Perimeter Foundation Drains

Every foundation below grade should be equipped with an exterior perimeter drain. Always work out a drainage plan before digging to locate cleanout and daylight locations of perimeter footing drains (Figure A).

Figure A: Perimeter Drainage Plan
Plan drainage, including cleanout and daylight locations, before digging. On wet sites, plan on knockouts through the footing to connect to a drain under the slab.
Plan drainage, including cleanout and daylight locations, before digging. On wet sites, plan on knockouts through the footing to connect to a drain under the slab.

Perimeter foundation drainage must always be planned in conjunction with well-draining backfill (see Soil Drainage and Bracing before Backfill, Placing Backfill).


Placing Footing Drains

Place drain “tile” — typically 4-in. Schedule-C PVC or ABS pipe — with the holes down on a bed of gravel.

The gravel surrounding the drain should be wrapped with a geotextile, or filter fabric, to keep fine particles from clogging the drain tile.

Place drain tile straight and level, or with a slight pitch toward the exit. Do not attempt to create a pitch when using flexible drain tile, because undulations in the level can cause clogging. Flexible drain pipe should be placed on the footing shelf to prevent dips and sags (Figure C). In either case, perimeter drain pipe should never be above the surface of the slab.

Tile should drain to daylight. If this is not possible, install a sump basket and a sump pump that discharges above ground away from the building (Figure B).

Figure B: Interior Sump Basket
An interior sump basket picks up excess water flowing through sleeves in the footing. A submersible pump discharges the water at ground level away from the foundation.
An interior sump basket picks up excess water flowing through sleeves in the footing. A submersible pump discharges the water at ground level away from the foundation.

Figure C: Placing Footing Drains
The best location for rigid drain pipe is alongside the footing (at left, top and bottom). Ideally, the drain should be at least 6 in. below the top of the slab and always covered by at least 6 in. of stone. If tile is placed below the footing, do not place it too close to the footing or water may undermine the footing (at right, top). To keep flexible drain pipe from developing low spots, place it on top of the footings, making sure that the top of the pipe is not higher than the top of the interior slab and that it is covered by a 12-in.-deep bed of stone (at right, bottom).
The best location for rigid drain pipe is alongside the footing (at left, top and bottom). Ideally, the drain should be at least 6 in. below the top of the slab and always covered by at least 6 in. of stone. If tile is placed below the footing, do not place it too close to the footing or water may undermine the footing (at right, top). To keep flexible drain pipe from developing low spots, place it on top of the footings, making sure that the top of the pipe is not higher than the top of the interior slab and that it is covered by a 12-in.-deep bed of stone (at right, bottom).


Drainage Forms

Perimeter drainage can be provided with stay-in-place footing forms, such as Form-A-Drain® — to ensure a level perimeter drain. These systems usually provide a larger capacity than typical foundation pipe systems.


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