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During warm humid weather, condensation leakage problems plague a “cool” loading dock room of a refrigerated warehouse near Washington, DC. Cold air flows out the base of the room through openings in the gaskets between trucks and open loading dock doors. This creates a stack effect, drawing in warm, humid air through a poor seal between the top of the masonry cavity wall and the roofing system. The warm, humid air condenses in the ribs of the steel deck and the condensate leaks into the building.
During our investigation, I also evaluated the water-vapor transmission through the ethylene propylene diene monomer (EPDM) roofing system by testing the permeance of the three-year-old weathered system and comparing it to a nonweathered EPDM sample, and by analyzing the steady-state water-vapor flow. I found the permeance of the EPDM membrane increased 22%, from 2.58 ng/Pa ∙ s ∙ m2 (0.0449 grains/(ft2 ∙ h ∙ in. ∙ Hg)) for nonweathered EPDM to 3.14 ng/Pa ∙ s ∙ m2 (0.0547 grains/(ft2 ∙ h ∙ in. ∙ Hg)) for weathered EPDM. Steady-state analysis showed that only 0.034 kg/m2/year (0.007 lbs/ft2/year) would flow through this roofing system. This is a very small amount of moisture compared to that being transported by the warm air flow.
The pattern of condensation I saw during my investigation confirmed my theory that the “leakage” is caused by moist air flowing into the roof system and not water vapor transmission through the roof system. Successful repairs were designed and installed that blocked the air from flowing into the edges of the roofing system.
cool storage building, ethylene propylene diene monomer (EPDM) roof, condensation, water vapor transmission, air flow, testing
Associate, Simpson Gumpertz & Heger Inc., Arlington, MA