Interior vs. exterior French drain.

An exterior French drain works. So does an interior one. The question is what you're paying for.

Exterior drains require excavating the entire perimeter of your foundation down to the footing — eight to ten feet deep, all the way around the house. Your landscaping is gone. Your driveway, if it touches the foundation, is gone. The membrane and drain tile go in, and everything gets backfilled and put back. The job runs $25,000 to $50,000 in Southeast Michigan.

Interior drains do the same job — capture water at the wall-floor cold joint and route it to a sump — but the work happens inside the basement. We cut a 12-inch channel along the perimeter, lay perforated drain tile in clean stone, and route it to a dedicated pump. The yard is untouched. The cost is a third to a fifth of exterior.

Why don't we always recommend exterior? Because in Michigan, 90% of basement leaks come from hydrostatic pressure pushing water up at the cold joint, not from the wall itself. Interior drainage handles that. The wall isn't the problem.

We made the switch in 2003. Twenty-three years and thousands of installs later, we've never seen a customer who needed exterior excavation that interior drainage didn't solve.