BASEMENT FRENCH DRAINS (PRESSURE RELIEF SYSTEMS)

If you are seeing water in your basement, a French drain – also called a Pressure Relief System (PRS) – is one of the most effective ways to deal with hydrostatic pressure and keep your basement dry. Instead of trying to stop water at the surface, a basement French drain system collects water at the base of your foundation and moves it safely to a sump pump for discharge.

At Main Line Waterproofing, we install interior French drains every day for homeowners dealing with leaks, damp floors, and seeping walls. Done right, a French drain installation protects your foundation, eliminates moisture, and gives you a usable, comfortable basement for the long term.

Seeing water around your basement walls or floor? Contact Main Line Waterproofing for a free assessment and expert French Drain solutions.

What Is a French Drain and What Does It Do?

A French drain is a hidden drainage system installed below your basement floor along the perimeter (or partial perimeter) of the foundation. When water builds up around your home, it creates hydrostatic pressure that pushes through cracks, joints, and porous concrete. 

A properly designed French drain:

• Relieves hydrostatic pressure under the floor and against the walls
• Collects groundwater before it can force its way inside
• Channels that water into a sump pump basin
• Helps prevent leaks, cracks, and long-term structural damage

The result is simple: less stress on your foundation and a much drier basement.

How Our Interior French Drain Installation Works

Every home is different, but our interior French drain process follows a clear, time-tested sequence:

1. Inspection and Plan

We start with a free basement evaluation where we look at:

• Where water is entering
• How your current drainage and sump pump are set up
• The condition of your foundation walls and floor
• Any existing systems that may need repair or replacement

From there, we design a French drain basement system tailored to your specific problem areas.

2. Cutting and Excavating the Trench

Our crew carefully breaks up a strip of concrete along the inside perimeter of your basement floor. In some cases, we only treat the side or corner where the water problem is worst, rather than the full perimeter.

Under that strip, we dig a trench down to the footing. This is where the water naturally wants to collect, so it is the ideal place to install a pressure relief system.

3. Installing the Drain Pipe and Stone

Inside the trench we:

• Line the trench with filter fabric to help prevent clogging from fine soils
• Install a 4-inch perforated pipe that allows groundwater to flow into the system
• Surround the pipe with clean, washed stone to promote free drainage

This creates the actual French drain, which quietly collects and carries water before it reaches your basement floor.

4. Adding the Drainage Board

Next, we install a drainage board against the basement wall and over the footing. Any moisture that seeps through the wall is directed down into the French drain, instead of bleeding out onto the floor or into finished walls and insulation.

5. Connecting to the Sump Pump

The French drain piping is pitched so that all the water flows into a sump pump basin. Your sump pump then discharges the water away from the foundation. If needed, we can also:

• Upgrade or replace an undersized or failing sump pump
• Add a backup pump or battery system
• Extend or improve the discharge line to keep water away from the house

6. Patching the Floor

Once everything is installed and tested, we backfill the trench with stone and pour new concrete over top. When we are done, your basement floor is solid and level again, with the French drain system working out of sight under the surface.

Common Signs You May Need a French Drain

Not sure if a French drain is the right solution? Here are some common warning signs that point to hydrostatic pressure and a need for an interior drainage system:

• Persistent damp spots or puddles on the basement floor
• Water seeping in where the floor meets the wall
• Cracks in basement walls or the slab that let water in
• Musty odors, visible mold, or mildew growth
• Paint bubbling, peeling, or white powdery staining (efflorescence) on walls
• A sump pump that runs constantly or still cannot keep up during storms

If you recognize a few of these, a basement French drain may be the most reliable way to control water and protect your foundation.

Interior vs. Exterior French Drains

French drains can be installed inside or outside the foundation.

• Interior French drains (this page) sit under the basement floor, along the footing. They are ideal when water is coming through walls, the cove joint (where wall meets floor), or up through the slab.
• Exterior French drains are installed outside along the foundation wall and are more commonly used when there are major grading, gutter, or surface water issues around the home.

During your inspection, we will let you know whether an interior PRS system, an exterior French drain, or a combination of solutions makes the most sense for your situation. If an exterior system is a better fit, we will walk you through that option as well.

Why Homeowners Choose Main Line Waterproofing for French Drains

There is no shortage of waterproofing companies and French drain contractors out there. Here is what sets Main Line Waterproofing apart:

• More than 35 years of experience solving basement water problems in the Greater Philadelphia region
• No high-pressure sales – we evaluate your specific needs, explain options, and give you a clear, detailed estimate
• Owner-supervised crews – our trained team handles the work, not random subcontractors
• Custom solutions – we do not push one “system” on every home; we design drainage around your foundation, soil, and water issues
• Honest, long-term thinking – our goal is not just to fix today’s puddle, but to reduce future risk to your home

From simple French drain repairs to full-perimeter French drain installation with multiple pumps, we scale the solution to your needs and your budget.

Maintenance and Long-Term Performance

A French drain system is designed for long-term performance with minimal day-to-day upkeep, but there are a few basics that help it last:

• Keep gutters and downspouts clear and draining away from the foundation
• Make sure discharge lines stay open and do not freeze or clog
• Test your sump pump periodically, especially before heavy rain seasons
• Call us if you notice new cracks, damp spots, or changes in how often your pump runs

If you already have a French drain that is not working properly, we can inspect it and recommend repair, cleaning, or replacement options.

Get a Free Basement French Drain Evaluation

If you are tired of dealing with a wet, musty basement, you do not have to guess at the solution. We will:

• Inspect your basement and foundation
• Identify where the water is really coming from
• Explain whether a French drain, sump pump upgrade, or another basement waterproofing service is the best fit
• Provide a clear, written estimate with no pressure and no surprise add-ons

Call 610-642-4444 or request a free inspection today to find out if a basement French drain is the right way to protect your home and reclaim your basement.