Analysis of Moisture Accumulation in Roof Cavities of Manufactured Housing.
Analysis of Moisture Accumulation in Roof Cavities of
Manufactured Housing.
(1077 K)
Burch, D. M.
American Society for Testing and Materials. Airflow
Performance of Building Envelopes, Components, and
Systems. ASTM STP 1255. 1995, ASTM, Philadelphia, PA,
Modera, M. P.; Persily, A. K., Editor(s)(s), 156-177 pp,
1995.
Sponsor:
Department of Housing and Urban Development, Washington,
DC
Keywords:
roofs; housing; attic ventilation; HUD Manufactured Home
Construction; safety standards; mobile homes; moisture
control guidelines; moisture in attics; manufactured
housing
Abstract:
A detailed computer analysis is conducted to investigate
whether moisture problems occur in the roof cavity of
manufactured homes constructed in compliance with the
current Department of Housing and Urban Development
(HUD) Standards for manufactured housing. The current
HUD Standards require a ceiling vapor retarder, but do
not require outdoor ventilation of the roof cavity. In
cold climates, the analysis revealed that moisture
accumulates at lower roof surface and poses a risk of
material degradation. The analysis found the following
combination of passive measures to be effective in
preventing detrimental winter moisture accumulation at
lower surface of the roof: 1) providing a ceiling vapor
retarder, 2) sealing penetrations and openings in the
ceiling construction, and 3) providing natural
ventilation of the roof cavity. In addition, the
performance of a roof cavity exposed to a hot and humid
climate is investigated. The analysis revealed that
outdoor ventilation of the roof cavity causes the
monthly mean relative humidity at the upper surface of
the vapor retarder to exceed 80%. This condition is
conducive to mold and mildew growth.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899