Dose-response simple isopleth for mold (DR SIM): A dynamic mold growth model for moisture risk assessment

A new mold growth model was developed to aid in moisture risk assessment of wood-based building assemblies. This proposed simple model relies on several features common to existing mold growth models but combines them in a new way with improved predictive power. Structurally the model is based on a dose-response relationship. Hygrothermal conditions conducive to mold growth are represented using a mold germination isopleth, i.e., a critical relative humidity curve as a function of temperature. The dose at a given time step depends on the difference between surface relative humidity and the critical relative humidity. Doses are accumulated over time and a sigmoidal function relates cumulative dose to predicted mold rating. During unfavorable conditions, the predicted mold rating does not decline; rather, it remains constant and again increases once favorable conditions resume, subject to a recovery period. The model parameters were optimized using a large database of laboratory growth results obtained from the literature. The model was shown to have improved predictive power compared to an earlier model, and to be consistent with available field data. A key model feature is the ability to capture numerically the stochastic nature of mold growth using a deterministic mathematical form. The Dose-Response Simple Isopleth for Mold (DR SIM) model thus provides a useful tool for detailed moisture risk assessment using hygrothermal simulation or field data inputs of temperature and relative humidity.