A research study was conducted to investigate the risk of condensation and mold growth in 2x6 wood-framing wall assemblies associated with increasing the thermal resistance (R-value) of cavity insulation for various scenarios of exterior insulation products. Based on the current construction practices, a set of three wall assemblies with different types of exterior insulation systems were chosen for field study with different R-values. In the first phase of this study, the hygrothermal model was benchmarked against the test data of full scale wood-farming wall systems. The predications of the model were in good agreement with the test data. Thereafter, the model was used to conduct parametric study to assess the risk of condensation of these wall assemblies when they were subjected to different air leakage rates for various climate zones. Both the numerical results and the field monitoring data showed different behaviours of exterior insulation strategies. The results of the hygrothermal performance were expressed using the mold index criteria, which allowed sufficient resolution to assess the risk of moisture condensation and related risk of mold growth in the wall assemblies. The results showed as well that adding exterior insulation of different water vapor permeance has resulted in lower risk of condensation and mold growth than the reference wall system (i.e. without exterior insulation).
Buildings XIII: Thermal Performance of Exterior Envelopes of Whole Buildings.