There are only two times an exterior French drain will make sense: 

  1. During new construction prior to back-filling the foundation. 
  2. If a house is constructed on high ground and the French drain piping can be led to daylight. This is also called a gravity drain. 

Why Interior French Drains?

An exterior French drain has limited abilities and limited warranty periods. Weather and vegetation can deteriorate an exterior system but will not affect an interior French drain. If you are installing an exterior French drain several years after the home has been built, there will be areas in most homes that cannot be accessed. For example, attached garages, sun rooms, attached sections of home that are built on a slab or crawl.

Exterior Drain Systems

Exterior drain systems will carry a much larger water volume then an interior system (60 to 80% more ground water). Water that enters the ground outside, next to a home, will seep into the earth, flow towards the foundation and run down the foundation walls into the exterior French drain piping. This water does not go into the drain pipes of an interior French drain. Only water that raises up from a high water table on an interior drain system will go into the interior piping. 

No Gravity Drain? No Problem!

What are the options to remove water on an exterior system if a gravity drain cannot be installed. Option one would be to install an 8 to 10 ft deep sump pit on the outside. We find these exterior pits to be dangerous and not a great option. 

The second option would be to install an interior sump pit for water to drain into. Because of this, you would have 60 to 80% more water in your interior sump pit than you would if the French drain was installed on the inside. People often feel the interior drain system is inviting water into their basement. This analogy is completely incorrect! If French drain pipes are installed 1 ft below the basement floor on the interior or the exterior, the water level in the ground, under the basement floor will still be 1 ft below the floor.

Iron bacteria; Clogs sump pump discharge and French drain system piping. With the proper design and maintenance, a French drain can last a lifetime

Interior and Exterior Drain Solutions In New Jersey

Still deciding if you need exterior or interior French drains? Turn to the experts at Basement Waterproofing Solutions. Since 1961, we have serviced New Jersey residents with dry basements and quality service. 

For more information about securing your basement with custom waterproofing systems, give us a call or fill out our online form to request a free, in-home estimate.