Concept
French Drain
What it is
A french drain is a trench filled with gravel and a perforated pipe that carries water away from where you don’t want it, to where you can let it go. On a flip, it’s usually the fix for water that’s moving toward the foundation from uphill, from a saturated yard, or from a driveway that slopes the wrong way.
You don’t see a french drain after it’s installed. You cover it with fabric and soil. What you do see is a dry basement, a yard that doesn’t pond, and a crawlspace that stops growing mold. For about $3K to $8K in most markets, it’s one of the highest ROI fixes in the whole rehab.
Why it matters
Water intrusion is a deal killer if you ignore it, and a trivial fix if you catch it. A wet basement listed in MLS photos loses buyers instantly. A crawlspace with standing water flunks the home inspection and reopens the negotiation after you thought you were done. A yard that doesn’t drain points inspectors straight to the foundation, where real money lives.
I’ve had deals where the whole margin went to a $20K foundation repair that a $4K french drain, installed two years earlier, would have prevented. That’s the fear tax on water. Know what you’re looking at.
How it shows up
Walk the property twice if it’s been raining. Look at the grade. Does the yard slope toward the house or away? Is there a hill above? Are there stains on the foundation blocks at ankle height? Is the crawlspace vapor barrier dry? Are the splash blocks at the downspouts actually doing their job?
If the answer on any of those is bad, a french drain is probably in scope. Run it along the uphill side of the house, outside the footing, tied to a daylight discharge or a sump. Add a surface collection basin at the corner if there’s a driveway or sidewalk funneling water. The work is half a day for a crew with a mini-excavator.
Don’t let a contractor sell you a full foundation waterproofing package when a french drain is the real fix. Exterior drainage is always the first line of defense. Interior waterproofing is what you do when the exterior can’t get there.