Roof temperatures in simulated attics

Abstract

The degradation of wood treated with fire retardant (FR) chemicals in roof systems is a problem of major national significance. Understanding of this phenomenon is limited by lack of information on how the performance of FR-treated wood in the laboratory correlates to that of FR-treated wood in the field. In this study, five outdoor field exposure chambers were constructed near Madison, Wisconsin, in the summer of 1991. These structures were intended to simulate the batticsc of multifamily structures for which model building codes sometimes allow the use of FR-treated roof sheathing. Interior attic air, exterior air, inner and outer sheathing, and internal rafter temperatures of black- and white-shingled chambers were monitored. Temperatures were measured using thermocouples and recorded over a 3-year period from October 1991 through September 1994 using a datalogger/multiplexer device. Overall, the plywood sheathing in black-shingled roof systems tended to be 10*F to 15*F (5*C to 8*C) warmer during the midafternoon of a sunny day than the plywood in comparable white-shingled roof systems. The maximum sheathing temperatures recorded were 168*F (76*C) for blackshingled roofs and 147*F (64*C) for white-shingled roofs. The results suggest that roof-sheathing plywood and rooftruss lumber temperatures, which are the primary factors that influence thermal degrade of FR-treated materials, are primarily controlled by solar gain rather than attic ventilation or attic insulation. These results are tempered by the fact that the effect of moisture content was not evaluated nor was moisture controlled by attic ventilation.

Citation

Winandy, J. E.; Beaumont, R. Roof temperatures in simulated attics. (Research paper FPL ; RP-543):14 p. : ill. ; 28 cm.