What Every Homeowner Needs to Know About Wet Basements and Seepage


What Every Homeowner Needs to Know About Wet Basements and Seepage

Owning a home may be the American Dream but for an inexperienced homeowner it can often turn out to be a bit of a nightmare.

Houses don’t come with owner’s manuals.  There’s no “Homeowning for Dummies” book (although we may have just given them an idea.)  Short of a nearby parent, friendly and capable neighbor or a well-timed episode of a DIY TV show, new homeowners are pretty much on their own when it comes to taking care of their largest investment.

In our decades of fixing and preventing wet basements we’ve learned that one thing that particularly freaks out inexperienced homeowners is finding water in their basement.  Visions of major damage (and major costs to repair it) sometimes obscure a clear picture of exactly what’s wrong and prevent the homeowner from putting the problem in the proper perspective.

So, for homeowners both new and of long tenure, we thought we’d provide a look at how wet basements occur.

Wet Basements and Seepage – A Primer

Let’s start this discussion with some good news.  A wet basement, although definitely not a problem to be ignored, is generally not something that will destroy a home.  Infiltration of water on its own won’t necessarily damage a foundation, although it is sometimes a sign that such damage already exists.

The damage that occurs from water seepage is most profoundly felt in a finished basement where flooring, furniture and drywall can be damaged or destroyed by water.  Even in an unfinished basement, water can damage or destroy stored goods, laundry appliances or tools.

Even if none of this occurs, there are several good reasons not to ignore a seepage problem.  Allowing water to remain present in the basement can increase the level of humidity in the entire home, causing unpleasant conditions and making HVAC systems run longer.  More importantly, water in the basement can be a catalyst for the growth of mold, which can create serious health problems for the home’s residents.

Having established that water seepage is a problem for any basement, the next question to consider is where does it come from?  The answer is brief but not particularly simple – it comes from water in the ground.  Soil that either underlies or surrounds the foundation absorbs a certain amount of water, the quantity of which depends on the soil’s composition, amount of rain or snowfall and topographic condition around the home including the grade of the surrounding yard and the presence of outside elements such as decks and patios and the existence of certain landscaping features such as planting boxes and berms.

Of course, there is also water that is present in the ground regardless of rainfall or any of their factors noted above.  Known as the water table, this subsurface water exists virtually everywhere, sometimes close to the surface, sometimes far below.  The level of this water is determined by factors like climate and proximity to large bodies of water; it remains relatively stable, changing only in times of drought or extremely heavy rain.

One thing is true about any of this water – it creates pressure against foundation walls and basement floors.  It is this pressure that can find or create openings and force water into the basement.

One opening that already exists and is a common source of water entering the basement is one that was created during construction of the home.  Foundation walls, whether they are constructed of masonry or poured concrete, sit on footings, which are wide slabs of poured concrete that describe the perimeter of the foundation.  Because there is no bond between the wall and the footing, an infinitesimal gap exists there; a similar gap exists between the footing, wall and basement floor.

When hydrostatic pressure builds below the basement floor, the water that creates it can be forced through this gap and into the basement, a condition known as cove seepage.  If the basement floor has cracks in it, hydrostatic pressure can also push water through them to create puddles on the basement floor.

Pressure created by oversaturated soil is also common around the foundation, not just under it. When the soil surrounding foundation walls expands from absorbing too much water, it presses laterally against the foundation and, when it becomes strong enough, can actually cause cracks in a poured concrete foundation wall and can crack mortar joints in masonry walls.

Of course, once these cracks occur, the pressure forces water through them into the basement, which appears as wet stains on the wall or a drizzle running down it.  This is the most common source of seepage in a poured concrete foundation.

Other factors can be culprits in causing a wet basement as well.  For example, a normal grade around a house is pitched away from the building so that rain water and snowmelt flow down the incline instead of back toward the house.  If the grade has been done improperly causing water to flow back it can enter the basement over the top of the foundation wall where it meets the aboveground structure.

Also, if landscaping or other exterior improvements are constructed in such a way that they hold water near the foundation, water can enter the basement the same way.  These typically include planting boxes and beds, berms and hardscape like decks and patios.

Although not as common as the other points of entry, water can also enter a basement through the foundation wall itself without a visible crack or opening.  Concrete walls can develop porous patches that usually result from an error or omission when the concrete is poured – an air pocket or dry spot caused by insufficient mixing.  Masonry walls are held together with mortar that can deteriorate over time and allow water to seep through.

Beyond the common entry points for water into a basement, homeowners should be aware of conditions that can make the problem worse or even create one where none existed before.

The most common problem has to do with the management of rain water outside the home.  To understand why this is important, it helps to know something about the way the house was constructed.

The first step in building a house is an excavation to accommodate the foundation.  The excavator digs out of the earth what is essentially a large bowl where the footings will be poured and the foundation walls built.  When these are complete, the soil is backfilled around the foundation.

Before the digging began, the soil was solidly compacted -- the foundation rests on this type of soil.  The backfill, however, is much looser than the undisturbed soil and creates a zone about ten feet wide around the house that is much more susceptible to absorption of water than the soil around it.  Water ending up in this zone is more likely to cause basement seepage.

For example, except for arid areas in the west and southwest, most homes in the United States are fitted with a gutter system along the eaves of their roofs.  These gutters catch rain water as it runs down the slope of the roof and carry it off to downspouts.

If the gutter becomes clogged with leaves, pine needles or other debris, it can no longer catch and hold the water.  When this occurs, the water will sheet off the edge of the roof and fall to the ground right next to the foundation, soaking into the soil in the backfill zone and creating the potential for basement seepage as mentioned above.

If this doesn’t sound like a big problem, consider that only one inch of rainfall will dump approximately 1500 gallons of water on the average-sized roof.  That’s a lot of water to end up in the basement!

Of course, the performance of the gutter system is only as good as the downspouts they empty into.  Downspouts are not as susceptible to clogging because the water flowing through them usually cleans them out but they are subject to their own issues.

All too frequently, downspouts just end with a vertical tube without any sort of extension to carry water away from the house.  In this case, all the rain water collected by the gutters will be deposited in a few spots, typically four or five, around corners of the house and right next to the foundation.

Next stop? The basement.

There are a few other circumstances that may lead to water in the basement but these are by far the most common.  In a future article, we’ll discuss the ways these seepage problems can be detected and repaired.

Whether you are a first-time homeowner or a veteran, you’ll need professional advice and assistance when seepage occurs in your basement.  At U.S. Waterproofing we’ve been advising homeowners on how to keep their basements dry and healthy since our founding in 1957.  During that time, we’ve helped more than 300,000 satisfied customers with their basements and have earned a reputation as the leader in basement waterproofing and foundation repair in Chicago and surrounding areas.  Why not ask for our free advice?


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