Crawl Space Sump Pump

Throughout the Seattle area, excess water is simply a reality of life.  This water, however much greenery it may provide, becomes a major nuisance when it invades our homes.  Fortunately, many homes in the Northwest are built above crawlspaces, providing a buffer between the saturated ground and the framing of the home.  While this reduces the risk of catastrophic failures, problems still exist. Basements are another story.

How does water enter the crawl space?

Because we’re covering sump pumps, we are limiting our discussion to the liquid state of water.  Water in a vapor state can certainly cause significant problems, but when a sump pump is involved, it is a result rather than a cause.  So how does water enter the crawl space?  Two primary culprits are found, groundwater and rainwater.


  • Water Table.  If you’re exceedingly unlucky, your crawl space may fall below the water table line.  This is the point where the voids in the soil structure become completely filled with liquid water. This water may be removed with a sump pump, however, it will likely require continuous operation.
  • Spring.  Although quite rare, occasionally a spring is found beneath a crawlspace.  This occurs when pressure from an aquifer forces water back up to the surface.  As with a water table, this requires continuous sump pump operation.
  • Capillary Action.  For most homes in Washington, this is the primary cause of wet crawl spaces.  The movement of water through confined pores by the influence of surface tension.  What does this mean?  The same property that allows water to travel up a paper towel similarly allows water to travel upward through soil.  In your home, even though the water table may be several feet below, capillary action can pull gallons of water directly into your crawl space.


  • Why?  Pretty obvious, it rains a lot in Seattle and the water needs somewhere to go.  Problems arise when rain water saturates the soil immediately surrounding the crawl space.  Your crawl space is nothing more than a giant hole dug in the ground.  If this ground becomes saturated with rainwater, it will seek a repository.  Your crawl space fits the bill perfectly.
  • Downspouts.  The absolute first step in addressing rainwater issues is to direct the downspouts as far from the perimeter of the foundation as possible.  Remember, your roof collects a tremendous amount of water during a storm.  If your downspouts merely dump this at your foundation wall, the water will inevitably flow towards the most receptive location, your crawl space.

What is a crawl space sump pump?

A crawl space sump pump consists of a perforated basin, set below the soil level.  Inside of this basin is the actual pump.  As water collects in the crawl space it should gather in the basin, and the pump should be activated.  The pump will then direct this water through a drainage pipe into the sewer system, or to an area outside of the home, where it will not find it’s way back in.