Using Drywells To Collect and Divert Water

"Here are a  few letters that refer to residential drywells.  Hopefully this information will be helpful to those in need!!"     NH

Dear NH,

I suspect I have a leak outside the house in an underground sprinkler system. I'm okay on finding and fixing that.

However, during strong rains and coupled with the suspected sprinkler leak, I get a small (3') puddle of water in the basement. The location of the leak is at the bottom of the foundation wall where the concrete floor meets the poured wall (not cinder block but poured concrete). It appears as though the expansion board material, which was placed between the poured wall and the floor "wicks" water from below the foundation wall/basement floor. I live in a semi-arid part of the US; rain comes in the form of heavy summer thunderstorms. I have a 36" or so sump hole, but no pump. The water level in the sump hole is about 8-10" deep and has consistently remained so since purchasing the house in mid-1995 (The home was one year old when purchased).

I seek information on how to seal, patch, fix the area of the foundation/basement floor where the water enters. Water enters at consistently the same location (about a 24-30" wide area) which is also directly below an uncovered deep well-type basement window casing. More precisely, when moisture first appears, it does so within a predictable 8'-12" area of the expansion board along the floor/foundation joint.



You may have answered your own question. The uncovered window well would seem to be the source of your problem. With many basement leaks, the cause is on the surface of the ground. Rain water has cut itself a easy path from the window well to the base of your foundation. Because of the area of the country you live in, you may not have any waterproofing on the exterior of your foundation, so that plus the expansion board allow an easy entry point for the water.

You can purchase a fabricated plastic cover, available in many sizes, for your window well. This is the easiest and cheapest option.

Another option is to install a drain within the well to collect the water. This would require a place for the water to go, however, and if your land is very flat, you might have to investigate installing a dry well. A dry well is simply a contraption you build under the ground to act as a temporary holding area for excessive water. Some people have used buried steel drums, or even a tapered pile of stacked cement blocks surrounded by gravel, to form the well. A pipe is run into the center of the hollow "well" from the drain installed at the offending location. When it rains, the water is diverted into the well, located a good distance from the foundation, where it will sink harmlessly into the ground.

I have never seen an expansion board as you describe, so I can only assume that this is something peculiar to construction in your area of the country. I can't speak to whether there is a way to seal this material from leaking, so you will have to get a local opinion on that matter.

There are other options. Here is the text of an answer to another person's question... another El Nino victim, that might be helpful…

Dear NH,

For the first time since I bought this foreclosure home a year ago, I have a flooded basement (1/2" of water over 1000 sq. ft. space). The house is 6 years old with a full basement and is located in area close to the water level, however, unlike most houses in the area it does not have a sump system . The walls are dry. A crack in the foundation slab seems to be the source of the water. Also contributing is a French drain system at the base of the exterior stair well that has never worked (despite cleaning it out), allowing water to pool and enter under the basement door. Even after the unusually heavy rains (complements of El Nino) stopped, the water continues to seep up. I know I need to direct the water from the roof away from the house by improving the gutter drain system, but what else can I do? What about busting up the concrete and making a sump system located at the base of the exterior stairs. I did see water trickling in from between the cinder blocks at the stair well's base, and it is located on the same side of the house as the crack in the slab. Might this work? If so, how do I construct one? Can I fill the crack in the foundation well enough to stop water entry?

Any help would be appreciated.




Only by trial and error can you tell whether a small repair can solve your problem. You could try to repair the crack with hydraulic cement, which is a fast drying waterproof Portland cement compound designed to be applied to active leaks. I have use this with varied success on a number of occasions. This is a simple and straightforward product to use. Just follow the directions on the package.

However, water will find a way, and if the water table is up to the level of the slab, nothing but a sump pump will lower the water level enough to keep this problem under control. The operative word is "control". Many homes have sump systems that work seasonally... very busy for a few months and quiet the rest of the year.

Installing a sump is a simple as cutting a hole through the slab (you can rent the tools at any rent-it center), digging a hole at least 18" deep, and putting a pump in the hole. You could also go to a plumbing supply store or home center and inquire about a sump kit that would include the pump as well as a sleeve and cover for the sump hole.

Putting such a system at the base of the stairs is not a good idea. It would be underfoot and possibly a safety hazard. You might be able to cut the basement floor and install a pipe from the drain to the sump, killing two birds with one stone.

I have seen some homes where the sump itself is enough to correct the problem. However, if the water is entering from all around the foundation, a more extensive repair may be required to protect your home.

1) In some homes, the sump is connected to drain pipes installed around the outside base of the foundation. The contractor should also install a water barrier on the outside of the foundation to insulate and seal it. This is the most expensive solution, but the best because it stops the water before it gets under your basement floor, reducing the amount of water vapor entering the basement.

2) Another option is a drain system that involves the installation of channels around the inside perimeter of the basement walls. Holes are drilled through the walls specified intervals behind these channels, which are glued to the floor with waterproof epoxy. Water that leaks through these holes is directed to the sump, where it is pumped away. This system is effective, but does introduce more water vapor into the basement than the exterior drain system. It can also fail if the epoxy releases, and, because it is exposed, must be protected from damage.

Next to a simple sump, this is the least expensive of the available retrofitted waterproofing systems. I have never seen this product available direct to the consumer, but only as part of a franchised waterproofing business. You will have to "let your fingers do the walking" in the phone book to see if this service is offered by any contractors in your area.

3) Drain pipes can be installed on the inside of the foundation under the slab, allowing you to avoid the expense and headaches of exterior excavation, removal of any trees or plantings, etc. A slot is cut into the slab around the perimeter of the basement. A trench is dug down to the footers, and weep holes are drilled through the walls below the slab. Perforated drain pipes are buried in the trench and routed to the sump. They are covered with stone to allow drainage, and the slab is repaired. Water from the weep holes moves through the stone to the drain pipes, makes its way to the sump, and then pumped out of your life.

This is more labor intensive than the "channel" approach but has the advantage of being more permanent and "out of sight". It also allows less water vapor to enter the basement, decreasing the amount of dehumidification needed."

Hope this has been helpful.


Dear NH,

I am installing drainage tile to improve drainage in a wet area. The soil is heavy clay. If I drain the water through the tile to a hole full of rocks, How deep does the hole have to be? Or, do I need to direct the water to a ditch?



As deep as your heart desires, as long as you don't reach the water table or China. There is no standard depth for dry wells that I have ever heard of, except that it should be at least as deep as the frost line.

One way to do this is to dig your hole to accommodate a large steel drum without a bottom and with perforations in the sides. Fill the drum with large gravel, and surround the outside of the drum also with gravel.

Another way is to build a cone of solid cement blocks. The basic layout is a circle of blocks maybe 4 feet or more in diameter on the bottom of the hole. A second layer is place on top of the first, but with one or two less block, to form a smaller circle. Do this up to within a foot of the surface. You will have to experiment with the block to get the best layout based on the depth of your hole.

Run the drain pipe into the highest course, and cap the blocks with roofing paper and a piece of slate or flagstone. Surround the outside of the dry well with gravel, and then cover the whole thing with soil. This should last for many years.

You should, of course, check with your local building inspector or sanitarian to be sure this type of drainage is approved in your area, or if there is an alternate method that is more acceptable.