Analysis of roof systems thermal performance from field data.

摘要

According to the most recent Project Pinpoint, the percentage of new and replacement low-slope roofs in the United States now being insulated exceeds 88 percent. This is dramatic evidence that good thermal performance is a worthy investment and has become an accepted design characteristic of roof systems despite higher initial costs. As the interest in thermal performance increases so do concerns that insulation performance meet design expectations over the life of the roof system. Several widely used standardized laboratory procedures are available for evaluating the thermal performance of insulations. These include ASTM Standards C-177, C-518, C-236, and C-976. Laboratory measurements, while being valuable for product control, are useful as performance indicators only to the extent that they can predict material performance in an in-service roof system. In the last several years field measurements have shown that there are many instances when effects, not readily quantifiable by laboratory measurements, can significantly change the thermal performance of roofs from design values. Examples illustrated in this report are thermal drift in CFC-blown foam insulations, drying of lightweight insulating concrete fills, condensation-evaporation cycling of moisture in fibrous glass insulation, and temperature changes caused by changes in surface solar reflectance. These effects alter the thermal performance of roofs from design values and affect the cost of heating and cooling buildings. 15 refs., 15 figs.