Effects of Radiant Barrier
on Shingle Temperatures
Comparative Summer Attic Thermal Performance
Danny S. Parker and John R. Sherwin
Florida Solar Energy Center (FSEC)
The summer attic thermal performance of six roofs has been measured at a heavily instrumented test site, the Flexible Roof Facility (FRF), which is a 1,152 ft² (107 m²) building with six roof adjacent test cells that are heavily insulated from each other. Some 233 channels of data were obtained; this includes 20 temperature measurements per cell, extensive meteorological conditions, surface and tower wind speeds, and attic humidity and roof surface moisture accumulation. The data were collected over the ASHRAE definition of summer (June – September) to compare the cooling season thermal performance of roofing systems. Six different roof types were evaluated, with variations in color, ventilation, roof mass, and the use of radiant barrier systems (RBS). The tests show that roof system reflectivity greatly influences attic summer temperatures.
As part of the evaluation, we examined how much black asphalt shingle surface temperatures were elevated by the presence of a radiant barrier. This is an oft expressed issue with shingle manufacturers, concerning that elevated temperatures will reduce product life. Figure 9 shows the measured surface temperature of the shingles on June 16, 1997, on the reference cell (#5) and those on cell #3 with an RBS and 1:300 ventilation.
Figure 9. Measured shingle surface temperature elevation of cell with radiant barrier system versus reference test cell on June 16, 1997. At peak, the temperature of the shingle surface on the roof of the attic with the RBS was 5ºF greater than that on the reference cell.
The plot shows a maximum increase in the shingle surface temperature of 6.2ºF (3.4ºC). The maximum shingle temperatures measured over the course of the summer were 179.3ºF (81.8ºC) with the standard roof and 183.8ºF (84.3ºC) with the RBS.
This work was sponsored by the Florida Energy Office in support of the Building Design Assistance Center. Their assistance is gratefully acknowledged. Special thanks to the Monier Tile Company and PDF Roofing for supplying roofing materials for the experiments. At FSEC, Armin Rudd assisted with the testing to evaluate the cell ventilation areas and Philip Fairey, Lixing Gu and Muthusamy Swami provided suggestions on the instrumentation. David Beal assisted with the project data acquisition system. (This test also addresses other issues which are not pertinent to the shingle temperature question. The sections concerning these issues were deleted from this reprint and are so indicated by the series of arrows shown below.)
Presented at: The 1998 ASHRAE Annual Meeting June 20-24, 1998, Toronto, Canada