Foundation Drain Tile Installation
Foundation Drain Tile Installation
Foundation drainage tile systems are one of the most important aspects of residential construction. Drain tile systems are also one of the most misunderstood aspects. Because these systems are usually deeply buried and cannot be easily modified or corrected, it is vitally important that they are installed correctly. Foundation drainage systems which are installed properly can serve a dual roll.
Many homes around the nation have full or partial basements. These basements are really reverse swimming pools. In other words, most people don't want water in their basements. Foundation drain tile systems act as the means by which ground water can be transported away from your basement. If you want a dry basement, you must have an adequate foundation drainage system.
The water content in the soil surrounding your house can fluctuate seasonally. There is always a point at which you can dig and hit water. Geologists often refer to this as the water table. This water table rises and falls in response to the amount of precipitation in any given time period. The water table in many parts of the country can rise to within a few feet of the surface during wet spells. Water will take the path of least resistance. It can choose to go sideways through a crack in your foundation, or it can go down alongside your foundation into a pipe. I'm sure that you will agree that it is a better idea for the water to go down the pipe.
A foundation drain tile system has four main components. The drain tile (pipe), the filter media (gravel), the gravel cover, and the water outlet. All of these elements must be installed for the system to function properly.
The drain tile or pipe is usually 4" in diameter and is perforated or has pre-drilled holes along its length. Depending upon the type, it can be purchased in rolls up to 250' or in 10'sections. Fittings are available to allow you to go around corners or interconnect the pipe.
The filter media or gravel is used to cover the drain tile. Water can flow readily through this gravel and find its way to the pipe. Remember, water takes the path of least resistance. Some soils (heavy clays) resist water movement. If your soil is like this, the water would rather go sideways into your basement than down through the clay soil to the drain tile. The gravel that is used most often is large (1 - 1 1/2" diameter) washed rounded gravel.
The gravel cover is a barrier which keeps silt and mud from clogging the gravel or the draintile pipe. During excavation, dirt removed from the hole is "fluffed." This means that it is disturbed and broken up. It is loosened further during back filling procedures. All of these small dirt particles (silt) can be easily carried through the gravel by the rain water or snowmelt which enters this soil. Without a barrier, these silt particles immediately clog the gravel and drain tile and render it useless. A wide majority of builders often do not install this barrier. The materials commonly used are straw or tar paper.
The water outlet is simply the place where the collected water flows to. It can be one of three places. If you build on a hillside, your drain tile will simply 'daylight' or come to the surface. This is the best situation, because your system depends entirely on gravity to work. If you build on level ground, you have basically two choices, install a sump pit or a large buried French drain. A sump pit is usually installed inside the basement of your home. The drain tile pipe runs beneath the footer to this sump. The collected water is then mechanically pumped from the sump. A French drain is a large subterranean pit filled with gravel. The drain tile pipe runs to this pit and the water fills this pit. French drains do not work well in areas where the water table rises above the level of the basement floor.
Drain tiles work most effectively when placed along side of a foundation footer, instead of on top of the footer. This practice allows you to lower the effective water table an additional 6-8" below your basement floor. In new construction, install the drain tile immediately after the footer forms are removed. Cover the pipe with gravel to a level flush with the top of the footer. If you choose to wait until the foundation is poured, there will be less room to work in, the side walls of the excavation could cave in, or extra concrete from the foundation pour could fall into the hole and have to be removed. Believe me, it is faster and easier to install it without the foundation walls in the way.
After the foundation walls have been water proofed you begin step two. Backfill over the pipe with at least a three foot thick layer of gravel. If you can afford it, backfill with gravel to within 18" of the finish grade. You must think long term. Remember, it will be virtually impossible to dig up and add gravel in the future when your basement is leaking. The extra money is well worth it.
Once the gravel is in place, cover it with a 4" thick layer of straw or a single layer of 15# roofing felt paper. This barrier will prevent the silt from the backfill dirt from clogging the gravel and drain tile.