PROPOR

DOE-2

MOIST

MATCH

HEATING

EQV-WALL

MOIST

Transfer of Heat and Moisture in Building Envelopes

MOIST is a user-friendly, personal computer program developed by the National Institute of Standards and Technology and the Virginia Polytechnic Institute and State University. MOIST predicts the one-dimensional transfer of heat and moisture in building envelopes. A wall, cathedral ceiling, or low-slope roof construction can be easily defined, and the effects of various parameters on the moisture accumulation within layers of construction can be investigated. For example, the effect of climate on moisture accumulation can be investigated by conducting computer runs for different U.S. and Canadian cities. The need for a vapor barrier can be determined; and, if needed, where it should be placed relative to the other materials. MOIST allows the user to vary easily the building materials and their relative placement and predicts the resulting moisture accumulation within each as a function of time for the selected climate. MOIST permits the evaluation of the effect of the water-vapor resistance offered by paint layers, wallpaper, and vapor retarders. Finally, MOIST can be used to produce moisture control guidelines.

The algorithms in the program can predict moisture transfer for the diffusion regime through the capillary flow regime. The program has a provision to account for convective moisture transfer by including embedded cavities which may be coupled to indoor or outdoor air. The program generates a plot on the computer screen of the average moisture content of the construction layers versus time as the program executes. The program generates output files which may be imported into plotting programs for preparing reports.