Many “how-to” magazines run articles touting miracle products that stop water from permeating through foundations or basement walls and floors. While some products may be effective at mitigating water migration through cracks or flaws in a wall, blocking groundwater can be as tough as keeping water from leaking through split seams of a wooden boat. So long as any part of the boat is in the water, a certain amount of water is bound to find its way inside.

Never wait until water enters the basement or permeates the foundation before treating the root cause. The resulting dampness is both distasteful and potentially dangerous, even if there is no noticeable standing water. There are four ways that moisture can permeate foundations or enter and collect in basements:

High groundwater table

Surface (rain) water leaking through openings or flaws in the walls

Condensation

Broken plumbing and/or irrigation runoff

Wet basements are a very common problem, particularly in low-lying areas or mountains where high water tables are common. This means that the ground water level has risen up to its high point for the year due to melting snow, spring rains, lack of water pickup by the trees and plants, and the absence of sun to dry the ground during the winter.

Some soils such as clay bind water tightly, keeping the water table high for extended periods. Porous soils including sands and gravels pass water quickly, yet often have high springtime water tables, especially in low areas due to excess springtime runoff. Unfortunately, many homes are built with inadequate protection from groundwater, even though site conditions may be well suited for the proper installation of a simple and cost-effective drainage system.

Once a water problem is discovered after a house is built, it is very difficult and expensive to remedy. If left unchecked, structural and health-related problems may persist. Excessive moisture not only results in a musty smell or damage to carpet and wood flooring materials, but it promotes growth of mold spores, which can result in asthmatic symptoms in many people. For this reason, the use of vapor barriers under slabs as well as other drainage techniques are essential to keeping your home dry year-round.

To help illustrate the high groundwater problem, imagine a 12″-high pile of sand in the middle of your bathtub — with six inches of water in the tub around it. If you were to dig a six-inch-deep hole in the sand, you would find water at the bottom of the hole. By adding more water to the tub, the water level in the hole would rise as the surrounding water reached equilibrium due to hydrostatic pressure. This simulates the effect of a higher water table acting on a foundation. Now, inserting a watertight box into the hole would cause it to float. If there were holes in the box, water would seep inside. In this analogy, the box is the basement or foundation, and the tub water is groundwater.

Wrong Culprit Years ago I did a job for a homeowner who insisted that her basement became wet only after a rainstorm. After lots of digging and waterproofing, (and continued water in the basement) I was left with a serious question about the real source of the water. Finally I started checking the house plumbing and discovered a leak in the water heater! I’ve learned to more be suspicious.

Keeping Water Out

Ironically, making residential basements absolutely watertight can lead to other problems if not properly engineered. For example, basements of many commercial buildings in highly developed areas are built watertight. However, their construction costs are extremely high compared to typical residential basements because their foundations and floor systems are built to far more stringent specifications. This is not only to keep water out, but to keep the high pressure of outside water from causing structural damage. Consider this real-life situation that occurred a few years ago: During one extremely rainy night, a family awakened to a strange sound coming from their basement. Apparently, excess rainwater had saturated the ground around their home given its location in the lowest section of their development. The extreme pressure from the accumulated ground water actually buckled up the basement floor, causing the soil from under the floor to erupt six feet, covering their washer and dryer. The sudden soil displacement undermined the overall foundation, causing one of the walls to fall over a foot. The house was abandoned for massive structural repairs. Although this is an extreme example, it demonstrates the powerfully destructive force of water. This foundation was built in a manner similar to many residential basements. Yet, by allowing the groundwater pressure to rise without relief, failure resulted in the weakest part of the structure which, in this case, happened to be the concrete floor. Ironically, if homes were absolutely watertight, they might even float like the box in the bathtub, resulting in an unstable structure. However, many homes have sump pumps to discharge out any water that might leak in which could otherwise damage the basement. Fortunately, as water is pumped out of the basement, the water table around the house is lowered, (like pulling the plug on the bathtub drain) relieving the “hydrostatic” pressure. This is why floating houses or erupting floors are rare.

One effective way to check the water table near a house which has a dug well is to uncover the well and measure the depth from the ground surface down to the water. Compare this depth to that of the basement floor below grade and the difference equals the depth to which the basement would flood if the water were not removed. Even if the house is located on sloping terrain, the water table remains approximately the same distance down from place to place as groundwater tends to follow the contour of the surface.

Perimeter Drains

In many situations, particularly in mountainous regions where the land is seldom flat, it is possible to drain water away from most foundations and basements by gravity rather than by pumping. The traditional method specifies a perimeter drain around the outside of a building during its construction. The drain outlet slopes downhill away from the house until it reaches the surface of the ground where it can freely discharge by gravity flow. The advantage of this method over pumping water out of a sump is that it lowers the water table around the house, preventing water from ever reaching the cellar in the first place.

In many instances where experts have been asked to troubleshoot wet basement problems, a common finding is drain pipes that were installed above the foundation footing, which allows water to rise to the level of the floor (Figure A, level Y). If the builder made the additional mistake of installing the drain pipe with the weep holes facing up, then the level of water has to rise to the top of the pipe (level X) before the pipe can pick up any water. Other times there is little or no porous bedding material and pipe inlet holes can become plugged. Another problem occurs with large bedding stone. Migration of the original soil into the bedding plugs up the stone, leading to failure. Often a combination of problems may coexist. Most contractors use 1 1/2″ crushed stone around the outside of PVC or thinwall perforated septic system pipe which has 1/2″ or 5/8″ holes every few inches. Usually this is entirely satisfactory, though in some cases capillary action (wicking) within the soil can make the basement floor damp even though it is a few inches above the artificially lowered water table.

Due to the severe conditions encountered when building a home several years ago, the following example illustrates an improved method. Just as sitework started, the property was deluged with rain. The rain aggravated an already difficult groundwater situation, threatening postponement of construction. However, with patience (and a good pair of rubber boots), perimeter drains were installed four feet outside of where the house was to be located. Within days of installing the drains, excavation for the basement was able to proceed as if it were a dry summer. The home is built into the ground about six feet deep on a gently sloping hill. Several years have since passed and the home has never been bothered by moisture in the basement. This is in spite of the original springtime water table just two feet below the surface of the ground. This same procedure is excellent for drying out existing wet basements where conditions permit.

Ensuring Effective Drainage

The first consideration is setting the drain pipe deep enough to lower the water table well below the floor in order to reduce the effects of capillary action (wicking). Another way to reduce this effect — generally limited to new construction — is to install a layer of crushed stone entirely under the basement floor. Water cannot “wick” through this coarse aggregate. Although this is more costly, it is good insurance for a dry basement. Alternatively, installing the drain pipe a little lower may be a very cost-effective alternative, assuming there is sufficient side hill grade to ensure gravity discharge well away from the structure.

For new construction and retrofit situations, place the drain pipe a foot or more lower than the footing whenever possible and far enough away to avoid undermining the foundation. Generally 2′ to 4′ or even more is necessary to protect landscaping or porches and similar structures. In retrofit situations, installing a drain on the upgrade side of the house can yield a significant improvement, as it is usually only necessary to intercept water moving through the ground toward the house to eliminate the moisture problem. This type of drain is considered a “curtain drain” rather than a footing or perimeter drain, especially if it is several feet from the house. Its job is to lower the water table downgrade in order to protect the house. The curtain drain method is an important consideration particularly for retrofit installations as it can reduce site disruption and the resulting cost of excavation.

Properly installed perimeter drains create an “island” out of the house site by lowering the water table completely around the house. They keep water from entering under the footings and, in my experience, provide the surest protection against any type of dampness in a basement resulting from groundwater. There are some situations where perimeter drains are not necessary, however. A thorough knowledge of the site, or an exceptionally low water table indication from a septic system test pit, can provide such a determination. If you happen to be one of those folks already blessed with an unwanted indoor swimming pool each Spring, whether in a new or existing house, rest assured that there usually is something that can be done. However, since soil conditions vary so greatly, it is wise to consider your circumstances carefully before deciding on a course of action.

Leaks in Foundation Walls

Another condition that can sometimes appear to be high ground water leaking in may simply be surface water entering over or through the foundation at bulkheads or window openings, seams between walls, and/or, flaws in the foundation. Poor surface grading can direct water toward the lip of a bulkhead or towards basement windows where it can spill over into the basement. By not paying attention during heavy rains, a homeowner can sometimes end up blaming the wrong culprit.

Surface water leakage

Surface water leakage is reasonably easy to locate once you get on track. The solution often involves regrading to drain water away from the foundation. In the case of foundation windows, however, it is not always possible to shed water away since the bottom of the windows are often too far below the adjacent ground, requiring the installation of window wells. These often consist of corrugated galvanized steel half circles but can also be made of pressure treated wood or masonry. The goal is to make the top of the window well high enough to be able to slope the surrounding ground surface away from the house. A problem arises when the window well is directly below the roof drip, especially in cold, wet climates where rain gutters are seldom used (because snow and ice fills them, making them useless, or ripping them from the building!) The solution is either to cover the window well with a clear plastic dome which also keeps out leaves and critters or to create a mini-drywell under the window well to allow rainwater to soak away into the ground before it can rise up and find its way through the window. This leads to another issue: porosity or flaws in the wall itself. If a foundation wall is totally watertight there is little problem with letting water run down against it all the way to the perimeter drain. If the wall has had adequate damp-proofing and/or the water drains quickly through the soil, there is little to be concerned about. The problem is that many foundations are have defects and hairline cracks which allow water infiltration.

Sources of Leaks in Foundation Walls

Concrete block foundations often crack in the grout joint between blocks. Even poured concrete or ICF walls can develop shrinkage or settling cracks in addition to water channels from anchor bolts and form ties. Honeycombing due to improper vibration and consolidation is another source of leakage, wherein the concrete aggregate became separated leaving voids in the wall. In addition, poured walls often have seams between different stages of the pour. Another problem exists with many of the older foundations that are constructed of various sizes and shapes of cut granite and round fieldstone. With or without mortar between, these foundations typically exhibit numerous passages for water to follow. Water can enter walls around utility penetrations such as sewer, water, gas or electrical conduits. There are several instances where I’ve been engaged to dig around existing buildings and to waterproof walls and/or install drainage systems only to discover that the actual problems were unrelated to groundwater.

Condensation

The effects of condensation can be as devastating to a home as water leakage, causing rot, mold, mildew and generally disgusting and, possibly unsafe conditions. (I have seen mushrooms growing inside on occasion). Since so many local dwellings in remote areas are vacation homes, many are lived in only a part of the time. This can mean inadequate ventilation (as houses are closed up much of the time) which is often aggravated by colder-than-normal internal temperatures. Many of these homes are only heated to just above freezing during much of the winter, if at all. When folks arrive for the summer, they open the house, letting in warm, humid air that condenses its moisture against cool basement surfaces. Perhaps the best solution for this is to have the house opened earlier in the springtime, allowing the basement temperature to equalize. Air conditioning can also help, but at least one basement drainage expert warns that dehumidifiers may actually cause more damage to basements. Written by Russell H. Lanoie, Rural Home Technology at www.ruralhometech.com