Why is mold growing in my crawl space?

By · February 13, 2010 · Filed in Consumer Q & A's

Mold cannot grow without moisture or high humidity, so a thorough investigation is necessary to determine the cause of elevated moisture and water in the crawl space. In most cases, several minor conditions have contributed to creating a major problem:

  • Gutter and downspout extensions (a concrete splash block does not count). Here are the numbers: for every 1500 square feet of roof and inch of rain, 1000 gallons of water are channeled off of the roof. If the gutters do not catch the water, or the downspout extensions do not carry the water at least 6 to 10 feet away, all of that rain can make its way into the crawlspace
  • The drainage of the yard can slope toward the house and allow rain water to run into the crawlspace
  • Condensation on the ductwork, as described here, can contribute to high humidity and water puddles in the crawlspace
  • HVAC duct can get damaged or loosened and create a crack which allows the wood components to be cooled, which creates condensation in the humid crawlspace
  • The condensate drain from the HVAC unit can deposit up to 20 gallons of water per day and is sometimes dumped at the edge of the foundation, or worse, into the crawlspace
  • Many plumbing leaks in the crawlspace have been found after they have created some damage
  • A crack in the foundation wall or exterior wall sealant can allow excess ground water to enter the crawlspace
  • Rain penetrations through the building envelope such as the seam where the porch joins the house, window and door openings, improperly installed J-channel on siding, inside corners, or unsealed building exteriors
  • Dryer vents have been found ducted into the crawlspace and can introduce warm, humid air in addition to the lint
  • An inadequate or nonexistent vapor barrier can allow excess ground moisture to evaporate into the crawlspace
  • Inadequate foundation vents or leaving them closed in the summer can hold excess humidity in the crawl space
  • A low clearance crawlspace does not provide as much air space to “dilute” any excess humidity in the crawlspace
  • An underground or wet-weather spring in the crawlspace can be an explanation after other solutions have been exhausted

For more information on water damage or mold remediation, click here

For more information on air duct cleaning and duct repair, click here

For more information on indoor air quality, how mold might make you sick, allergies and health, click here

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