Basement   Water  Problems

By Douglas Pencille

Introduction | Diagnosing Water Problems | Typical Problem Areas & Fixes

  Full Depth Basement Diagram



1. Introduction
Basement leakage is one of the most common problems found in houses. While structural damage caused by leakage is very rare, water in the basement can be a major inconvenience, and often causes damage to interior finishes and stored items. In addition, odors caused by mold, mildew, and lack of ventilation are particularly offensive to some people and can even be a source of allergic reaction.

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Unfortunately wet basements cannot always be assessed for their severity, frequency, and inconvenience factor during a one-time visit. There may or may not be clues that indicate a history of basement dampness. Even if visible, the clues do not always give an indication of the severity or frequency.

I have found basement water leakage to be one of the most common defects identified during an inspection.  It can also be one of the most preventable. Basement water leakage is very often the result of improper exterior grading, settled/cracked or otherwise improperly sloped exterior paved surfaces, a lack of proper gutters, etc., and sometimes a combination of more than one of these. Very often, the cure can be as simple as correcting one of the above mentioned deficiencies. 


2. Diagnosing Water Problems
The first step in curing a basement water problem is to determine the source.  Basically, we can divide potential water sources into three categories: 
  • Surface Water
A flow of water that obtains as its basic source, water from run-off, rain, snow, lot drainage, etc., and can be exacerbated by poor soils. This type of water problem is generally restricted to the top four feet of soil.   We think of this as an "external water source".
  • Ground Water
A flow of water that obtains as its basic source, water from high water tables, springs, etc., and can be exacerbated by  poor soils. This type of water problem can extend from the surface, down past the level of the basement floor.  We think of this as an "external water source".
  • Other Water
This category includes all other potential sources, whether they are inside or outside (i.e. condensation due to temperature differences, inside plumbing leakage, outside plumbing leakage, etc.).  This can be both an "external water source", as well as an "internal water source".
Start by asking yourself, "When does the leakage manifest itself?"  Does it show up immediately after only heavy rains?. . .or, every time it rains?  Is the leakage usually confined to one specific area?. . .and if so, can I associate an external source with this area (such as a window well, a poorly sloped driveway, etc.)?

It is very common to misdiagnose a basement leakage problem as being from an "external water source" (surface water or ground water), while it is actual coming from the "other water" category.  A leaking water line inside a basement wall, sewer backup through a floor drain causing basement flooding, condensation on water pipes & walls during summer months, all can make a localized area very wet.  This can easily be mistaken for basement leakage.

Look for some of the signs that indicate leakage. They can assist in indicating what type of problem you are having and can also help in locating the source of leakage.  Some typical indicators are:
  • Dampness/Staining On Carpets - Can indicate past leakage. Identify when and in which locations in the basement, this occurs
  • Efflorescence - A whitish mineral deposit that many times is visible on masonry surfaces.  Usually the result of water passing through the wall.
  • Mold/Mildew - Usually located on or near, an area that has seen prolonged moisture, giving the mold a chance to grow.  Often associated with an unpleasant odor.
  • Rust Stains - Sometimes seen on concrete floors and carpet, usually due to rusted metal feet on furniture. Rusty nails on baseboards, electrical boxes, etc., all indicate evidence of past moisture.
  • Stained/Darkened Wood - Can indicate past water absorption, due to leakage.
  • Dampness/Staining Around Floor Cracks - Can indicate that water is forcing itself up though the cracks, due to pressure, water table, etc.
  • Water Bugs - Look for evidence of small insects along the baseboards, behind sofas, in corners, etc.  Some types of insects gravitate towards areas of moisture.  
Once you have determined the source of the leakage, you can go about taking steps to repair the problem.


3. Some Typical Problem Areas & Fixes
Listed below, are some of the more common causes for basement water problems.  Please refer to the "Full Depth Basement" diagram:
  • Poor exterior grading along the perimeter of the foundation walls is likely the number one cause of leaky basements.  Common sense tells us that we want surface water to flow "away" from a house, not to collect and pool adjacent to the foundation walls. A good "rule of thumb" is a 1-to-1 relationship in slope. In other words, at least 6-8 inches of slope away from the foundation walls, extending for the first 6-8 feet.  (items #1 and #2 in diagram)
  • Lack of adequate gutters can force water run-off from the roof, directly onto the loose filled area of the "excavation ring".  Ensure that your gutter extensions are long enough, so they extend past the excavation ring. Replace any leaking or rusted gutters. (Item #2 in diagram)
  • Poor grading inside window wells as well as a lack of window well covers, can greatly contribute to basement leakage.
  • Plant and shrub overgrowth, especially when very close to the foundation walls, can allow for water to penetrate next to the house, by following the root systems.  
  • Landscape edging that is too high and doesn't allow for water to flow over it can act as a dam, restricting water from flowing away from the house.
  • Patch or fill any cracks in foundation walls.  Smaller cracks can be filled with caulk or mortar. Larger cracks, or cracks that extend well below the surface, may require special repairs (epoxy, rubber membrane, etc.), and a specialist should be consulted.
  • Cracked or poorly sloped paved surfaces that are adjacent to the house can greatly contribute to water intrusion, because they shed water so fast.   Any open gaps in driveways, patio slabs, etc., adjacent to foundation walls should be caulked.
  • If the water level inside the sump basket is up onto (or close to) the entry drain tile lines (see item #5), it can back up around the house, inside the lines, creating a leakage problem. When water levels are this high, it's time to install a pump.
  • Patch / fill open cracks in basement floors with epoxy, to prevent water from being forced up through them.
  • Always operate a dehumidifier in the summer months.  While central air conditioning will provide some dehumidification, there is no substitute for a stand-alone unit.
  • Wrap pipes with insulation. Some water lines are more prone to condensation than others, and consideration should be given to placing insulation wrap on them, to minimize the potential for condensation & resulting dripping.
For more difficult basement leakage issues, there are other water control measures that can be undertaken.  Some of these include installation of new foundation waterproofing, new tile lines, an interior perimeter drain system (often called a "beaver system"), etc.   These measures can be intrusive and very expensive.  They should be considered only if all other options have been exhausted.  Check out our Industry Links page for contacts in this area.


Typical Configuration For A Full Depth Basement Using Hollow-Core Masonry Foundation Walls

Cut-away diagram showing a full-depth
basement with some of the typical
components and systems that are
designed to protect against base-
ment water leakage.


The following information details what is happening in Figure 1 above:

  1. Excavated Area – The area that is back-filled after foundation walls are constructed; often referred to as the "excavation ring". This is the area of loose soil around the perimeter of any building with a basement. Loose fill is more susceptible to water intrusion than undisturbed soil. It is very important to maintain slope away from the foundations, through- out this excavated area. One should also ensure that gutter downspouts are long enough that they don’t discharge into this area.
  2. Soil Settlement – Over time, the loose back-filled area in the "excavation ring" can settle, causing water to flow towards the foundation walls.
  3. Soil Saturation/Hydrostatic Pressure – Water will have a tendency to flow through & saturate loose fill more readily than undisturbed virgin soil. The soil in the excavation ring can become saturated very quickly, exerting great horizontal charges on the walls, as well as forcing water into the block. Professionally applied foundation waterproofing/damp-proofing  will help reduce chances of water entering into the foundation walls above the footing/drain tile line.
  4. Drain Tile System – Most of the water should be captured by the exterior drain tile and funneled away from the house. What water remains should be captured by the interior drain tile system which empties into a sump basket.
  5. Sump Basket & Pump – Water is collected in a sump basket until it reaches a level that causes the sump pump to activate and pump the water out through a discharge line. 
  6. Sump Basket Discharge – Most municipalities do not allow sump basket water to discharge into the sanitary sewer. Sump basket water should be discharged outside.
  7. Discharge Line – The exterior discharge line should be long enough to extend past the excavation ring, so that the discharged water doesn’t seep back down and get recycled.



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