How Much Drain Tile Do I Need?

Drain Tile

• Subsurface drainage is needed around building foundations to keep structures dry and carry water away to a safe point. Drainage systems are commonly referred to as drain tile, though plastic pipes are usually used. Concrete or clay sections were primarily used for drain tile until the 1970s, and they may still be the first choice for certain applications. Plastic pipes are made from polyvinyl chloride or polyethylene, and they're available in different versions, to accommodate a variety of drainage methods.

Types of Pipes

• Pipes are available in rigid or flexible, corrugated material, and perforated -- punctured with small holes -- and solid form. Perforations allow water to enter and exit, infiltrating the ground, or discharging to a municipal drain system or open field. Perforated pipes are used for foundation drainage, to collect water from the soil and keep it away from the structure. Solid pipes are used when water needs to be taken away quickly, such as runoff from the downspout.

Drainage Systems

• Underground systems are generally based on gravity flow, where water runs downhill to the exit point. Pipes are installed on a gravel channel, and then buried in gravel. The length of the system depends on the distance between where it begins, and where it discharges -- often a swale, or ditch. Foundation drain tile is placed along the perimeter of the footings, and may discharge into a sump pit in the basement instead.

Drain Tile Quantity Estimate

• Flexible pipe is sold in coils of 100 feet or longer, and rigid pipe in lengths of 20 feet. Concrete or clay drain tiles are usually 2 feet long, and installed with a 1/4- to 1/2- inch space between them. To find the quantity of drain tile needed, measure the distance between where the pipe starts, and the discharge point, and divide by the length of the type of pipe. Add 10 percent to the sum for waste.