CONSTRUCTION OF CONTROLLED SPACES

1. any vapor barrier must be continuous, without breaks or tears.
2. all lap joining must be tightly closed. (this is particularly critical when mechanical or caulked joints are used).
3. insulation between vapor barriers can be a potential problem. if construction occurs in humid weather, moisture can be sealed in between the two vapor barriers. Sealed-in water vapor will travel into the controlled space and impose an extra drying load on the drying equipment. this extra load lasts only until the insulation dries out, but meanwhile humidity control is difficult. if a heat source is present (even heat from the sun), serious damage can be caused by the expanding trapped vapor. there have been cases when so-called "non-permeable" materials have split open at a joint because of vapor pressure. examples include a floor or tiled wall that has literally lifted from its mounting surface because the surface was wet during application.
4. final inside vapor barriers should be applied only after the enclosed area has been dried. drying equipment should be used to withdraw as much moisture as possible before the final barrier is applied. of course, without a barrier in place, equipment cannot dry the air to design specifications, but a significant amount can and should be removed before all the vapor barrier material is in place. (Although this strategy is not included in most industrial planing suggestions, the concept of drying the structure before applying the final vapor barrier is a precaution that is often overlooked and can help prevent problems associated with trapped water vapor).
5. all doors, service or personnel, should be weather-stripped or air locked through vestibules if the desired conditions warrant it. any crack or opeingng around a door will admit water vapor.
6. when a conveyor opening or similar elements are used, a drop curtain, shroud, or tunnel will reduce the migration of water vapor.