Mathematical Analysis of Practices to Control Moisture in the Roof Cavities of Manufactured Houses - Tapa blanda
Sinopsis
A mathematical model is presented that predicts moisture and heat transfer in ventilated cavities such as attics, roof cavities, and cathedral ceilings. The model performs a transient moisture and heat balance as a function of time of year and includes the storage of moisture and heat at the construction layers. The model includes both molecular diffusion and capillary transfer within the materials. Radiation exchange among the ventilated cavity surfaces is predicted using a mean-radiant-temperature-network model. Latent heat (i.e., the effect of water evaporating from one place and condensing at another place) is distributed within the materials. Airflow from the house into the ventilated cavity is predicted using a stack effect model with aggregated effective leakage areas. Air exchange between the ventilated cavity and outdoor environment is predicted by a semi-empirical model. The relative humidity in the house is permitted to vary during the winter and is calculated from a moisture balance of the whole building.
This mathematical model was used to simulate the performance of a double-wide manufactured house constructed in compliance with the latest HUD Standards. An interior vapor retarder was installed in the ceiling construction and ventilation openings were installed in the roof cavity consistent with the 1/300 rule given in the HUD Standards. The effect of passive and mechanical ventilation, as well as a wide range of other factors on the roof sheathing moisture content was investigated as a function of time. The weekly average moisture content of the lower surface of the plywood sheathing was analyzed in several cold climates, while the relative humidity at the lower surface of the ceiling insulation was analyzed in a hot and humid climate.
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Reseña del editor
A mathematical model is presented that predicts moisture and heat transfer in ventilated cavities such as attics, roof cavities, and cathedral ceilings. The model performs a transient moisture and heat balance as a function of time of year and includes the storage of moisture and heat at the construction layers. The model includes both molecular diffusion and capillary transfer within the materials. Radiation exchange among the ventilated cavity surfaces is predicted using a mean-radiant-temperature-network model. Latent heat (i.e., the effect of water evaporating from one place and condensing at another place) is distributed within the materials. Airflow from the house into the ventilated cavity is predicted using a stack effect model with aggregated effective leakage areas. Air exchange between the ventilated cavity and outdoor environment is predicted by a semi-empirical model. The relative humidity in the house is permitted to vary during the winter and is calculated from a moisture balance of the whole building.
This mathematical model was used to simulate the performance of a double-wide manufactured house constructed in compliance with the latest HUD Standards. An interior vapor retarder was installed in the ceiling construction and ventilation openings were installed in the roof cavity consistent with the 1/300 rule given in the HUD Standards. The effect of passive and mechanical ventilation, as well as a wide range of other factors on the roof sheathing moisture content was investigated as a function of time. The weekly average moisture content of the lower surface of the plywood sheathing was analyzed in several cold climates, while the relative humidity at the lower surface of the ceiling insulation was analyzed in a hot and humid climate.
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