Abstract:

A computer model, called MOIST, is used to investigate the moisture performance of recommended wall constructions given in the Moisture Control Handbook (1991). These wall constructions are intended to minimize moisture accumulation, thereby preventing material degradation, mold and mildew growth, and loss in thermal performance. For the heating climate (northern United States) and mixed climate (central United States), all the wall constructions in the Moisture Control Handbook were found to perform satisfactorily. That is, when the surface relative humidities of the construction layers were plotted versus time of year, the peak relative humidities were always found to be within acceptable limits that preclude material degradation and mold and mildew growth. For the cooling climate (south-eastern United States), one of the walls had risk of mold and mildew growth behind an interior vapor retarder. During the summer, moisture from the outdoor environment diffused inwardly into this construction. Upon reaching the interior vapor retarder, moisture was significantly retarded and accumulated, thereby causing the surface relative humidity to rise above the critical 80% level for mold and mildew growth. An interesting finding was that moisture accumulated during the winter at exterior layers having low permeability, thereby giving rise to relative humidities above a critical level (80%). However, this moisture accumulation occurred at relatively low outdoor temperatures, which would slow mold and mildew growth. For a cooling climate, a permeable wall (i.e., without vapor retarding layers and low-permeability materials) was found to perform satisfactorily. During both winter and summer periods, moisture passed through the construction and did not significantly accumulate within construction layers.

• moisture control, moisture management : computer analysis

1. A computer analysis of the moisture performance of roof constructins in the U.S. DOE Moisture Control Handbook
2. A mathematical analysis of moisture and heat transfer in the roof cavities of manufactured housing
3. A prarmeteric study of wall moisture contents using a revised variable indoor relative humidity version of the "MOIST" transient heat and moisture transfer model
4. An analysis of moisture accumulation in the roof cavities of manufactured housing
5. Empirical validation of a transient computer model for combined heat and moisture transfer
6. Experimental verification of a moisture and heat transfer model in the hygroscopic regime
7. Heat and moisture transfer in wood-based wall construction: measured versus predicted
8. Indoor ventilation requirements for manufactured housing
9. Manufactured housing walls that provide satisfactory moisture performance in all climates
10. MOIST: A PC program for predicting heat and moisture transfer in building envelopes, Release 3.0
11. Water vapor permeability measurements of common building materials
12. Water vapor sorption measurements of common building materials
13. Water-vapor measurements of low-slope roofing materials  

1. Manufactured housing walls that provide satisfactory moisture performance in all climates
2. Test procedures for advanced insulation panels