Three kinds of French drain
People use the name for several different systems, so it helps to know which one a contractor is proposing.
- Interior perimeter drain: under the basement floor along the walls, feeding a sump pump
- Footing drain: outside, at the base of the foundation, installed during excavation
- Curtain drain: outside, shallower, across a slope above the house to intercept water before it arrives
Curtain drains on hillside lots
For houses below a slope, a curtain drain can be one of the most useful fixes. The contractor digs a trench across the hill uphill of the house, lines it with filter fabric, lays perforated pipe in clean stone and runs it around the house to a spot downhill where the water can safely come out. Groundwater and surface runoff moving down the slope fall into the trench and get carried away before they reach the foundation.
A curtain drain needs a place to discharge. On a hill, that is usually easier than on flat ground, but the water has to end up somewhere that does not harm a neighbor or wash out a slope. Rock in the trench line can raise the cost.
Interior perimeter drains
Inside, the crew cuts a channel in the floor along the walls, digs down beside the footing, sets perforated pipe in stone and slopes it to a sump pit. A dimpled membrane on the wall guides water from cracks and joints down into the drain. For block walls, small holes drilled into the lowest course let water trapped in the hollow cores drain out. Fresh concrete closes the trench. In Ossining's many sloped lots, some homes need the drain along only the uphill walls.
What to compare in bids
Compare linear footage, pipe type, stone, whether filter fabric is used, whether the system includes cleanouts, how the concrete is finished and whether a pump and battery backup are included. For outside drains, ask where the outlet will be and how it will be protected from clogging and from being crushed by lawn equipment.
Living with the work
Interior drains mean a day or two of cutting and digging inside, with dust and noise, and stored items moved off the walls. Curtain drains mean a trench across part of the yard, and the lawn will need time to grow back. Ask how long the work will take and what cleanup and restoration are included in the price.
Typical French drain costs
National figures from Fixr. Not quotes.
| Job | Typical range |
|---|---|
| French drain, most projects | about $2,800 to $6,500 |
| Interior drain, per linear foot | about $40 to $100 |
| Exterior drain, per linear foot | about $10 to $100 |
| Deep footing drain, per linear foot | about $80 to $100 |
| Drain with sump pump, per linear foot | about $65 to $75 |
National figures, rounded, not quotes. Your price depends on footage, depth, rock, access and discharge.
Sources: Fixr, French drain installation
Questions homeowners ask
Interior or exterior French drain?
Interior drains handle water that reaches the foundation and are usually less disruptive. Exterior curtain or footing drains stop water before it gets there. Hillside homes often benefit from a curtain drain above the house.
How long does a French drain last?
A well-built drain with clean stone and filter fabric can work for decades. Clogging from silt is the main risk, so fabric and cleanouts matter.
How much does a French drain cost per foot?
Fixr lists interior drains at about $40 to $100 per linear foot and exterior drains at about $10 to $100, depending on depth.
Where does the water go?
Interior drains go to a sump pump that pumps it outside. Exterior drains run to a downhill outlet, a dry well or a storm system where allowed. Ask the contractor for the exact plan.
Other services
Basement waterproofing
Finding where water gets in and fixing it for good.
Sump pumps and battery backups
New pits, pump replacements, backups and high-water alarms.
Exterior waterproofing
Excavating, sealing and draining the outside of foundation walls.
Foundation crack repair
Sealing leaking cracks, tie holes and pipe gaps in foundation walls.
Encapsulation and vapor barriers
Sealing crawl spaces and damp basements against ground moisture.
Yard drainage and window wells
Downspouts, regrading, dry wells and window well drains.