Download PDF version (255.9k) Log In or Register to view the full article as a PDF document.
Q.Should the holes in a foundation perimeter drain face up or face down? And does the drain need to be pitched as it runs around the house?

A.Don Marsh responds: There’s no question the holes must face down (oriented approximately at 4 o’clock and 8 o’clock) to drain off any water rising from below. Keep in mind that if the drain is embedded in stone, as it should be, water will run through the stone as well as through the drain. In other words, the stone and pipe work together to drain the water away. You aren’t limited to just the narrow trough of water between the holes in the pipe.

The drain should be placed at least 6 inches below the interior slab. If the holes were facing up, you might be able to carry off more water through the pipe itself, but in order to get into the pipe, the water level would rise dangerously close to the slab.

Ideally, the drain should pitch as it runs around the house, but often this isn’t practical. To get a 1/8-inch-per-foot pitch, one corner of the drain on a 20x30-foot house would have to be 6 inches above the opposite corner, bringing the drain above the slab. To avoid this, the drain can be laid level around the house, but it must not have any dips or rises, and it must pitch away from the house to daylight. A pitch of 1/8 to 1/4 inch per foot is recommended.

Don Marsh is a project manager with Dufresne-Henry Consulting Engineers in Montpelier, Vt.