Predicting moisture problems in low-slope roofing

Moisture intrusion is the major reason why low-slope roofing systems fail prematurely. With approximately 75% of all roofing activity being reroofing, the roofing professional is faced with deciding what to do with an existing wet roof on almost a daily basis. This paper describes finite-difference computer modeling that has been performed to address moisture control in low-slope roof systems. Based on a large database of finite difference modeling results, algorithms have been developed that allow the roofing practitioners to simply determine if a roofing system design requires a vapor retarder or if the system can be modified to enhance its tolerance for small leaks. This paper illustrates how modeling results were obtained, describes the process employed to develop the algorithms, and demonstrates how these algorithms can be used to design a moisture tolerant low-slope roof. The range of applicability and limitations of these algorithms is also detailed.