Transcription of EEM-00259 Permeability of Common Building Material to ...
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EEM-00259 Permeability of Common Building Material to ...
Permeability of Common BuildingMaterial to Water VaporWHAT IS A PERM RATING?If a Material has a perm rating of , we know thatin 1 hour, when the vapor pressure difference be-tween the cold side and the warm side of the materialis equal to 1 inch of mercury (1" Hg), 1 grain of watervapor will pass through 1 square foot of the grain of water is equal to 1/7000 of a pressures depend on the temperature andrelative humidity (RH) of the air as temperatureand RH go up, vapor pressure gets higher. Thegreater the vapor pressure differential across orthrough a Material , the greater the tendency for watervapor to migrate from the high pressure side to thelow pressure OF Material THICKNESSThe perm ratings given are for stated thicknesses ofmateria
If a material has a perm rating of 1.0, we know that in 1 hour, when the vapor pressure difference be- ... Plaster on plain gypsum lath, with studs 0.75 20 Gypsum wall board, plain 0.375 50 ... Polyester, glass fiber reinforced sheet 0.048 0.05 THERMAL INSULATIONS Air still 120 Cellular glass 0 Mineral wool, unprotected 116 ...
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