Computer Analysis of the Moisture Performance of Roof Constructions in the U.S.DOE Moisture Control Handbook

摘要

A new mathematical model, called the MOIST Attic Model, that predicts thetransfer of heat and moisture in ventilated or unventilated roof cavities is presented. The model includes both molecular diffusion and capillary transfer within the materials and also calculated the indoor relative humidity, the ceiling air leakage rate, and the roof cavity ventilation rate at hourly time steps. This computer simulation model can be used to assess the moisture performance of open attics as well as cathedral ceilings. In the present study, the model is used to predict the moisture performance of a current practice site-built prototype house with 5 different roof designs constructed in compliance with the U.S. DOE Moisture Control Handbook in cold (heating) mixed, and cooling (hot and humid) climates. For each of the 15 roof designs, attention was focused on the peak values of the plywood roof sheathing moisture content and the relative humidity at the bottom of the insulation adjacent to the various ceilings where mold and mildew might grow. Findings of the study regarding the moisture performance of the 15 designs, as well as roof design suggestions, are presented along with recommendations for further study.