Using hygrothermal modeling to resolve practical low-slope roofing issues

Within building envelope science, the use of tools to model performance of the building envelope has evolved, and designers and scientists today have a myriad of tools available. Hygrothermal modeling is one such tool and, when used correctly, offers designers and forensic investigators important information about the movement of moisture within the building envelope. This traditional use of hygrothermal modeling is maturing as models are validated with field experience, creating a confidence in the modeling tools and their predictive capabilities. Based on this confidence, application of hygrothermal modeling to a more practical application is an evolution whose time has arrived. With changes in materials and methods, the performance of roofing systems can often times no longer be based on experience alone. Roofing contractors have been confounded by the unexplained and unplanned-for presence of moisture in roofing systems. Although hygrothermal modeling can be used to explain where the moisture came from, we propose that it should be used to prevent its occurrence. Unfortunately, more than 70 % of the roofing market is in reroofing, and oftentimes, a designer is not engaged in the roofing system design. Without the expertise of a designer and given that hygrothermal modeling is not well understood by the roofing industry, its adoption as a tool that can prevent problems has not been widely seen. This paper presents an extensive summary of hygrothermal modeling performed for roofing systems and then shows how the modeling can be used to create simple resources for roofing contractors to reduce the potential for moisture condensation at critical locations within a roofing system. The systems modeled have shown a propensity for moisture accumulation, and the use of hygrothermal modeling to eliminate these problems is a practical application of a building science tool that can greatly improve the durability of roofing systems.