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 inch 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.
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.
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.
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.
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. Figure C shows how the drains were installed. 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.
At times it is impossible to place a pipe at or below the bottom of a footing due to immovable obstructions such as boulders or a rock ledge. At times these may actually be cast into the footing. In this case, it is a good idea to pressure wash the rock surface and grout (seal) the rock to the wall with a strong, well bonding masonry product. This masonry seal keeps water from entering under the footing, and is formed into a shape that gradually slopes away to divert water from the rock or ledge to a point where it can be picked up by a conventional perimeter drain system. This technique requires patience and a little luck to be entirely successful, but it is often easier than trenching through solid granite!
Water flowing through a pipe toward the ground surface provides an invitation for tree roots which can enter and eventually block it completely. It is best to use solid pipe with root proof joints to prevent root penetration whenever possible. Schedule 40 pipe (the heavy stuff) should be used wherever there is a possibility of any type of vehicle hitting or crushing it. The outlet should be placed high enough in the outlet ditch or side hill to let water freefall several inches to keep small amounts of buildup from blocking the pipe. It is helpful to make a header of stone around the outlet for protection.
Whenever possible, install a tee or an elbow on the drain line at the origin of the pipe (the opposite end from the outlet) and extend a riser pipe to the surface of the ground next to the house. This riser serves as both an inspection point and an emergency cleanout if ever necessary. Cover the cleanout with a 4" plastic screw-on cap and clearly mark the location. Often it is possible to make the cap flush with the surface of the crushed stone that is used as a splash guard around the foundation, leaving it nearly invisible but easily accessible. It is helpful to make diagrams or take photos to record all such locations. In many cases it is also helpful to place a tall stake next to the outlet (particularly in snow country) in the event it may need to be checked during winter.
Where the drain makes a turn to conform to the foundation (such as a 90" corner), use a gentle sweep as opposed to a sharp 90" connector. The sweep helps to eliminate clogging and simplifies use of a plumbing snake in the event of failure. In addition, periodic cleanouts should be installed after every few 90" turns.
To prohibit 1½" stone from silting up, the stone should be wrapped in filter fabric to hold back the original soil. Water still passes through the fabric but the soil stays in place. Better yet, use a different bedding material that readily passes water but is considerably less expensive. Washed concrete sand, the coarser the better, allows water to flow through readily but keeps the trench more stable than stone while reducing silt buildup in the system. I've used it for 25 years in all but the wettest conditions (where I occasionally use ¾" stone wrapped in fabric) with outstanding results and no call backs. This technique requires using pipe with smaller holes since the half inch or larger holes in standard perforated pipe will not hold sand out.
If the drain pipe cannot be run to a safe outlet area, it may be possible to run the outlet to a dry well on the property that is downhill from the house but high enough above the water table to "relocate" the water on site without it ever being brought to the surface. If this is not possible, it may be necessary to connect the perimeter drains to a collection basin outside of the house. From there, a sump pump can lift and discharge water away from the house. It is helpful to find a place to send the water that is far enough away so that it does not recirculate through the ground into the basement.
Of course, the disadvantage of using a pump is that the dewatering process is entirely dependent on the reliability of the pump and the supply of electricity. I can remember receiving letters from home years ago telling of the recurring disasters to my aunt's house caused by excess water in her basement when her sump pump failed. Freezers full of spoiled food, ruined furniture and the general nuisance of a flooded basement were becoming too much to bear. On one trip home I did some checking and told the folks that a gravity drain could probably solve the problem.
I can remember receiving letters from home years ago telling of the recurring disasters to my aunt's house caused by excess water in her basement when her sump pump failed. Freezers full of spoiled food, ruined furniture and the general nuisance of a flooded basement were becoming too much to bear. On one trip home I did some checking and told the folks that a gravity drain could probably solve the problem.
They went ahead and had one installed and have had no more trouble with unexpected flooding or pump maintenance since. What is surprising is that it took a college education and several years in the construction field before I was able to make such a simple and obvious recommendation. Yet I know of similar situations that exist today, and houses that are being built where sump pumps are expected to do what could have been done with a few pieces of pipe and some planning.
Many basement drainage companies still rely on sump pumps for all installations, regardless of whether or not gravity could be used to discharge the water. This creates a long-term dependence on a mechanical device.
Sump pumps can get plugged up, wear out, fail to come on after months of non-use, or stop because of a power failure. Unfortunately, it is often during the worst weather conditions when power is lost in rural areas while, at the same time, excessive rainfall is causing the water table to rise. About the only assured way to protect a basement is to install a redundant pump and a separate circuit coupled with a battery-powered back-up system that automatically kicks in when all else fails. Such systems are now on the market but represent additional investment and occasional maintenance to keep them in working order. They use an automotive-type battery for power, similar to safety lights in public buildings.
If there is no choice but to install a sump pump, selecting the right pump should be based on the severity of the situation. There are many types market, but the extra money spent for a high quality submersible style with a built-in switch is well worthwhile, especially in extreme situations. Excessive dampness can quickly corrode unprotected motors on pedestal pumps and a power failure that allows water to completely cover an unprotected motor can require replacement of the entire pump. Also, there are automatic switches now available that allow sump pumps to draw water down to within a fraction of an inch of the floor and to turn on when water is only slightly deeper. This can be helpful for occasionally dewatering a basement without digging a sump hole through the concrete floor.
Leaks in Foundation Walls & Maintenance
It is essential to keep the drain outlet running freely. The rodent guard must be kept clear of any debris. The area below the outlet must be kept cleared of leaves and debris, especially if the drain empties into a ditch.
Sometimes drains that have clogged up internally can be cleared by the use of a pressure washer (or even a garden hose) to break up the clog. I've cleared obstructions from perimeter drains and had water drain out of the basement just like water leaving a bathtub.
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.
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 Leakge
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
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. Having been under the direction of an architect in some cases, I've had to follow his recommendations rather than follow my instincts to determine the problems.
Consider this example that involved an old house with a loose stone foundation. The original work that was done under the direction of the architect only aggravated the wet basement problem. Digging a shallow perimeter drain actually allowed more water through the porous basement wall. This was the same mistake many people make when they dig out next to their foundation wall and replace the original backfill with crushed stone either for appearance and splash protection. Putting crushed stone directly over the original soil, even with the installation of a perforated drain pipe often causes more water to enter the ground. The crushed stone becomes a dispersion system in the same way it does in a septic drain field. Usually little water enters the drain pipe, except in a deluge, and more water soaks into the ground next to the foundation where it makes its way into the basement.
What I did to solve the problem was to seal the outside of the wall with a coating of concrete that directed surface water away from the foundation as it soaked into the ground, keeping it from streaming through the loose stone foundation. The addition of a bituminous asphalt coating or a Bituthene membrane can also help to keep water from penetrating the foundation wall.
The success with this project has prompted me to use this technique in many other situations. Rather than using concrete, however, in most cases I rely on a layer of rubber or plastic to direct water away from the wall. Usually I excavate just a few inches below the surface next to the building and 3 to four feet lower at a distance of four to five feet from the wall, sloping the soil down on a 30 to 45 degree angle away from the building as I go. I rake the earth smooth, remove all rocks and sticks, and tamp it firm. Then I install a layer of rubber or a couple of layers of 6 mil polyethylene over the slope, right up to the wall. I don't usually worry about sealing against the wall, as my primary concern is to direct the majority of the surface water away from the wall and out into the earth where it can soak harmlessly away, leaving a "dry zone" beneath the membrane next to the wall.
I use this same technique under a window well if there is any question about the integrity of the wall below the window. I dig out a few extra feet, slope the soil, install the plastic membrane on the slope, place crushed stone as a mini drywell for any rainwater that may enter, install the window well structure and then backfill to the surface as discussed.
In some cases it may be wise to seal the plastic or rubber membrane to the foundation wall -- particularly if there is an excess of water falling from the roof and splashing against the wall. It is also helpful sometimes to place crushed stone over the plastic and install a drain pipe in the stone that runs to a surface outlet to provide water a way to exit without ponding in the stone.
In short, anyone with a water problem in an area which doesn't usually have poor soil conditions should closely examine their situation before insisting on a course of action. It could be the problem may be solved for very little cost, without the need for heavy equipment and the resulting mess. There are few jobs more tedious for a contractor than digging around a house without destroying the landscape, the underground utilities, or his back.
There are times when it is possible to apply a waterproofing / damproofing coating or membrane to the entire wall such as when it is being completely excavated to replace a perimeter drain. If there is any suspicion that the wall is not watertight, this is the time to do something.
While a wall is uncovered I fix obvious cracks, seams, or leaks around utility penetrations because it is far better to do this on the outside rather than the inside of a wall. Such repairs call for cleaning out any loose material and inserting either an expansive hydraulic cement or high quality caulking designed for the purpose. Sometimes it is best to actually widen a crack to get the best performance from the repair material. (There are usually manufacturer's recommendations with these products)
Because the conventional black tar that most contractors use is really just damp-proofing, I often install a layer of 6 mil poly over it when it is still slightly sticky. (This has other advantages to the installer working in a narrow trench on uncertain footing!) I've also used the sticky backed rubber membrane that's been used as a water shield under shingles on roofs for many years. It bonds well to an old, well hardened asphalt coating that has been cleaned well but doesn't like to stick to bare concrete or stay in place over a fresh asphalt coating.
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.