TECHNICAL RESEARCH
INDUSTRY RESEARCH
Temperature, Airflow and Moisture Patterns in Attic Roofs
Description Hygrothermal performance analysis of a ventilated attic is used to study excessive moisture accumulation and durability of the attic structural components. This project builds upon BCIT’s Building Science Centre of Excellence attic airflow research. Using computational fluid dynamics (CFD) and HAMFit 2D hygrothermal modelling, this research provides in-depth insight into the heat, air, and moisture transfers in an attic roof. In addition to climatic conditions, the study considers attic insulation levels, including a highly insulated attic roof case, ceiling airtight- ness levels and roof slopes. Locations in the attic roof system that are susceptible to moisture damage are investigated in detail. The outdoor wind pressure effect on the sheathing moisture content is also studied. Results show that the roof sheathing maintains smaller amounts of humidity under a reduced insulation thickness. In addition, the roof sheathing parts in close proximity to the attic baffle, near the soffit region, are the most susceptible to moisture damage. The effect of ceiling leakage is higher in the upper parts of the sheathing. Impact This research enhances understanding of hygrothermal performance consider- ations for the design and construction of durable and energy efficient attic roof systems. It identifies areas in the attic roof where moisture damage risk is expected to be higher and where extreme temperatures may affect the roof durability.
Status: Report available online at www.bchousing.org Partners: British Columbia Institute of
Technology (BCIT), Natural Sciences and Engineering Research Council of Canada
Audience: Builders, developers, contractors, design
professionals and other industry professionals
80 HOUSING RESEARCH & EDUCATION PROJECT HIGHLIGHTS | JULY 2021
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