Armchair Builder

Tips for a Dry Basement

Exterior Insulation Board: A Dry Basement Component

As a builder, people are always asking me…what’s the best way to guarantee a dry basement?  Sure, you can start with a very good waterproofing on the exterior of the basement wall.  But what about the foundation drainage system?  How can I be sure that it will work during those heavy rain storms?  What can you do to make sure a dry basement…stays dry?

When I am building a home and I know the water table is high in the area and the soil is poor draining (i.e. clay or rock), I typically will add a second sump pump to the basement. For an extra $250, you can add a second crock and pump that will add some redundancy to the system.  Airplanes have redundant systems so why not in the basement of your new home or addition? I add the second sump pump and crock near the entrance of the main sanitary sewer line (if the house is in a location that has sewer treatment).  The main sewer line can act like a small stream during heavy rain events bringing large amounts of water toward your basement (the sewer line sits on a bed of stone that can facilitate the movement of water).  If we place a sump crock and pump near the sewer line entrance, we will increase our chances of maintaining a dry basement.

The benefits of the second sump pump include a backup in case one breaks down and…it gives you twice the pumping capacity during those heavy rain storms. The following list gives some other methods for keeping a dry basement.

  • A good quality waterproofing material properly applied to the exterior of the basement wall and covering the joint between the footing and wall (also consider insulation board on exterior that also acts as a drainage plane for water and protects the waterproofing from damage during backfill operations…see picture above).  This is one of the most critical elements to a dry basement.
  •  Interior and exterior foundation drainage system (i.e. drain tile or equivalent) with bleeders at every 8′.  A bleeder is just a pipe that connects the interior drain to the exterior drain (bleeders come into play when the drain stops working on the exterior or interior…it allows water to bypass problem area)
  • Positive grade around the house (6″ drop for the first 10′ coming out from the foundation)
  • Properly draining downspouts/gutter system, directing water away from the foundation.  Don’t overlook the simple easy elements to a dry basement.
  • 4″ of stone below the basement floor (supports the floor and allows water to migrate to the drains from under the floor)
  • Plastic sheathing under the floor taped at seams (also a critical component to your radon mitigation system so it serves dual purposes)
  • Battery backup sump pump ($350-$500 installed).  It’s a good idea because…what’s a typical byproduct of a rain storm?  Yes…a power outage.  Storms are the biggest threat to a dry basement.
  • Water Alarm set near your sump pump.  These can be purchased for $10-15 and can be setup easily by the DIY’er.  Check out our video, Keeping Your Basement Dry, for more details.
These tips won’t guarantee a dry basement, but they will definitely increase your chances of keeping the water out.  If you are thinking of finishing your basement in the future, definitely follow these tips in your new home building project.  A wise builder once said, “Dry basements are made…not born.”

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