Development of a moisture risk index for wood-frame walls

Abstract

This paper describes ongoing research toward the development of a moisture risk index that is intended to give a quantitative indication of the risk of moisture performance issues for different wood-frame wall assemblies in different climates. The concept is like a Home Energy Rating System Index but for moisture performance of a wall assembly rather than whole house energy performance. The moisture risk index is envisioned as providing more granularity than existing pass/fail criteria or green/yellow/red risk assessments while requiring less computational effort than full probabilistic analysis. Hygrothermal simulations and post-processor models for damage functions provide the core quantitative outputs that are used to construct the moisture risk index. Simulations are informed by field and laboratory data and include vapor diffusion, air leakage, and wind-driven rain loads. Damage functions include mold growth, fungal decay of wood, and corrosion of metal fasteners. The moisture risk index is based on scaling up the numerical outputs for the different damage functions, with an intended range from zero for the best performing (lowest risk) case to 100 for the worst performing (highest risk) case. The index will thus provide information about moisture risk that is easily understood by the building design and construction community, with the ability to illustrate how changing certain design features can mitigate risks.

Citation

Glass, Samuel V.; Boardman, Charles R.; Farkas, Natalia; Zelinka, Samuel L.; Yeh, Borjen; Neupane, Kamal. 2025. Development of a moisture risk index for wood-frame walls. In: Berardi, U., ed. Multiphysics and multiscale building physics. Proc., 9th International Building Physics Conference (IBPC 2024). Vol. 1: Moisture and Materials. Toronto, Ontario, Canada. July 25-27, 2024. Lecture Notes in Civil Engineering. Vol. 552. Singapore: Springer Nature: 303-310. https://doi.org/10.1007/978-981-97-8305-2_42