Exterior French drains

should only be considered in two situations:

1. During new construction, before backfilling the foundation.
2. When a house is built on high ground, allowing the drain to be led to daylight (a gravity drain), eliminating the need for a sump pump.
   
   

Exterior French drains have limitations: they are exposed to weather and vegetation, which can deteriorate the system over time, and their warranty periods are typically shorter than interior systems. Installing an exterior drain on an existing home can be challenging, especially in areas such as attached garages, sunrooms, or sections built on slabs or crawl spaces.

Capacity differences:

• Exterior systems handle 60–80% more groundwater than interior systems because they collect water entering the ground outside next to the foundation.
•  If a gravity drain is not possible, a sump pit must be installed either outside the foundation or inside the basement. Exterior pits can be 8–12 feet deep, which can be hazardous. Directing this larger volume of water into an interior sump can lead to frequent pumping cycles and may overwhelm the pump’s capacity.
• Interior French drains only collect water that rises from a high water table. Normal groundwater around the foundation does not enter the system.
  
  

A common misconception is that interior drains “invite water into the basement.” This is incorrect. Whether installed inside or outside, if the drain is 1 foot below the basement floor, the groundwater remains 1 foot below the floor level. Properly installed, interior systems control water safely without introducing new risks.