What an interior French drain actually costs.

Most homeowners we meet have already gotten two or three estimates for an interior French drain, and they range wildly. The same basement gets quoted at $5,500, $11,000, and $24,000 by three different contractors in the same week. That's not a market problem — it's a transparency problem. Here's what actually goes into the price, and what you should be paying for a typical Southeast Michigan home.

The base scope of an interior French drain is straightforward. We jackhammer a 12-inch channel along the wall-floor joint, lay perforated PVC drain tile in clean stone, tie it to a sealed sump basin, and cap the channel with fresh paintable concrete. That's the work — and it scales linearly with the perimeter being treated. For a 1,200 square foot basement (roughly 140 linear feet of foundation), the base install is usually $55 to $80 per linear foot, fully installed.

That puts the base perimeter drain in the $7,700 to $11,200 range for a typical 1,200 sq ft basement. From there, the line items that move the total are predictable. A battery-backup sump pump system adds $1,200 to $1,800. Upgrading from a builder-grade sump basin to a sealed radon-ready basin adds about $400. Bleeder holes through block walls (essential for any block foundation) add about $5 per hole and there are usually 20–30 of them. Lifetime transferable warranty paperwork: included.

Where it gets expensive — and where the $24,000 quote comes from — is when contractors price exterior excavation instead of interior drainage. Exterior excavation involves digging down to the footing around the entire perimeter from the outside, applying a membrane, installing drain tile in stone backfill, and replacing landscaping. For most homes it runs $18,000 to $35,000 and disrupts driveways, walkways, and decks. It's the right call for severe foundation damage, but for 95% of wet basements, interior drainage produces the same dry basement at a third of the price.

What pushes the interior price up legitimately: thicker than 6-inch concrete slabs (more jack-hammering, more replacement), finished basements that require careful protection of walls and floors, basements with severely limited access for materials and waste, and partial systems where corner work creates more transitions than a continuous run. None of these should double the price — but they explain a $11,000 estimate vs. an $8,000 estimate on similar homes.

What's NOT included in most reputable interior drainage quotes — and worth confirming on every estimate — is reinstallation of any finished basement materials we have to remove (drywall, paneling, carpet pad). We don't put it back; we put the basement back to bare. Restoration is a separate trade and should be quoted by a finish carpenter or general contractor. Beware quotes that include "restoration" as a vague line item — that's where margin hides.

A representative full-system example for a 1,200 sq ft Southeast Michigan basement: $9,200 for the perimeter drain (about 140 linear feet at $66/ft installed), $1,600 for the sealed sump basin and Zoeller-grade primary pump, $1,200 for the battery-backup pump and deep-cycle battery, $200 for bleeder holes, and a written lifetime transferable warranty. Total: $12,200. That's the number to compare against.

If you have an estimate significantly above or below those numbers, ask for it line-item. Either you're paying for legitimate site complexity, or you're paying for someone's quarterly sales target. We give written estimates we're happy to be compared against any other contractor's bid — call (586) 709-5210 or request one online.