What Kind of Pipe Do I Use for an Underground Downspout?

Corrugated Pipe

• Four-inch corrugated pipe is commonly used because it's very inexpensive and easy to work with. Due to its flexibility, it doesn't require elbows during installation. Lay the pipe in a ditch and backfill with gravel. The pipe should have a continuous slope in the direction you want the water to travel. Corrugated pipe comes in perforated and non-perforated types. The perforated style has slots cut into it to allow water to drain out. It's used when you want to percolate the water back into the soil. The non-perforated type is used to transport water to a desired discharge location.

ABS Pipe

• ABS pipe can be used for underground downspouts. This is the hard, black plastic pipe typically used in waste plumbing systems inside the home. It's relatively expensive and requires elbows if the pipe needs to change direction. It's installed similar to corrugated pipe but must be glued at its joints.

PVC Pipe

• PVC pipe can be used for underground applications. It's the white plumbing pipe used for waste plumbing and furnace venting and typically used when the downspouts discharge into the main drain for the house plumbing. This arrangement is not recommended because it has a risk of flooding your basement. If the pipe becomes clogged with debris, water is forced up through the basement floor drain.

French Drain

• The ideal location to discharge downspout water is into an underground French drain. These are essentially large holes filled with gravel. The water is piped to the drain, where it percolates back into the soil. It should be built 20 feet to 30 feet from the building's foundation. The size of the French drain depends on the soil type and amount of water during the heaviest rainfall. It's always wise to build a French drain larger than you think.