Section VIII – Mold, Moisture, Vapor & Air Penetration

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Mold is actually a family of several species of fungi that can infest damp interior surfaces. They are spread primarily by microscopic airborne spores that are abundant in most environments. These fungi require three conditions to grow: oxygen, a food source, and moisture. Eliminating one of these three elements will keep mold growth in check; however, two of the three are almost impossible to eliminate: oxygen and a food source. Mold will consume any available organic nutrient, especially pollen and common house dust, which are readily available on most interior surfaces and are almost impossible to contain. So, the only one of the three elements over which we have any real control is moisture. To keep mold in check, keep moisture out.

Warning: Some varieties of mold pose a health risk, particularly to people who are hypersensitive to mold. For this reason, mold abatement should only be attempted by trained professionals.


Gypsum board will not withstand exposure to elevated levels of moisture for extended periods. Examples of elevated levels of moisture include, but are not limited to, exposure to rain, condensation, water leakage, and standing water. Some gypsum board exposed to these conditions may not need to be replaced, depending upon the source of the moisture and the condition of the gypsum board being considered for replacement. However, if there is ever any doubt about whether to keep or replace gypsum board that has been exposed to moisture – replace it.

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Assessing the Need for Replacement of Gypsum Board

Replace gypsum board that has been exposed to excessive moisture unless all of the following conditions are met:

• The source of the water or moisture is identified and eliminated.

• The water or moisture to which the gypsum board was exposed was uncontaminated.

• The gypsum board can be dried thoroughly before mold growth begins (typically 24 to 48 hours depending on environmental conditions).

• The gypsum board is structurally sound and there is no evidence of rusting fasteners or physical damage that would diminish the physical properties of the gypsum board or system.

CAUTION: When replacing gypsum board in a fire resistance or sound rated system, take care to ensure that all repairs are consistent with the specific fire or sound rated design initially constructed (gypsum board type, fasteners and their spacing, and staggered joints).


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Recommendations for Drying Conditions

These are general recommendations; for more detailed information, contact a water damage restoration specialist.

• Provide adequate ventilation, air circulation, and drying to minimize the potential for mold or other fungal growth.

• Eliminate the source of water or moisture.

• Remove all damaged gypsum board and other wet materials that are to be replaced from the building to facilitate drying.

• Begin thorough drying of the interior of the building immediately.

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Vapor Penetration

The penetration and accumulation of water vapor into building cavities can lead to mold growth and the deterioration of the building materials through rot or rust. Preventing unwanted vapor penetration is generally accomplished in two ways. The first is to block moist air from entering the building cavity by closing all passages into the building cavity. The second is to install a vapor retarder in the building cavity. However, proper placement of a retarder depends on the local climate.


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Air Penetration

The loss of conditioned air (heated or cooled) from the interior of a building to the exterior is a major source of energy loss. In other words, unwanted air movement through a building will increase energy costs. Air barriers help reduce unwanted air and moisture movement. Gypsum panel products, including interior gypsum wallboard and gypsum sheathing serve as air barriers when properly installed and finished. However, cracks and other openings around exterior doors, windows, plumbing, electrical boxes, etc., provide passages for air to leak in and out of a conditioned space. For this reason, it is important to fill all openings through which conditioned air can escape to the outside with caulk or another appropriate material.

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