Jose Roberto Rodriguez, M.Eng. 2014
Supervisor: Dr. Rodrigo Mora
The Lower Mainland of Vancouver has a unique climate that combines slightly cold temperatures with very humid ambient conditions for most of the year. Hygroscopic construction materials are susceptible to collecting moisture when exposed to outdoor humidity conditions during construction. Furthermore, increasing thermal and airtightness requirements by current codes increases the risk of leaving construction moisture trapped within roof assemblies. Different from other envelope assemblies that have the ability to exchange moisture with either the exterior or the interior of a building, conventional low-slope roofs keep construction moisture trapped within the assembly.
This project proposes a methodology to quantify the actual moisture levels of roofing materials at the time of installation, and analyses the possible implications on the thermal performance and long-term durability of roof assemblies. The science behind hygroscopic materials and their relationship with outdoor conditions are discussed, as well as a literature review of the phenomena of heat and moisture transmission that occurs within the sealed low-slope roof assemblies. Hygrothermal computer software simulations are performed and correlated with available field data to determine typical moisture levels within conventional roofs. Recommendations are made to expand on the data, and to determine the relationship between initial moisture content and installation conditions. Further work is suggested to generate more data that would help determine more suitable or acceptable levels of moisture that can be trapped within conventional low-slope roof assemblies without detriment to the construction in the Lower Mainland. Ample data would improve roof design to ensure acceptable long-term thermal performance and durability.