Starting with a brief introduction on energy efficiency trends and initiatives/programs in the residential construction sector, this report focuses on the causes of, and ways to reduce vapour condensation. It also covers performance of wood-frame building enclosures, specifically walls, traditional vented roofs and relatively new unvented roofs, during laboratory/field testing and service. It confirms that the key to achieving long-term durability for highly insulated walls and unvented roofs in cold and coastal mild climates is to ensure good air tightness and reduce air exfiltration, control indoor humidity, reduce outward vapour diffusion, and keep wood elements warm. For traditional vented roofs in cold climates the key is to ensure good sealing at ceilings, reduce indoor humidity and maintain good attic ventilation. Studies on ventilation reduction and optimization to potentially reduce attic humidity, in coastal mild climates in particular, are also discussed.
Based on the identified knowledge gaps in how to ensure good durability performance of highly insulated wood-frame building enclosure assemblies, the report provides recommendations for future work:
Conduct field testing of highly insulated building enclosure assemblies to further quantify vapour condensation potential under realistic indoor and outdoor conditions in the representative climates in North America.
Inspect older houses/buildings built with high levels of insulation in the building enclosure to assemble service performance data, and summarize solutions to achieving good durability and energy efficiency.
Further improve hygrothermal simulation tools to improve the prediction of moisture and energy performance and thereby the design and construction of highly insulated building enclosure assemblies.
Provide guidelines on durable, buildable and economical building enclosure assemblies to improve the design and construction of energy efficient wood-frame houses/buildings.
The progress related to these items has been reported.