Home Improvement, Remodeling and Repair @ Builders Websource. Home design software, advice, tools, videos, tech notes, links and more!


Home Page | Books | BuildersTALK | Building a Dream | Green Building | Links | Software | Tech Notes | Tools | Contact

Builders Websource Tech Note #051000-1


Click for Payment Instructions
Last Update 06.30.12


Green Building
How-To Books
Links (Web)
Tech Notes


Home Design
Lighting Design

Specialty Tools


Support & Info

About Us
Contact Us

Builders Websource®
Online Price: $5.95 US
PDF Format, 12 Pages, 411 KB

Tech Notes

CPVC vs. Copper
Metal Roofing
Septic Systems
Structural Design
Tankless Heaters
Water Hammer


By reading, downloading or printing this online tech note, you agree to pay the posted licensing fee in accordance with our payment terms and licensing agreement. To keep our prices as low as possible, please note that we DO NOT mail hardcopies. For additional information on our satisfaction guarantee including terms and conditions, please click HERE. Thank you for your patronage. Our authors are very grateful for your support of Builders Websource®.


Rain, melting snow, runoff and condensation are destructive natural forces that can result in significant damage to residential foundations and basements. Since these forces often occur invisibly underground, water infiltration presents one of the most elusive and least understood problems for homeowners. Along the way, this leads to great frustration and expense as homeowners seek ways to prevent water from penetrating everything from roofs to slabs to cellar floors. This Builders Websource technical brief outlines the causes for foundation water infiltration and presents several techniques for preventing and eliminating such conditions in new and existing dwellings.

Special Notes

This technical brief has been adapted, edited and revised with permission from Russell H. Lanoie, Rural Home Technology. Important Notice! Homeowners or contractors with severe drainage conditions should always consult a specialist to engineer remedies optimized for the particular "on-site" conditions.

Table of Contents

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
High Groundwater Table
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.

Go to Table of Contents

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.

Go to Table of Contents


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, Figure A 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.

Figure BConventional perimeter drains are usually constructed as shown in Figure B with 4" pipe laid at the base of the footing. 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 Figure Csitework 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. Figure C shows how the drains were installed. This same procedure is excellent for drying out existing wet basements where conditions permit.

Go to Table of Contents
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.

Broken Pipe
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.


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!

The pipe around the house can be laid level and needs only the slightest pitch to vent successfully, unlike a sewer line which is designed to carry floating solids. 1/16" to 1/8" per foot is more than enough pitch, though steeper is perfectly acceptable. Use perforated or slotted pipe only in the area that needs to be kept dry, especially if the outlet pipe runs near a septic system (see local codes) or there are trees anywhere near its path. WatrLevel is a cost-effective precision leveling tool ideal for installation for French drains and general drainage systemsAn inexpensive tool ideal for ensuring the proper slope is the WatrLevel, now available to homeowners and contractors through Builders Websource. The WatrLevel simplifies the process of setting pipe invert elevations, including around corners -- which is typical in most residential situations.

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 sidehill 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.


The outlet must be located in accordance with regulations regarding distances from septic systems and the neighbor's lot lines. The end of the pipe should have a rodent guard to keep critters from nesting during the dry season in this ready-made hotel. Use 4 pieces of brass wire (which doesn't rust or corrode) spaced about ¾" apart to discourage the critters. Anything finer can plug up with algae and silt that might occasionally wash through the line.

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.

Bedding Material

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.

Slotted Pipe

Since no one makes pipe with 5/16" holes like they used to 25 years ago, you can produce your own slotted pipe by setting a radial arm saw about 3" above the table and slicing through ¼ the depth of solid pipe every two to three inches or so. Wear goggles to prevent flying chips of hot plastic from striking your eyes. Use either rigid polyethylene or good quality PVC pipe that resists shattering when the saw blade passes through. The 1/8" slots that result seem to let in water just fine and yet keep the concrete sand from entering the pipe. Pipe is installed with the slots facing down or turned slightly toward the direction of incoming water.

Go to Table of Contents


Drain pipe

Proper backfilling is important to keep moisture away from the foundation wall. Using clean, porous sandy backfill against the wall will keep water from lingering and finding its way through imperfections. To conserve the amount of sandy material that may need to be brought on site it is possible to add sand directly against the wall and original material (with the large rocks removed) towards the outside of the excavation using alternating buckets of backfill (and compacting these layers) as the excavation hole is filled. The backfill should be topped off with nonporous material (clay or loam) and sloped away from the foundation to prevent surface water from entering the ground next to the wall.

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.

Go to Table of Contents

A note on why I don't use the readily available 4" rolled black pipe: Our local NRCS soil conservation technician recommends against using the stuff in our area because of the amount of iron in our water which stimulates an "iron bacteria" (also often seen in wells) that can plug up the narrower slots. This is why I prefer to slot my own pipe, and also because it is easier to maintain grade during installation using a rigid pipe.

Sump Pumps
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.

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.

Go to Table of Contents

Filter Fabric: Synthetic cloth-like material that is used for several different types of construction related applications such as erosion control, road stabilization and soil separation. Can consist of either woven or non-woven fibers in varying thicknesses or weights. Available in 12 to 15 foot wide rolls several hundred feet in length. Woven fabrics (usually black) resemble the stuff that modern day grain bags and weed control fabric are made from while non-woven fabrics can resemble a range of materials from soft felts to the stiff shiny house wrap (to which they are closely related) usually seen enveloping homes under construction.

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.

Also see the University of Minnesota Extension Bulletin Moisture in Basements: Causes and Solutions

Go to Table of Contents

Filter material: According to the American Iron and Steel Institute's Handbook of steel drainage and Highway Construction Products, 1967:
"Early subdrains consisted of a trench filled with coarse rock ("french" drains) which quickly silted up. Extensive research by the U.S.Waterways Experiment Station at Vicksburg, Mississippi, shows that a graded material roughly equal to concrete sand (AASHO Specs) has been found most suitable. Such material gives better support to the sidewall of the trench and thereby reduces erosion and silting. Filter material should be placed in layers and tamped."

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. 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 three 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.

Plastic Flashing at Foundation Intersection

This technique of installing a membrane just below the ground surface is similar to installing "flashing" around a chimney or other structure on a roof. One of its biggest benefits is that it can eliminate the need to completely excavate a foundation wall all the way to the footing and attempting to waterproof it. It is somewhat similar to installing a full length "splash block" mentioned in other basement drainage articles on the Internet except that it is out of sight.

I've also had success with this technique even when attempts to make the wall watertight below have failed. One case in particular involved a local public building with ninety year old granite block walls. Excavating them completely, steam cleaning, re-mortaring the joints and sealing with some hi-tech black goo did not keep out the water as well as this flashing system that I installed just below the ground surface after the other waterproofing had failed.

Stone in place

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 diging around a house without destroying the landscape, the underground utilities, or his back.

Conventional waterproofing

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.

Also see: Waterproofing, Damproof by Rodney Harkness.


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.

Go to Table of Contents

Sloppy Mortar

On one job I was required to dig up an entire wall only to find that the problem occurred just a few inches below the surface of the ground. The lower part of the foundation was poured concrete (in excellent condition) with exposed granite slabs set on top to support a church. When the morticians (the guys who put in the mortar) had filled the irregular spaces between the granite and the poured concrete, they had let the mortar settle away from the granite just slightly. This tiny gap allowed rainwater  to channel into the basement behind the finished interior wall that hid the whole process from our view on the inside.

To make matters worse, the basement window wells were filling with rainwater from the roof, so much so that it was coming in around the windows. We constructed dry wells below the windows, easily relieving this problem, while the leakage below the granite was stopped by sealing the cracks with masonry and a layer of plastic.

Difficult Challenge

After digging up almost the entire perimeter of a house in a very sandy soil, I came to the conclusion that it was a combination of events that caused water to enter the basement each spring. A deck behind the house was keeping the winter snow from insulating the ground underneath, encouraging frost to penetrate the ground. Since the ground below the deck had frozen, spring rains and melting snow could not to disperse harmlessly away. Since the ground surface was sloping toward the house, water was forced to run toward and alongside the foundation wall. To top it off, there was a seam in the foundation which allowed water to leak into the basement.
Sealing this seam and sloping the grade away from the house eventually solved the problem.

Test Pit

A hole dug to determine soil type, seasonal high water table, and depth to ledge. Some states require a test pit of specific depth (to determine that ledge is a minimum number of feet below bed bottom) while others require only a shallow pit to determine depth to hardpan soils.


In conclusion, the keys to effectively addressing foundation and basement moisture problem are:
  • Proper diagnosis -- assessing whether the source is surface or ground water or warm, moist air condensing on cool surfaces, or a combination of two or more of these sources;
  • Following accepted practices to keep water from entering through the basement wall and/or lower the water table around the structure, and
  • Maintaining the drainage system to make sure that water goes where you want it to!

See: University of Minnesota Extension Bulletin Moisture in Basements: Causes and Solutions

See also: Soil: The Nature of Drainage for a good description of the differences between various types of soil and Soggy Basements.

Go to Table of Contents
Original Copyright © 1997-1998 Russell H. Lanoie

Builders Websource® Technical Note
© 2000 - 2012.  All Rights Reserved.

Go to Table of Contents

ASTM International