Towards energy-Efficient homes: Evaluating the hygrothermal performance of different wall assemblies through long-term field monitoring

• Wood stud is a thermal bridge on north walls but a thermal mass on west walls.
• Air cavity in spray foam panels shows contribution to high thermal performance, and does not generate negative convection effect.
• Thermal resistance of panel inversely correlates to material moisture levels within each layer of the panel.
• Spray foam displays high resistance to moisture migration.
• Rigid insulation at outside layer of the wall does not prevent moisture migration, but creates humidity buffering effect inside the cavity.

There is an interest in increasing the energy efficiency of residential housing and sometimes achieving net-zero structures. Effective materials such as spray urethane offer benefits in terms of greater thermal resistance as well as reduction in uncontrolled air leakage. Increased envelope resistance without greatly increasing wall thickness can be a positive feature for a low-energy structure. In this paper, potential hygrothermal performance of five wall panels with different insulation configurations is studied by field experimentation. The five configurations of insulation materials are fibreglass, spray foam, fibreglass with Structural Insulated Sheathing, spray foam EPS rigid insulation, and fibreglass with EPS insulation. The panels are installed side-by-side in a test house; thermocouples and relative humidity sensors are installed. The thermal performance of the panels, humidity levels inside wall cavities, and risk of mold growth are investigated. For further investigation, four homes are constructed, each with one of four potential wall configuration, and studied under occupancy. The experimental results from the building science “building physics” point of view are obtained: wood stud is a thermal bridge on north walls but a thermal mass on west walls; and air cavity in spray foam wall does not generate negative heat convection but increases wall insulation.