Attic Mold and Basement Moisture

By Nancy Nichols, P.E. | June 27, 2020

What do attic mold and basement moisture have to do with one another?  Everything! Moisture in the basement in the form of unseen and odorless water vapor migrates into the attic via the same pathways as heat leaks.  After water vapor migrates into the attic, it will condense on cold surfaces for certain indoor/outdoor temperature differences.  The resultant moisture provides an ideal environment for mold growth.

There may be other sources of water causing mold in the attic (e.g., ice dams, humidifiers, unvented steam in bathrooms and kitchens, plants, etc.), but we find that basement water (or water vapor) is commonly the most significant contributor to attic moisture.  Typical sources of basement water include roof water, surface water runoff and high ground water table.  The solution may start with improved exterior drainage and sealing the basement walls and floor.  Dehumidification may also be needed but should not be the only remedial measure.  Dehumidifiers can actually draw water vapor into the basement. Mitigation of interior sources of moisture and sealing pathways into the basement should also be considered.

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