All About French Drains

A French Drain is basically:

• A trench dug into the ground
• Filled with gravel or rock
• Often containing a perforated pipe
• Wrapped in landscape fabric to keep dirt out

Water naturally flows into the trench, enters the pipe, and is redirected away to a safe discharge point (like a slope, curb, dry well, or storm drain). 

 What problems a French drain solves

✔ Standing water in yards
✔ Basement or crawl-space moisture
✔ Foundation water pressure
✔ Soggy lawns after rain
✔ Water buildup behind retaining walls

Key parts of a French Drain:

• Perforated pipe (usually 4" corrugated or PVC)
• Washed gravel (allows water to flow freely)
• Landscape fabric (prevents clogging)
• Proper slope (gravity does the work—no pumps needed in most cases)
   

Types of French drains

• Surface French drain – catches pooling water in yards
• Subsurface French drain – protects foundations and basements
• Interior French drain – installed inside basements
• Curtain drain – intercepts water moving downhill
  

Why it’s called a “French” drain

It’s named after Henry French, who described the system in the 1800s—not because it came from France.

When a French drain is a good idea

If water:

• Pools more than 24 hours
• Flows toward your house
• Causes mud, erosion, or foundation concerns
  

…a French drain is often the cleanest, long-term fix. Not sure if it is a fit for you? Use the button below to call us!

What a French Drain Really Does (Physics + Practice):

A French drain does not “suck” water away. It gives water an easier path to travel than pushing through compacted soil.

Water always follows:

1. Gravity
2. Least resistance
   

A French drain exploits both.

Step-by-Step: What Happens When It Rains:

1. Water enters the soil: Rain hits the ground and begins infiltrating downward. In clay or compacted soil, this happens slowly, so water builds up and spreads sideways—often toward foundations.

2. The trench becomes the path of least resistance: A French drain trench is filled with washed gravel, which has:

• Large void spaces
• Almost no resistance to water flow
   

Compared to soil, gravel can move water 10–100× faster.

➡️ So water naturally migrates toward the trench.

3. Landscape fabric controls soil migration (critical): The trench is wrapped in non-woven geotextile fabric. Its job:

• Lets water pass
• Stops fine soil
• Prevents clogging and silting
   

Without fabric, dirt fills the gravel voids → drain fails over time.

4. Water collects in the gravel bed

As water reaches the trench:

• It drops into the gravel
• Pressure equalizes
• Hydrostatic force around foundations is reduced
   

This alone can solve many water issues—even before the pipe does anything.

5. Perforated pipe captures and channels water: Inside the gravel sits a perforated pipe (usually 4"). There are Two common orientations:

• Holes down (preferred for longevity)
• Holes at 4 & 8 o’clock (common in manufacturer designs)
   

The pipe does NOT pull water in.
Water falls into it once the gravel fills.

6. Gravity moves water through the pipe: The pipe is installed with a slope:

• Minimum: 1% (⅛" per foot)
• Ideal: 2% (¼" per foot)
   

Gravity causes water to flow continuously, preventing standing water inside the pipe.

7. Water exits at a discharge point: The drain must terminate somewhere safe:

• Daylight on a slope
• Pop-up emitter
• Dry well
• Storm drain connection (where permitted)
   

🚫 If there’s no outlet, it’s not a drain—it’s a soak pit.

Water around foundations creates hydrostatic pressure. That pressure:

• Pushes through concrete pores
• Finds cracks
• Causes basement leaks
• Leads to long-term foundation damage
   

A French drain:

• Lowers the local water table
• Relieves lateral pressure
• Redirects water before it builds force
  

That’s why they’re standard in:

• Retaining walls
• Basements
• Hillside homes
• Flood-prone yards
   

The Soil Factor (This Is Huge)

Different types of soils behave differently with water. This can impact a lot and can make a French Drain necessary.

Clay soil:

• Drains slowly
• Holds water
• French drains are extremely effective
   

Sandy soil:

• Drains quickly
• French drains help redirect flow paths
• Often combined with surface grading
   

Mixed soil (most residential properties):

• French drains shine here
• Especially when paired with proper slope
   

Common Installation Mistakes (Why Drains Fail): Like anything if it isn't done right it won't be effective. There are some common installation mistakes that can be avoided by having a professional install your drain.

❌ No slope
❌ Cheap fabric or none at all
❌ Unwashed gravel (contains fine soil)
❌ Pipe crushed or sagging
❌ No clean-outs
❌ Discharge too close to the house

A bad French drain can trap water instead of moving it leading to more damages. Use the button below to have our experts install your drain.