Drain Tile

Written for Canada. Plans are metric, but many crews and suppliers work in feet and inches, so this site gives both: millimetres and metres, with feet and inches beside them. Codes are the National Building Code of Canada 2020 (NBC 2020) Part 9 as your province adopts it. A number marked Confirm has not been checked against every province, so check it with your own authority before you act on it.

Reviewed by a working tradesman with 17+ years in the field.

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The perimeter drain collects water at the footing and sends it somewhere safe. Height, stone and outlet decide whether it works.

The big idea

The perimeter drain is the part of the system that actually removes water. It collects water at the footing and sends it somewhere it can safely go. If it is too high, laid badly, or set in dirty stone, water finds its way into the house.

What the code says

From Part 9, Section 9.14, as printed in the Vancouver Building Bylaw 2014:

• The bottom of every exterior foundation wall is drained by drain tile or pipe around the foundation, or by a gravel or crushed rock layer, unless it can be shown to be unnecessary (9.14.2.1).
• Materials: the listed standards include perforated clay and concrete tile, CAN/CSA-B182.1 plastic drain and sewer pipe, and BNQ 3624-115 flexible polyethylene drainage pipe (9.14.3.1).
• The pipe is at least 100 mm (4 in) in diameter (9.14.3.2).
• It sits on undisturbed or well-compacted soil, with its top below the bottom of the floor slab (9.14.3.3).
• Butt joints are laid with 6 to 10 mm (1/4 to 3/8 in) open joints, with the top half of the joint covered by sheathing paper, 0.10 mm polyethylene, or No. 15 felt.
• The top and sides are covered with at least 150 mm (6 in) of crushed stone or other coarse clean granular material, with no more than 10 percent passing a 4 mm sieve.

The text I read gives no slope, no cleanout provisions, and no bedding under the pipe beyond sound soil. Your province's edition may add them. Confirm with your building department and the designer.

Pipe types

• Rigid perforated plastic: holds its fall and resists crushing. A trade guide calls rigid pipe crush-resistant and says its holes are less likely to clog than the narrow slots in coiled pipe.
• Flexible corrugated pipe: allowed if it meets the listed standard (BNQ 3624-115), but it can sag and crush, and rock can crush it during backfill. A trade guide says not to pitch flexible pipe, and to lay it on the footing shelf.
• Whatever you use must meet a standard your code lists. Confirm what your province accepts.

Where it goes and how it falls

• Beside the footing, on undisturbed or well-compacted soil, never on loose fill. Do not put it halfway up the wall or above the footing.
• The top of the pipe is below the underside of the floor slab. A trade guide says perimeter drain pipe should never be above the slab surface.
• Holes down, onto a bed of stone, is the common layout in the trade guides, and the drawing on the Membranes page shows it. One building-science article says a drain with the holes up still works, just less well. The code text I read is silent on this.
• Fall: the code text I read gives none. One trade guide sets rigid tile straight and level, or with a slight pitch toward the outlet. A building-science article says the perforated pipe can be level, and the solid outlet pipe should fall at least 1/4 in per foot (about 2 percent).
• Check the grade with a laser or level while you lay it, not after. No dips, kinks or high spots that hold water.

Example. A solid outlet pipe 20 m (65 ft 7 in) long at 1/4 in per foot drops 20 × 0.0208 = 0.42 m (16 1/2 in). That tells you early whether a daylight outlet is possible on the lot. The run is made up.

Stone and fabric

• Clean crushed stone, with no more than 10 percent passing a 4 mm sieve, at least 150 mm (6 in) on the top and sides of the pipe (9.14.3.3).
• A trade guide gives about 50 to 75 mm (2 to 3 in) of stone under the pipe. The code text I read gives no figure, so follow your drawings.
• Wrap the stone, not the pipe, in filter fabric where fine soil could wash in. The two enemies of a footing drain, according to a building-science article, are fine silt and tree roots.
• Backfill with coarse granular material against the wall, and cap with soil that sheds surface water.

Joints, fittings and cleanouts

• Use proper manufactured fittings for corners and connections.
• Cleanouts: the code text I read has none, but two trade sources say to plan them before you dig, so the drain can be cleaned later. Capped risers at corners are common. Ask your inspector what yours expects.
• Keep downspouts off the foundation drain. A building-science article says tying them in is not uncommon and brings in debris.

Connection to the outlet

• Foundation drains discharge to a sewer, a drainage ditch or a dry well (9.14.5.1).
• Where gravity drainage is not practical, a sump pit and an automatic pump are required (9.14.5.2). The next pages cover sumps and discharge lines.
• A dry well is allowed only where the groundwater is below its bottom, and it must be at least 5 m (16 ft 5 in) from the foundation (9.14.5.3).
• A building-science article says to run to daylight rather than rely on a pump, and to add a second outlet for more than about 60 m (200 ft) of foundation.

Before backfill

• Check the pipe level and fall around the whole building.
• Check the stone depth and cleanliness, and the fabric.
• Check the pipe is not crushed or kinked.
• Check the outlet connection.
• Take photos for your records.

Common mistakes

• Pipe above the footing or the slab
• Pitching flexible pipe, so it dips
• Dirty stone
• No filter fabric where soil could wash in
• Pipe crushed during backfill
• Downspouts tied into the drain
• Blocked or missing outlet