A method of predicting and communicating transient hygrothermal behavior of an installed building component in a building wherein an interior environment of the building is materially affected by an environment exterior of the building, includes: defining a performance characteristic of the building component that is affected by transient hygrothermal behavior of the building component; defining exterior and interior climatic factors that affect the defined performance characteristic wherein the interior climatic factors are a function of the exterior climatic factors; and defining one or more non-climatic factors that affect the defined performance characteristic. Inputting these factors into a transient hygrothermal simulation software program to create a software model for performing simulations which predict changes in the defined performance characteristic, as a function of time, that are compared with a threshold performance characteristic value, to provide a user guide.