Basement Leakage


Basement, because of its below grade position, is vulnerable to water seepage. Water intrusion is perhaps the single biggest compaint people voice about foundation walls. Statistics tell us that basement leakage is the most common problem found in houses, over 90% of all basements will leak and suffer damage at one time or another. Some evidence of moisture penetration can be found in almost every house. A house with water problems does not necessarily mean it was poorly constructed. Water can appear in even the most well-built home. Not all basement leakage problems are solvable, but, the majority of leakage problems can be solved by directing surface water away from the building, by regrading around the foundation or/and using downspout extension to force rain water to flow away from the house.

During an inspection, home inspector examines basement and crawl spaces, looking for clues that indicate a history of basement leaks and looks closely at the area around the house for conditions that can cause water to accumulate around the foundation. Home inspector recommends preventive measures that the homeowner can take to minimize the chance of water getting to the interior.

Unfortunately, wet basements cannot 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. Visible signs may be concealed by new paint or storage piled against the area. If there has been a dry period before the time of the inspection, signs of past water penetration may not be visible. Even if visible, the clues usually do not give an indication of the severity or frequency.

Even a basement with no seepage problems during a heavy rain does not guaranty the basement will remain permanently dry. A single rain may or may not result in seepage. A heavy rain may not raise the groundwater level sufficiently to cause water to seep through the foundation walls.

Moisture problems are also intermittent. In some houses, water penetration will occur after virtually every rain. In other houses, it will occur only after periods of prolonged rain, and in still others, it will only happen with wind driven rain or during a spring thaw. In most cases however, the resultant damage gives no indication of frequency.

Since virtually all basements leak at some point, the question is probably not, "Will the basement leak?" but, "When and How often?". In this fact sheet, we will try to look at some of most common clues, causes and control for wet basements. Remedies and professional tips to alleviate and possibly eliminate wet basements will be covered.

This section lists some of the clues that may indicate basement dampness. However, the clues are usually inconclusive and can sometimes be misleading. Rust, mold and mildew can be caused by moisture penetration into the basement, but can also be caused condensation forming on foundation walls as hot, humid summer air comes in contact with the cool walls.

Besides, water seepage signs only indicate that water has seeped into the basement in the past. They will not indicate the frequency with which the seepage has occured or the exact extent to which it has occured.

WALL REPAIRS Repairs noted on the interior and exterior which may suggest wet basement problems include patching with bituminous materials, cement parging, or anyone of a myriad of waterproofing products.

EFFLORESCENCE Efflorescence is a whitish mineral deposit often seen on the interior of foundation walls. It forms on basement walls as water migrates through and evaporates, leaving minerals behind. Most people assume that the greater the efflorescence, the more severe the problem. In reality, the drier the air in the basement, the greater the rate of evaporation and hence, the greater the mineral deposits. Therefore, the amount of efflorescence can be increased simply by using a de-humidifier. The presence of efflorescence indicates moisture penetration, although it does not tell a great deal about the severity of the problem or whether the problem is active.

RUST Rusty nails in baseboards or paneling, rusted electrical outlet boxes or rusted metal feet on appliances may indicate wet basement problems.

MOLD, MILDEW, STAINS, DAMAGED FINISHES ETC Other indicators include mold and mildew, water stains, sagging cardboard boxes stored on the floor, crumbling plaster or drywall; lifting floor tiles, rotted or discolored wood at or near floor level, storage on skids or boards raised off the floor, peeling paint, crumbling concrete.

As mentioned previously, clues are usually inconclusive and sometimes be misleading. If there are indications of water seepage, talk with the homeowner about them first and should not engage a contractor to water proof the house immediately upon taking possession. It you do, it could prove to be quite costly. It is possible that whatever it was that caused that past seepage has already been corrected. If the problem was corrected by installing buried drain pipes or by coating the outside surface of the foundation wall, the correction would not be visible.

When a wet basement problem is identified, it should be determined that the source is not from within the house. A leaking plumbing system, water heater, washing machine, or malfunction cooling system, may all be confused with basement leakage. During the summer months, condensation on cold water piping and on cool foundation walls can also be mistaken for leakage.


Most residential foundation walls are dampproofed but not waterproofed. Dampproofing is usually done at the time the building is constructed. An asphalt coating is painted on the exterior of the foundation to prevent seepage. Experience has proven this does not always work.

Literally no conventional residential wall would be sufficient to act as a reverse "swimming pool", that is, to resist water pressure equivalent to a few feet or more. Shrinkdage cracks are common in concrete walls, unsealed tile holes (or improperly sealed) are common in poured concrete walls. Some of the mortar joints in the concrete block and brick foundation wall may have openings.

To waterproof the foundtion wall requires the engineering design of the walls and floor to resist hydrostatic pressure. Homeowners pay hundreds of dollars to water proofing contractors for work that often worsens the water problem and in a surprising number of cases actually collapses foundation walls.


The two most likely sources of water against foundation wall are from surface water, and from roof drains discharging too near the wall, a significant amount of water can easily flow back around the basement wall, filtering down and impregnating the soils adjacent to the foundation. When the ground under and around the house is saturated, water can seep into the basement through cracks and open joints in the foundation. Therefore, The best solution is to intercept the water before it gets to the wall.


One thing that will certainly be true of any basement leak is that there will be exactly as many solutions suggested as solicited.

Most contractors hired to solve wet basement problems are not prepared to bear this responsibility. They do not want to suggest solution that usually work, but sometimes don't, even if those suggestions would result in significant savings for the home owner. Therefore, many contractors offer solutions which reduce their likelihood of receiving call-back. Unfortunately, these solution tend to be the most disruptive and expensive.

On the other hand, if one is willing to invest some time and effort, the majority of leakage problesm can be solved or significantly reduced. Rather than providing a barrier to water penetration, it makes sense to make the water flow away from the building, especially the water that runs off roof surfaces. If it can be collected and discharged away from the house, it will not contribute to basement dampness. Even houses with porous foundation walls and no drainage tiles will not leak if the surface water flows away form the house and is not allowed to saturate the soil around the building.

The best approach to take when considering the correction of water seepage is to immediately correct any obvious problem conditions, such as fautly gutters and downspouts, improper grading, cracks through which water is actively leaking, and so on. During a heavy rain storm, look for the source of water: surface water collecting around the foundation, gutters overflowing etc.

If one cannot afford to experiment (because, for example, the basement is finished or about to be finished), the higher cost but lower risk approach makes sense. However, a less radical and more systematic approach will usually yield a far less expensive solution. Since more than 90% of wet basement problems are caused by surface water (rain or snow) collecting around the building, the surface water issues should be addressed first.

Once the source of the water has been reduced as much as possible, attention should be directed towards localized cracks and holes in foundation walls, which provide little resistance to water penetration. Large scale digging, dampproofing and the installation of drianage tiles should only be contemplated after improving gutters and downspouts, grading, and obvious points of penetration.

The remainder of this section deals with these repairs in order of priority. If the steps are taken systematically, most basement dampness problems can be cured or significantly reduced, relatively inexpensively.


Probably the most common cause of wet basements is improper roof drainage, downspouts that discharge directly to foundation walls.

Eliminating or minimizing the source of the water is very important with respect to keeping any basement dry. The gutters and downspouts must be complete, properly installed and free from leakage or overflowing. Downspouts must be well connected and continuous. The downspouts should either discharge into a waste plumbing system below ground, or above grade at least six feet away from the building, depending on land slope, soil porosity, etc.

Picture: Downspouts that discharge directly to foundation walls can cause wet baseemnt problem

Picture: Use downspout extensions to force rain water to flow away from the house

It is common for downspouts which discharge into an underground system to become blocked with debris or broken below grade level. This can lead to a large concentration of water just outside the foundation wall which almost inevitably results in leakage. Excavating and repairing or replacing this section of piping is expensive. Often, rearranging the downspout (in some case, including those of the next door neighbors) to discharge above grade several feet from the building is a less expensive and equally satisfactory alternative. Where above grade discharge is not practical, the underground drainage system must be repaired.


The other most likely source of water against a basement wall is surface water filtering down to the wall. If a large area drains to a low point at or near the wall, this may well be the source of water problem.

Poor grading is a common problem on houses. The backfill around houses is often not well compacted (for fear of damaging a new foundation walls). Over the first few years, the soil will settle, and the grading may have to be improved.

Regrading the exterior to drain water away from the building rather than toward it is one of the most effective solutions to wet basement problems. Ideally, the ground should slope down away from the house at a rate of one inch per foot for the first six feet. imprerious surfaces like asphalt driveways can slope less, with almost any positive slope being effective.

This work can be expensive where driveway, patios or sidewalks have to be lifted, although in lawn and garden areas, adding some soil is all that is required. Gravel is not a good material to use, as water will flow through this easily. Well compacted soils which force most of the water to run across the surface are preferred.

Localized low areas including basement stairwells, window well may allow water to collect. Drains should be provided in the bottom of these and should be kept clear of debris. If necessary, these openings can be covered to prevent water accumulation. There are clear plastic dome cover available for basement window wells. These do allow light into the basement, although, of course, ventilation is cut off. Grading around window wells is critical.

Some houses have wet basement in the winter only. This occurs because enen in the coldest winter, the soil around the foundation is thawed and porous because of the heat loss from the basement. Everywhere else, the ground is frozen and impermeable. Water from the surrounding area flows down the surface and sinks into the soil around the foundation of houses with poor grading.

Even when basement leakage is not an active problem, good drainage should be ensured during any landscaping or driveway work. Where good grading cannot be achieved, catch basins should be used.

Water should be directed toward the basins which should carry water to a drainage system. Catch basins are prone to clogging and frost heaving. Good maintenance is necessary to ensure a dry basement.

Where drainage cannot be away from the building for six feet or so (because of a neighor's house, for example) the best compromise is a low area between two buildings which directs water along a trough to a point away from both buildings. If this is not possible, a catch basin and drainage system may be necessary.


When a house sits so low to the ground on a flat lot that it is impossible to raise the grade against the foundation, the alternative is to lower the grade in a ring several feet away from the house, thereby creating a gently sloping swale. A swale leads water to a lower area, or it will simply hold the water in a shallow, moatlike ring around, yet away from, the house, where slow percolation and evaporation eventually dispose of it.


Basement wall cracks can sometimes be successfully repaired from the inside. The big appeal of patching cracks inside the basement is that it is inexpensive.

Patching from the outside is more expensive, but more often successful. Covering a patch with a good draining material, such as glass fiber insulation board designed for below grade use, will help protect the patch and keep water away. If the basement is only wet in areas adjacent to obvious cracks, patching may be a practical approach.

Patching cracks is usually only sucessful for minor problems and is only as good as the person who does it. In many cases, the water will simply find another way in. There are invisible cracks, unsealed form tie holes in the poured concrete foundation wall, open (deteriorated) mortar joints in the brick, stone and concrete block foundation walls. They may admit water if other conditions that encourage leakage are present.

It should be understood that patching cracks does not remove the water problem, it only traps the water outside the basement wall and to saturate the soil outside. This greatly increases fluid pressue against the foundation and increases the level of moisture that evaporates into the house. In extreme case, the increased pressure may lead to foundation wall failure. It is better to prevent water accumulation outside the basement, rather than to try to make a boat out of the basement.


When basement leakage cannot be eliminated or minimized by controlling the surface water or by patching, more extensive measures are required. At this point, it is necessary to excavate on the building exterior, to dampproof the outside, and to provide or replace the perimeter drainage tile system.


Because excavating on the exterior is expensive, and almost always leads to disruption of patios, driveways, and landscaping, a less expensive alternative is sometimes employed from the building interior. A roughly ten inch wide strip of the concrete floor is broken up around the inside of the foundation wall. A drainage tile system is installed below the basement floor inside the footings. The water can then be run into a waste sewer system, if gravity permits, or a sump.


Water leakage up through a basement floor slab is usually a result of saturated soil in and around the foundation. This is often accompanied by leakage through the foundation walls, or through the intersection of the foundation wall and the basement floor slab. In severe cases, the hydrostatic pressure can cause the floor slab to heave, although this is more often a result of frost when the house is left unheated during winter.

The corrective actions for basement wall leakage are also appropriate for water penetration through a floor slab. Ideally, the source of the water is eliminated. If this is not possible, the water has to be controlled and diverted to a sump. Original basement floors which were very thin (one inch or less, for example) are sometimes broken up so badly that they are replaced. Gravel fill, four to six inches thick, is usually added before the new slab is poured, and a water-proof membrane (often plastic) may be laid under the new floor. The new floor thickness is ideally three inches, although often the basement headroom in old houses is so restricted that losing another three inches of height is a big sacrifice. As a result, the concrete floor is often thinner.


Blocked or filled weepholes or a lack of proper flashing (Unfortunately, this cannot be assessed during a visual inspection) at the base of the house's exterior brick veneer walls can lead to water accumulating on top of the foundation wall and eventually draining into the basement, instead of to the outside. The water leaks from above the sill plate down to the foundation wall.

Blocked or filled weepholes should be uncloggedand kept clear. Proper flashing should be installed (very costly) if they are missing.


In the very few cases where the problem is ground water rather than surface water, more extensive solutions are required. Normally, houses are not built below the water table. However, the water table may rise intermittently in areas with heavy seasonal rainfall. Changes in neighborhoods as development increases, for example, may lead to changes in the natural water table.

Where the basement floor is below the water table, water constantly pouring into the basement will often be experienced. A drainage tile system and a sophisticated pumping system, perhaps employing dual pumps, is often used. Since the water is constantly present, and pumps are susceptible to either mechanical or electrical failure, a house with this arrangement is always vulnerable to wet basement problems.


Once the problem is identified as exterior water penetration, the corrctive action process would be a step by step approach as follows:

1. Provide or improve gutters and downwpouts, discharge at least six feet from the house, re-arrange the downspout from discharge below to above grade as necessary
2. Re-slope exterior grading with clay-based soil to provide natural drainage of water away from the building
3. Patch any obvious cracks or gaps from the interior
4. From the exterior, excavate and patch the foundations where
leakage is localized. While this is being done, it makes sense
to see whether perimeter drainage tile is in place, if so, to
determine its condition
5. To engage a professional to comment on whether an interior
drainage tile system below the basement floor may be
appropriate, or whether excavation, dampproofing and an outside foundation drainage tile system is appropriate

If chronic flooding is a problem, it may be wise to contact the city and neighbors to see whether the problem is area wide, or specific to one house. Where the problem is a neighborhood situation, the city will often make efforts to improve surface drainage or to control storm water.

People offering quick and easy solutions to wet basement problems are to be approached with some skepticism. Some companies utilize an injection process around the house wherein an expandable mateial such as bentonite clay is used in an effort to fill the voids in the soil around the foundation and prevent water accumulation. Generally speaking, this is not an effective long term solution and, in some cases, there is no noticeable improvement.

On the other hand, people jumping to the conclusion that the solution is always expensive and always requires digging, should also be apporached with some skepticism.

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