Water in your basement often originates well away from your foundation — in your yard, on a neighbor’s slope, or in a low area that concentrates runoff. Exterior drainage systems intercept this water before it ever reaches your foundation. Here is how the main systems work, what they cost, and when each is the right tool.
Surface Drainage vs. Subsurface Drainage
All exterior drainage systems address one of two problems:
- Surface drainage moves water that is pooling or flowing across the ground before it soaks in. Tools: grading, swales, channel drains.
- Subsurface drainage captures water that has already entered the soil and is moving through the ground toward your foundation. Tools: French drains, curtain drains, footing drains.
Exterior French Drain (Perimeter or Yard)
An exterior French drain is a trench filled with gravel and a perforated pipe, installed in the yard to intercept groundwater before it reaches the foundation. Unlike an interior French drain (which manages water that has already entered under the slab), an exterior drain keeps water out of the soil zone around the foundation entirely.
How It Works
- A trench is dug in the yard, upslope from the foundation, 2–4 feet deep
- A perforated pipe (4-inch diameter) is laid in the trench, sloped to drain water away
- The trench is filled with gravel and covered with filter fabric to prevent soil clogging
- Water enters the pipe through the perforations and drains to daylight or a dry well
Cost
- DIY: $10–$30 per linear foot (materials only)
- Contractor-installed: $30–$100 per linear foot
- A 50-foot run: $500–$5,000 depending on depth and complexity
Curtain Drain (Interceptor Drain)
A curtain drain is an exterior French drain installed perpendicular to the natural water flow — it “intercepts” water flowing across the yard from a slope or neighboring property. It is typically installed 10–20 feet uphill from the foundation and runs across the full width of the property to redirect flow around rather than through the yard.
Curtain drains are the right solution when water in your basement is caused by runoff from a sloped yard or hill behind the house — a situation where no amount of interior drainage or foundation waterproofing fixes the root cause.
Cost
- $1,500–$8,000 for a typical residential curtain drain (50–150 linear feet)
- Cost rises significantly if the drain must go through a patio, hardscaping, or tree root zones
Channel Drains (Trench Drains)
Channel drains are linear surface drains — a narrow trench with a grated cover — installed where water concentrates on a hard surface. Common locations: at the base of a driveway that slopes toward the garage, along a patio adjacent to the house, or at the entry to a walkout basement.
- Cost: $30–$100 per linear foot installed; $500–$3,000 for a typical residential installation
- Best for: Hardscaped areas where a French drain can’t be installed
Dry Wells
A dry well is an underground pit filled with gravel (or a perforated plastic chamber) where drainage systems discharge water for slow infiltration into the soil. French drains, curtain drains, and downspout extensions can all outlet to a dry well. They work well in soil with good percolation — less effective in clay-heavy soils where water drains slowly.
- DIY cost: $200–$500 for materials (pre-made plastic dry well chamber)
- Contractor cost: $500–$2,500 depending on size and excavation difficulty
Which System Do You Need?
| Problem Description | Best Solution |
|---|---|
| Water flows across yard from slope above | Curtain drain uphill from foundation |
| Water pools in yard near foundation | Exterior French drain + regrading |
| Driveway channels water toward garage | Channel drain at garage entry |
| Downspouts dump near foundation | Downspout extensions to dry well |
| Water table rises under entire basement | Interior drainage + sump pump system |
| Foundation wall leaks despite good grade | Exterior waterproofing membrane |
Many basements need a combination of exterior drainage to manage surface and near-surface water, plus an interior drainage system to handle any groundwater that still reaches the foundation. See our interior vs. exterior comparison to understand which approach addresses your specific situation.
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