Causes of a Leaking Basement – Some Aren’t in the Basement at All


Causes of a Leaking Basement – Some Aren’t in the Basement at All

One of the questions we are most often asked is: ”Why does my basement leak?”

This is usually an easy question for an experienced basement waterproofing professional to answer – provided it isn’t being asked over the phone or at a backyard barbecue.  Give the opportunity to inspect the basement and the area surrounding the house, a pro can diagnose the problem pretty accurately, sometimes with the aid of a garden hose.

As expected, many of the direct causes of a leaking basement are to be found by looking inside the basement itself:

Non-structural wall cracks, the most common cause of leaking in a poured concrete basement, can be found almost anywhere on the wall although they often emanate from window and utility openings;

Cove seepage that is forced into the basement between the floor and wall is easily spotted when dampness or puddles show up in those corners;

Wet or damp walls, particularly those constructed of masonry, are a sure sign that water is seeping through bad mortar joints or porous masonry units;

Water running in trickles (or streams) down a wall indicates that the basement is leaking over the top of the basement wall; and,

Dampness or seepage along cracks in the concrete floor indicates that hydrostatic pressure is forcing water in through the cracks.

All of these causes of a leaking basement are easily spotted and a competent basement waterproofing contractor will be able to repair them permanently.  However, there are a number of factors that occur outside that can cause a leaking basement, several of which can be prevented or repaired by the homeowner; others will require professional assistance.

The Underlying Cause of a Leaking Basement is Water in the Ground

The common thread among all of the exterior causes of a leaking basement is that they all contribute to water in the ground surrounding the home’s foundation.  Saturated soil surrounding a foundation gets that way for one of two reasons: the water table rises from prolonged rain or other factors or soil closer to the surface is inundated with water from rainfall or snowmelt.

When this soil becomes saturated, the soil expands and creates pressure against the foundation walls.  If breaches in the walls already exist, such as any one of the factors discussed earlier, the pressure will force water in.  If not, extended pressure will cause cracks in the wall and cause a leaking basement.

Of course, there’s not much a homeowner or a waterproofing professional can do about rain and snow.  However, there are a number of things that can be done to manage water properly outside the home and to avoid worsening the situation through poor design or lack of maintenance.  All of these are done outside the basement.

Finding and Fixing Exterior Causes of a Leaking Basement

Basement waterproofing professionals use the term “water management” to describe steps that can be taken to properly handle water that occurs outside the home to prevent it from leaking into the basement.  All of these recommended actions are related either directly or indirectly to water management.

Keep Rain Gutters Clean and Flowing – In most parts of the country, houses commonly have rain gutter systems installed along the edges of their roofs.  Typically, only residents of the Southwest and southern California experience little enough rain to safely forego gutters.

Surprisingly, even moderate rains produce a tremendous amount of water.  For example, the average home in the United States has 2,200 – 2,600 square feet of roof surface.  Just one inch of rain falling on a solidly average 2,500 square foot roof will dump 1,500 gallons of water on the roof, enough to fill a 10-foot diameter above-ground pool to a depth of 2.5 feet.  That’s a lot of water!

Without gutters, all of that water would run down the slope of the roof and pour off the edges in sheets, landing on the soil below.  Without some type of management, this water will soak into the soil and create the saturated conditions described above. 

When gutters are clogged, they might as well not be there at all because water will run right over them and end up next to the foundation.  In most situations, cleaning the gutters of leaves, needles and other debris in spring and fall will keep them open and running all year.  This is a job that can be done by many homeowners or fairly inexpensively by a handyman or specialized service.

Extend Downspouts at Least Ten Feet from the Foundation – Another vulnerable point in a home’s water management system is the set of downspouts that carry water collected by the gutters down to the surface.   The gravitational flow of water will usually keep downspouts clean but, if they simply terminate at ground level, they are dumping all of that rain water, now concentrated in only a few spots, onto the soil at the base of the foundation.

That one-inch rainfall will then cause nearly 400 gallons of water to end up at the corners of a home with a typical four-downspout arrangement!

A word of explanation here about why the soil around the foundation is so vulnerable to water: When a home is built, an excavator digs out a large bowl in the earth for the construction of the foundation that typically extends at least 10 feet beyond the foundation’s perimeter.  After the foundation is done, the edges of this bowl are backfilled with soil from the excavation.

Even though the backfilled soil is compacted mechanically, it remains looser than the undisturbed soil around it, leaving it more porous and expansive and more likely to become saturated.  This zone around the foundation is the target of the water management processes discussed here.

So, extending downspouts beyond the 10-foot mark will keep the concentrated discharge from rain on the roof from saturating the vulnerable soil close to the foundation.  There are a number of above-ground extensions available from big box hardware stores but they look messy, have to be removed to mow the lawn and have a tendency to fall off.

An underground downspout extension, installed by a professional, will carry water off to a bubbler pot, dry well, storm sewer or out to daylight.

Make Sure Grading and Landscaping Are Correct – After a house is finished, the contractor will grade the surrounding soil as the basis for a lawn.  Typically, this grade will slope away from the house and run at a gentle angle down to the street.  This will allow rain water and snowmelt to run off the grade and flow to storm sewers or open storm drainage.

If the contractor makes a mistake in the grade or fails to grade at all, a “negative” slope can result where the grade runs toward the house.  This will cause water to flow toward the foundation and increase the saturation of the soil in the 10-foot zone.

Even when the grading is correct, landscapers and DIYers can create a leaking basement by not taking water management into consideration when planting or creating hardscape around the house. 

If a landscape plan includes berms, planting boxes or retaining walls close to the foundation, these additions can retain water and increase saturation.  Properly designed with openings for drainage, landscaping can beautify the home without endangering the basement.

The same applies to hardscape – patios, decks, sidewalks, wing walls and other permanent constriction adjacent to the foundation.  If improperly sloped or insufficiently flashed or sealed, these improvements can cause water to flow toward the foundation, often resulting in seepage over the top of the foundation wall. 

Don’t Ignore the Window Wells – Basement windows bring much-needed light and fresh air into a basement space but they can also be a source of leakage, particularly when the window well is not properly installed or maintained.

Window wells should have drains in the bottom to allow rain and snowmelt to flow out of the well and not turn the basement window into an aquarium.  A clogged or missing drain will cause a leaking basement and should be cleaned, replaced or installed.

Window well covers are essential to keeping out debris that will clog the drain.  Plastic bubbles from the big box hardware store don’t last long and can create a terrarium that encourages the growth of weeds.  The best option is a custom-fitted, steel-reinforced polycarbonate cover that will provide long-lived protection and keep out debris and small animals.

Other than maintaining gutters and landscaping, a homeowner faced with any of these issues outside their foundation will need the advice and services of a basement waterproofing contractor to stop or prevent a leaking basement.  At U.S. Waterproofing, we have as much experience managing water outside the basement as we do in keeping it out once it’s gotten inside.  It’s a part of the comprehensive service we’ve provided to more than 300,000 satisfied customers since our founding in 1957.  Why not ask for our free advice?


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