Reliability of Moisture Reference Year (MRY) selection methods for hygrothermal performance analysis of wood-frame walls under historical and future climates

Hygrothermal simulations can be used to evaluate the hygrothermal response of building envelope to the effect of climate change. However, to account for the uncertainty in projected future climates, a large number of simulations are required. To reduce computational time, hygrothermal performance of walls is typically evaluated using Moisture Reference Year (MRY), which can be selected based on climate-based indices. This study investigated the reliability of climate-based indices by comparing to the response-based indices obtained from simulations using two methods. Firstly, the direct correlation between two indices is calculated using coefficient of determination (R-2). Second method focuses on evaluating the reliability of climate-based indices in ranking the years in terms of moisture severity compared to that based on simulations. Four climate-based indices: Climatic Index (CI), Moisture Index (MI), Severity Index (I-sev) and annual WDR and three response-based indices: Mould Index, Moisture Content and RHT index are investigated. In general, R-2 between two indices is weak (range of 0-0.79) with highest being 0.79 (between maximum mould index and MI) for stucco cladding wall facing default orientation under historical climate in Calgary. With ranking analysis, the accuracy using climate-based indices in ranking all years is low with some improvement in ranking the first three worst-years. CI and MI perform well and I-sev works for north facing walls for cities like Ottawa and Calgary but fails for Vancouver. To have a reliable assessment of moisture risks, further research is needed to improve existing or develop a new climate-based index specific to Canadian climate.

Automated summary

Hygrothermal simulations can evaluate building envelope response to climate change, but uncertainty in projected climates requires multiple simulations. Using Moisture Reference Year (MRY) can reduce computational time, but reliability of climate-based indices in ranking moisture severity is low. Further research is needed to improve or develop a new climate-based index specific to Canadian climate for reliable moisture risk assessment.