Issue link: https://hi.iaq.net/i/248503
www.epa.gov/iaq/moisture Table 4-1 Continued SYMPTOMS Condensation MOISTURE PROBLEM POTENTIAL CAUSES DESIGN Warm, moist outside air enters enclosure through cracks and holes during warm, humid weather(b) Air barrier omitted from building design Warm, moist indoor air leaves enclosure through cracks and holes during cold weather(c) Air barrier omitted from building design Building design did not call for positive pressure operation of the building CONSTRUCTION Controls poorly implemented during construction (e.g., concrete block left out of a soffit area) Air barrier installed poorly Holes cut in well-installed Air barrier detailed for attic air barrier to permit passage of wire, conduit assembly is impossible to install or ducts Building designed to operate at positive pressure in an extremely cold climate Vapor barriers installed improperly in exterior walls Vapor barrier specified on both sides of a wall assembly Vapor barrier specified on interior surfaces in hot, humid climates Non-vented or poorly vented moisture sources (e.g., swimming pools, spas, aquariums, dishwashers, combustion devices, kitchens and showers) Delamination Improper curing HVAC system design omitted exhaust ventilation for moisture sources Wet materials enclosed in building assemblies Moisture-sensitive materials shown touching porous materials that are likely to get wet Insufficient exhaust ventilation specified in HVAC system design No values for moisture content or emission given in the specifications O&M Failure to reseal access holes cut through an assembly Changes in HVAC system operations cause building to run at positive pressurization Unintentional vapor barriers such as vinyl wall covering, mirrors or blackboards installed on inside of exterior walls in hot, humid climate (can create a vapor barrier on the cold side of the wall) Vinyl wall covering, mirrors or blackboards added on inside of exterior walls in hot, humid climate (can create a vapor barrier on the cold side of the wall) Exhaust duct leaks Broken belt in a fan Poor balancing on multiple-inlet exhaust systems Clogged exhaust grilles or ducts Exhaust dampers closed Flooring placed on slab while it is too damp Vapor emission tests on slab may not have been conducted This problem may also occur during the bidding, contract negotiation or value engineering phases of a project when, for example, different air conditioning equipment is substituted for the equipment called for in the design. (a) The air leak may be due to holes in the enclosure made by occupants, contractors or maintenance personnel, or it may have been caused by changes in the control sequence of outdoor air and exhaust systems. (b) (c) The problem of indoor condensation can be greatly aggravated if there are large sources of humidity inside the building. 89