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Water in Basement: What’s the Cause?


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Water in basements can be an alarming problem, but you’re not alone, it's an issue that many homeowners experience.  Even the most fortified basements are prone to leaking at some point in their life, and this means that there is a good chance you'll need to deal with the problem eventually.

Since there's a number of potential causes of basement leaks, correctly diagnosing the problem is critical if you want to fix it properly. This article will help you navigate a flooded basement.

How to Tell if You Have Water in Your Basement

Basements are prone to flooding. Because water will usually take the path of least resistance, basements can be a magnet to unwanted water since they are the lowest level of a house. This makes being on the lookout for basement flooding warning signs a critical factor in keeping your basement in prime condition. Being well versed in the causes of basement flooding and knowing how to prevent leaks can not only save you from a major headache, it can also save you a lot of time and money.

Sometimes a leak is obvious. A pool of water on the floor is usually a pretty clear sign there is a problem. But other times a leak is a bit more subtle. Here are a few signs that might indicate a leak in your basement.

Signs of a Basement Leak


Efflorescence is a white mineral deposit build-up on materials such as brick, concrete, and clay tiles. It's often powdery and fuzzy and occurs when water seeps through masonry materials. Minerals, such as salts, are carried into and dessolved within the masonry material as the water passes through. When the water evaporates, the minerals are left on the surface.

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Mold and Mildew 

Mold and mildew are commonly found near areas that have been exposed to moisture. Many types of mold will have spores that can be inhaled and cause respiratory issues or trigger allergies. Learn more about mold and mildew here.

Rust Stains 

Rust on metal surfaces, such as iron or steel. The rust is a reddish flaky layer of iron oxide, and it's formed by oxidation. This is evidence of past or present moisture exposure. 

Wet or Rotting Wood

Moisture exposure to wood will cause wood to rot. When the moisture content of the wood goes beyond 30% (the Fiber Saturation Point) wood decay spores will find their way to the surface of the wood. The wood decay spores are in the air, and when temperatures rise, the spores germinate and penetrate the wood.

Stained Floors

Discoloration on floors could be an indication of past or present water absorption due to a leak.

Water Seepage 

Seepage often occurs when water is forcing itself through cracks in the foundation or other porous material. It is not uncommon to see dampness or staining around floor cracks when seeping is occurring.

Drylok Flake

Drylok is a common waterproofing concrete sealer. Since basement foundations are built with porous materials, such as concrete, moisture and water can easily seep through, Drylok is meant to protect against these threats. However, if Drylok is applied to surfaces that have not been properly sealed, the product will bubble and eventually flake off.

Wall Cracks

There are 2 main types of wall cracks that occur in basements. Horizontal cracks are the most serious and are caused by pressure against the walls; and vertical (or diagonal) cracks occure as a foundation ages.

Often concrete will shrink as it cures and a crack will form. However, cracks may also be a sign that the foundation has settled and damage has occurred. Either type of crack can be the cause of water seepage in your basement.

3 Causes of Basement Leaks

There are 3 factors that cause a basement to leak: Hydrostatic pressure, lateral pressure, and window well leakage. Let's take a closer look at each:

Hydrostatic Pressure

Water is always present within the ground, although, sometimes it is quite deep. The water table, which is the level below ground that is saturated with water, differs by location. If you live by a lake, your water table will be much higher than if you live in the desert.

When an area experiences heavy rain or melting snow, water is absorbed into the ground. Once the soil is saturated and can no longer absorb any more water, the water table begins to rise. As the water table rises under your home's foundation, hydrostatic pressure develops. The water must find somewhere to go, and it often goes into your basement.

When an area experiences heavy rain or melting snow, water is absorbed into the ground. Once the soil is saturated and can no longer absorb any more water, the water table begins to rise. As the water table rises under your home's foundation, hydrostatic pressure develops. The water must find somewhere to go, and it often goes into your basement.

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Lateral Pressure

Water is also absorbed into the soil that surrounds your foundation. During normal weather conditions, this does not pose a threat and the soil can usually drain. However, this soil has been excavated and backfilled when your home was built so it's not nearly as compact. Looser soil equals increased absorption within the soil. The more water the soil absorbs, the more the soil will expand.

Soils such as sand, drain relatively quickly and experience little absorption. Others, such as clay, tend to absorb water and expand. Clogged gutters and inadequate downspouts can further complicate the problem and cause a build up of water near the foundation which can result in leaking.

Lateral Pressure occurs when the soil expands and increases the pressure against the foundation. This not only can cause leaks, but it also can damage your foundation.

Window Well Leakage

Leaking that occurs in the window wells is not related to ground water pressure. The purpose of a basement window is to allow light and air into the basement. However, during heavy rains or drainage problems water can collect within the window well.

As the water collects, pressure builds which can cause seepage through cracks or gaps around the window.

A common cause of basement flooding is when water collects inside the window well. As the trapped water builds outside the window it'll increase the pressure on the window and the window seals. Seepage can also occur through the cracks or gaps around the window. However, when enough pressure builds, the window seal will eventually fail creating an even bigger problem.

Types of Basement Leaks and What to Do

Here are types of leakage that can occur in your basement:

Floor Cracks

Water can seep into a basement through cracks in the floor. Since basement floors are typically 2 to 4 inches thick and are in place only to provide a solid base. As the water table rises, hydrostatic pressure increases below the concrete floor and eventually will cause a crack which will ultimately result in seepage when the water table rises.

To resolve this problem, it's necessary to reduce the hydrostatic pressure that builds under the floor. By installing a Drain Tile System you'll be able to direct the ground water to a more suitable location.

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Cove Joint

As hydrostatic pressure increases, water can seep into your basement at the cove joint. The cove joint is where the walls meet the floor. Particularly during times of heavy rain, it's common for water to seep through this joint since water frequently collects under the floor and the foundation walls.

Although you may be tempted to seal the cove joint when you first notice the seepage, it is not typically recommended since you will not be addressing the root of the problem. The hydrostatic pressure will simply continue to build. The best solution is to install a drain tile system below the level of the floor. (See Floor Cracks).

Foundation Walls

Many times water will seep over the top of the wall on the foundation. It's common to see a gap where the foundation wall meets the above ground structure. If the ground surrounding the foundation does not slope away, and water is allowed to pool next to the structure, seepage can occur through this gap.

This problem can be solved by installing an exterior waterproofing barrier. We highly recommend hiring a professional to complete this task.

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Mortar Joints

The mortar joint is the area between concrete blocks or bricks which is filled with mortar. Mortar is a porous material that allows water to seep through. In addition, cracks can form with even a minor foundation movement creating an even larger opportunity. (See Foundation Walls).

Porous Concrete

Concrete generally resists water seepage, however, if not mixed properly, porous spots can form. Over time, these porous spots can be the cause of seepage. (See Foundation Walls).

Wall Cracks

A non-structural wall crack is the most common type of basement leak. Wall cracks that develop in poured concrete is often caused by the foundation settling or by lateral pressure.

Filling the crack with a sealant is generally the best way to solve this problem.

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Window Wells

To repair this problem check outside to see if your window well has a drain. If it does, the drain may simply need to be cleaned or possibly replaced. If there's not a drain you can install one and then direct the water to a drain tile.

The leak could also be related to the window well liner. These liners can create a gap between the window well and the foundation wall if they separate. Many times the liner can be reattached, but if it is clearly damaged you may need to purchase a new one.

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