MIL-HDBK-1001/SA
preference for vapor retarder location is close to the indoor surface.
4.2.1.4 Application. Pay particular attention to the manner of installing and sealing the vapor retarder material. The design should also consider damage of the vapor retarder both during construction and operation of the building.
4.2.2 Ventilation. Since it is possible that some moisture will accumulate in the insulation, allow escape of the moisture by providing means for ventilation. In the case of wood frame residential type construction with attics, a variety of methods
are commonly available to allow moisture which passes through the ceiling insulation to escape to the atmosphere. With low slope roof construction, other methods for ventilation are required. This approach can be called a self-drying system.
4.2.2.1 Below Insulation. Using boards or sheets with perforations or slots underneath low slope roof deck insulation will allow moisture to escape from the roofing system to the outdoors or indoors.
4.2.2.2 Above Insulation. Ventilation above the insulation in low slope roof decks can be accomplished either by using edge vents or top vents. Top vents penetrate the membrane and will increase the potential for leaks. Top vents, if used, should be spread uniformly throughout the roof area. Use caution when applying ventilation above or below insulation, because the same paths that allow moisture to escape will also allow moisture to enter if the vapor pressure differential is reversed. Top venting should not be used over insulation having limited moisture movement capability, such as plastic foams.
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