insulation with a PVC or butyl-based waterproofing membrane over the original roof, or removing the existing built-up roof and applying a similar type roof over additional insulation. After an extensive evaluation, the new PVC roof/insulation system was installed during the summer of 1980 with no inconvenience to the office employees.

An economic evaluation has been made based upon historical energy consumption and weather data collected since the office was completed in 1975. Although data are still being collected and analyzed, the preliminary results show that, on an equivalent degree-day basis, the electric resistance heating system used approximately 33 percent less energy for the seven-month period 1 October 1980 through 30 April 1981 compared with the same period for the year prior to retrofit. This equates to an average savings for this seven-month period of 8015 kWh/mo in heating the 1433 m² (15 425 ft²) office building.