Fpl Roof Temperature And Moisture Model

This paper describes a mathematical model developed by the Forest Products Laboratory to predict attic temperatures, relative humidities, and roof sheathing moisture content. Comparison of data from model simulation and measured data provided limited validation of the model and led to the following conclusions: (1) the model can provide reasonably accurate estimates for temperatures of roof sheathing and attic air, although heat storage effects often cause delay of 1 to 2 h in attic air temperatures; (2) the model can accurately predict the frequency of occurrence of high roof sheathing temperatures (> 120ÃF (49ÃC)) during summer, but accuracy is highly dependent on solar absorptance and emissivity values of the roof shingles; (3) the model consistently overpredicts the extent of night-time cooling from sky radiation losses, leading to predicted temperatures that are too low; (4) treatment of the effect of snow cover is too simplistic, but no better alternatives are apparent for simulating this very complex behavior; (5) the model apparently can predict average moisture conditions in the sheathing with reasonable accuracy, generally within 1% moisture content, when moisture content is not excessively high or low; and (6) hourly moisture behavior is not represented as well as is daily or seasonal behavior, especially for north-facing sheathing. The model would benefit from verification with data that include measured emissivity and solar absorptance of the shingles, addition of thermal mass in attic and roof, better algorithms to calculate direct and diffuse solar radiation, and verification for roof with east--west orientation.

In recent years wood strength researchers have begun to replace experimental unit allocation via random sampling with allocation via sorts based on nondestructive measurements of strength predictors such as modulus of elasticity and specific gravity. Although this procedure has the potential of greatly increasing experimental sensitivity, as currently implemented it can easily reduce sensitivity. In this paper we discuss the problem and we present solutions. Given the existence of nondestructive measurements of strength predictors, our methods can be used to reduce sample sizes. We have written a public domain computer program that implements the methods.

To address the problem of defining actual field temperatures of various wood components in wood-framed roof systems, roof temperatures were monitored in test structures situated in the northern and southern United States (Madison, Wisconsin, and Starkville, Mississippi, respectively). The field exposure structures were intended to simulate the attics of multifamily wood-framed structures for which Model Building Codes sometimes allow the use of fire-retardant-treated roof sheathing. The structures were instrumented to monitor interior attic air, exterior air, inner and outer plywood roof sheathing, and internal rafter temperatures in dry whiteshingled structures and both dry and heavily humidified black-shingled structures. Temperatures were recorded from January 1992 through December 1999 in Wisconsin and from January 1996 through December 1999 in Mississippi. The Mississippi exposure generally induced 5ÃC to 10ÃC higher temperatures than did the Madison exposure, though the difference in annual maximum gbs1-h averagegcs temperature of both exposures was usually no more than 3ÃC to 4ÃC. Overall, black-shingled roof systems tended to be 5ÃC to 10ÃC warmer during the midafternoon of a sunny day than were comparable white-shingled roof systems. Few differences in plywood roof sheathing temperatures were noted between dry and heavily humidified structures. Attic airspace and rafter temperatures were generally 5ÃC to 10ÃC cooler in humidified attics than in dry attics. The major difference in the temperature of wood components in the Wisconsin and Mississippi structures occurred during the winter, when temperatures were as much as 20ÃC lower in Wisconsin.

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