Interior French Drain Systems for Crawl Spaces
Collect recurring water inside the crawl space and give it a controlled path toward a gravity discharge or sump basin based on the conditions beneath the home.
When Interior Drainage May Make Sense
Interior French drains are typically considered when water repeatedly enters or collects inside the crawl space.
- Water entering along foundation walls
- Recurring standing water after rainfall
- Low areas beneath the home
- Interior perimeter seepage
- Water that needs routing to a sump basin
- Existing drainage that is incomplete or failing
Give Water a Controlled Collection Path
An interior French drain is designed to collect unwanted water from defined areas and route it toward an appropriate discharge point.
In crawl spaces, water can enter along foundation walls, move through saturated soil or collect in low areas beneath the home.
Rather than allowing that water to spread across the crawl space, a drainage system can provide a deliberate route toward gravity discharge or a sump basin.
The layout should be based on the actual water path, elevation and available discharge—not a fixed package.
Conditions We Evaluate
- Where water first becomes visible
- Interior low points
- Foundation-wall seepage
- Soil saturation
- Existing drainage
- Available gravity discharge
- Need for a sump basin and pump
Collect. Route. Discharge.
The system works by creating a controlled path for water beneath or along the interior side of the foundation.
Collection
Water moves into a properly located trench and drainage assembly.
Drainage Pipe
Perforated pipe provides a path for collected water to move through the system.
Slope or Sump
Water moves toward gravity discharge where possible or into a sump basin where pumping is required.
Discharge
Collected water is routed away through the specified discharge system.
An Interior French Drain Is More Than a Pipe in a Trench
The collection area, pipe, aggregate, slope and discharge all need to work together.
Excavated Drainage Trench
Installed along the required perimeter or targeted interior areas based on the water path.
Perforated Drain Pipe
Allows water from the surrounding drainage assembly to enter the system and move toward the outlet.
Drainage Aggregate
Clean stone around the pipe creates open space that allows water to move toward the drain.
Filter Fabric
Used where appropriate to help separate surrounding soil from the drainage aggregate.
Sump Basin
Receives collected water where gravity drainage is not practical.
Solid Discharge Pipe
Carries pumped or gravity-fed water toward the selected discharge location.
A Sump Pump Works Best When the Water Has a Path to the Basin
A sump pump alone cannot collect water from every area beneath a home.
When a French drain is connected to a sump basin, the drain provides the collection path and the pump provides the discharge when gravity drainage is unavailable.
The pump, basin and discharge route should be selected around the drainage system and site conditions.
Learn About Sump Pump Integration →A Typical Sump-Integrated System May Include
- Interior French drain connection
- Sump basin
- Submersible sump pump
- Check valve where specified
- Solid discharge piping
- Selected exterior discharge location
Interior Drainage Is Not the Answer to Every Water Problem
Water Collecting Beneath the Home
Interior French drainage may be appropriate when recurring water enters or collects inside the crawl space and needs a controlled route to discharge.
Water Moving Toward the Foundation
Exterior drainage may make more sense when the main issue is water moving through soil toward the house before it reaches the crawl space.
Water Entering Through a Wall
Foundation-wall water intrusion may require waterproofing in addition to or instead of interior drainage depending on the condition.
Build the Drain Around the Water Path
Evaluate
Identify where water enters and where it collects.
Establish the Route
Determine the required drainage path and discharge point.
Excavate
Create the drainage trench along the specified areas.
Install
Install pipe, aggregate, fabric and sump components where included.
Discharge
Complete the specified gravity or pumped discharge route.
Same Goal. Different Collection Point.
Interior French Drain
Installed inside the crawl-space or foundation perimeter to collect water that has already reached the interior side.
- Interior perimeter drainage
- Low-area drainage
- Sump basin integration
- Can work beneath an encapsulation system
Exterior French Drain
Installed outside the structure or across the property to intercept water before it continues toward the problem area.
- Foundation-side drainage
- Hillside runoff interception
- Yard drainage
- Gravity discharge where elevation allows
Interior Drainage Manages Water — It Does Not Make a Home Floodproof
An interior French drain is designed to collect and redirect water reaching the areas included in the project scope.
It does not prevent plumbing leaks, blocked discharge lines, changing exterior grades, extreme rainfall, neighboring runoff or other future sources of water outside the installed system.
The written project scope identifies the drainage components and areas being addressed.
Address Liquid Water Before Sealing the Crawl Space
Drainage Controls Liquid Water
Interior drainage provides a route for recurring liquid water that enters or collects beneath the home.
If standing water is present, the drainage plan should be considered before the final floor liner is installed.
Encapsulation Controls Vapor & Humidity
Encapsulation addresses ground vapor, wall vapor and air exchange after the required drainage work has been established.
The two systems can work together when the crawl space has both liquid-water and humidity concerns.
View Crawl Space Encapsulation →Interior French Drain FAQ
Does an interior French drain require a sump pump?
Not always. If an appropriate gravity discharge is available, collected water may be able to leave without a pump. Otherwise, a sump basin and pump may be required.
Can you install a French drain before encapsulation?
Yes. When recurring liquid water is present, drainage is commonly addressed before the final encapsulation liner is installed.
Can a sump pump replace a French drain?
A sump pump only removes water that reaches the basin. A drainage system may still be required to collect water from other areas and route it to the basin.
Will an interior French drain stop all future water?
No drainage system can account for every future water source. The system is designed around the conditions and areas included in the written project scope.
Can interior drainage help with standing crawl-space water?
It may be appropriate when standing water repeatedly collects along a defined interior path or low area and can be routed toward discharge.
Do you install exterior French drains too?
Yes. We install both interior and exterior drainage systems, depending on where the water should be intercepted.
Interior French Drain Service Area
Serving homeowners throughout Greenville, Spartanburg, Anderson, Pickens, Greenwood and surrounding Upstate South Carolina communities.
Water Collecting Inside Your Crawl Space?
We can evaluate where the water enters, where it collects and where it can be discharged, then build the interior drainage scope around the actual conditions beneath your home.