Computer Analysis of Wall Constructions in the Moisture Control Handbook.
Computer Analysis of Wall Constructions in the Moisture
Control Handbook.
(2831 K)
Burch, D. M.; Saunders, C. A.
NISTIR 5627; 70 p. May 1995.
Available from:
National Technical Information Service
Keywords:
building technology; walls; construction; moisture;
computer models; material degradation; Moisture Control
Handbook; moisture transfer model; mold and mildew
growth; vapor retarders; vinyl wallpaper; wall
construction
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.
