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Analysis of Moisture Accumulation in Roof Cavities of Manufactured Housing.


pdf icon 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.