Selection of moisture reference year for freeze-thaw damage assessment of historic masonry walls under future climate: A simulation-based approach

Abstract

Today, there is an increased research effort on improving energy efficiency in heritage buildings through retrofit measures. Hygrothermal simulations tools are often used to assess the long-term performance of building envelopes and determine whether they are suitable for interior insulation. To reduce the high computation time and cost incurred with these simulations, a moisture reference year (MRY) is typically selected based on long-term annual climatic conditions. Simulation results obtained under MRYs are assumed to represent the long-term performance. However, when assessing the risk to freeze-thaw (FT) damage of historic masonry walls, methods selecting climate-based MRYs have failed to represent the actual performance – determined based on results from simulations over the 31 consecutive years. This paper attempts to find an alternative method to select MRYs, based on the hygrothermal simulations of specific constructions. First, a parametric analysis was proposed to identify the parameters that have the greatest influence on FT damage. Then, simulations are performed for a continuous 31-year period and for each single year. A comparison of their results suggests that there is no accumulative effect on the annual freeze-thaw cycles; and therefore, MRYs can be selected as the single year with the 93rd percentile FT damage severity or the worst year commonly found between masonry walls pre and post retrofit. The application of MRYs was then verified for different insulation types and thicknesses. Results showed that simulation-based MRYs are construction and orientation dependent; however, they are reliable to use for retrofitting design decision making.