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Hydrostatic Pressure and Why a Basement Leaks

Mar 28, 2012 • By Matthew Stock with Barry Schilling.

Hydrostatic Pressure and Why a Basement Leaks

When we first became homeowners, we knew that certain pressures came with the job – paying the mortgage, fixing things that break or replacing things that really break.  We probably didn’t think much about something called hydrostatic pressure, but many of us are dealing with its consequences.

Hydrostatic pressure is one of those fancy terms a basement waterproofing contractor may use to describe the source of water coming up through your basement floor.  It sounds serious – and it is!

So, what is hydrostatic pressure, where does it come from, and how do you stop the rising water it produces from seeping onto your basement floor?

What’s a Water Table?

Any discussion of hydrostatic pressure must start with some information on the water table. Simply put, the water table isn’t furniture but the level of the water in the ground on which your home sits.  There are a number of factors that affect the water table, with the most common being proximity to large bodies of water.  Even if you live miles from the lakeshore, Lake Michigan keeps the water table high in the Northeastern Illinois, Wisconsin, and Northwestern Indiana areas.

The frequency and intensity of rains also play a large role in determining the water table.  And, if your home is built on the dense clay soil that is very common in the Chicago area, you are more prone to higher water levels due to clay’s lack of absorption.

A quick story on water tables: A contractor we know put an addition on his home in Lake County 10 years ago.  He dug the basement for the addition one foot lower than the existing foundation and, no surprise, hit the water table.  Mistakenly thinking it was no big deal, he continued with his project.  Now, the two sump pumps in the addition run nonstop in the middle of winter, moving more than 135 GPM (gallons per minute) all the time.  The moral of this story:  Beware the water table!

Hydrostatic Pressure on the Rise

So, we have this body of water in the ground…and now it’s raining.  Every day.  For a week.  As the rain seeps into the ground, the water table rises because the ground is unable to soak up all the water.  This rising water table creates hydrostatic pressure against your foundation and the pressurized water will find every little crack, chink and hole in your foundation walls and floor and make its way into your basement.

Time to Face the Facts

The fact that the basement waterproofing contractor is talking to you about hydrostatic pressure is a cause for concern because you probably have water coming up through the basement floor.  So, what’s the solution?  Unless the water is the result of a failed sump pump, it’s most likely that your home’s drain tiles have failed and will have to be repaired or replaced.

A properly functioning drain tile system will capture rising water and carry it off before it can penetrate your basement.  Drain tiles can be installed inside or outside your foundation and a detailed discussion of how they work can be found in our recent blog Interior Drain Tile vs. Exterior Drain Tile - Which System is Better

We’re sure you’d agree that the normal pressures of home ownership are enough these days without adding the hydrostatic kind.  Fortunately, we have 55 years of experience dealing with hydrostatic pressure.  Give us a call or visit us at

Tags: foundation waterproofing, basement waterproofing facts, french drain, drain tile, interior drain tile, drain tile in basement, exterior drain tile, most common problems, hydrostatic pressure

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