- 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
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,