How Dry Should a Basement Be?

basement water damage

In many cases, a dry basement doesn’t happen naturally. In fact, basements are almost a laboratory setting for the accumulation of humidity and moisture. Ideally, basement humidity should be kept below 50%. Factors working against maintaining a dry basement include:

  • Soil moisture exuding upwards through the foundation
  • Significant condensation as warm moist air contacts chronically cool basement walls and floor
  • Leaky or “sweating” plumbing pipes routed through the basement
  • Cracks in the foundation wall that admit groundwater seepage, particularly during the summer rainy season
  • Overflowing roof gutters or downspouts that are too short
  • Running clothes washing machines and driers in the basement

When a dry basement becomes chronically wet:

  • Moisture plus the unventilated basement environment provides ideal conditions for the growth of toxic mold that may continuously contaminate the living spaces above
  • Damp basements are often a source of musty odors that infiltrate the house
  • Household systems, including the furnace and main electrical panel, are frequently located in the basement and may be deteriorated by moisture exposure
  • Pre-sale inspections include inspecting and verifying a dry basement; a wet basement may discourage prospective buyers and/or attract lower offers

Creating a dry basement—and keeping it that way—requires a multi-faceted approach:

  • Purchase a hygrometer to determine moisture content inside the basement.
  • Have a plumber inspect pipes routed through the basement and repair leaks and/or insulate pipes that sweat.
  • Locate and repair cracks in basement walls that admit groundwater. Apply waterproofing paint to all walls to reduce micro-seepage.  
  • Install a sump pump in the basement floor to remove rising groundwater and reduce pressure against the underside of the foundation.
  • Make sure roof gutters are unobstructed and not overflowing during rain.  Gutter downspouts should discharge water at least three feet from the house.
  • Buy a dehumidifier sized for the square footage of the basement. The best choice is a model that integrates a hygrometer and automatically maintains the desired humidity setting at all times. Run the humidifier drain line into a basement drain.
  • Properly vent a clothes dryer installed in the basement to the exterior of the house.

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