What slope should weeping tile have, then?

The Code does not give one. If your contractor builds in a fall, that is their method and it is a sound one; it is not a compliance requirement and its absence is not a defect.

My drain is flat. Does it need replacing?

Not on that basis alone. What would justify it is what a camera finds — standing water in a dip, silt, root mass, a broken section. Flatness by itself is not a finding.

Is this the same as the slope on my sewer line?

No, and that is the source of most of the confusion. A sanitary drain carries a flow and has slope rules. A foundation drain collects water along its length and is specified by depth, bedding and cover instead.

Does the discharge need to be lower than the pipe?

Water still has to leave somewhere, and the Code names a sewer, a ditch or a dry well. Where gravity will not do it, the Code's answer is a pump rather than a steeper pipe.

What fall should weeping tile have? Someone told me mine is flat and that it is why it failed.

Does a perimeter drain need a slope?

Direct answer · reviewed 2026-10-13

Not a specified one. The Building Code sets out how foundation drainage pipe is installed in some detail — what it may be made of, that it is at least 100 mm, that it sits on undisturbed or well-compacted soil below the floor slab, that it is bedded and covered in at least 150 mm of clean crushed stone, how wide the joints may be and where the water is allowed to go — and a minimum fall is not one of the requirements. That surprises people because a sanitary drain does have slope rules, and the two get assumed to be the same kind of pipe. They are not. A sanitary drain carries a flow from one end to the other; a perimeter drain collects water out of the soil along its whole length. What it needs is to be low enough and not to sag, which are different properties from slope.

Conditions and exceptions

A flat drain is not automatically a failed drain, and a sloped one is not automatically a good one. What a camera finds is standing water in a dip, and a dip is a bedding problem.
This is the Code's requirement, not a design opinion. A contractor may build in fall on purpose, and that is a perfectly reasonable thing to do.
If someone has told you your drain failed because it is flat, ask what they saw. That claim is usually made before anything has been looked at.

Drain problem assessment Scope, clean, repair or replace

Local evidence

Every figure below is quoted from the source shown or is our labelled estimate. Verified dates are the day we last checked the source; a figure whose check is overdue is withheld rather than shown.

How deep the drain has to sit: On undisturbed or well-compacted soil, with the top of the pipe below the bottom of the floor slab or the crawl space ground cover; A drain laid higher than the slab cannot drain the water that reaches the floor; Province of British Columbia (BC Codes) · quoted · verified 2026-09-22
Does the drain pipe have to sit at the bottom of the footing?: Not necessarily — the Appeal Board found it is not necessary for the drain pipe to be at the bottom of the wall or at the level of the footing, provided it is below the level of the floor slab; The Board decided this on the facts before it, on a stepped section of foundation wall · It does not license a pipe laid above the slab, which is the genuinely defective case; Building Code Appeal Board, Province of British Columbia · quoted · verified 2026-09-22
Crushed stone over the pipe: At least 150 mm of crushed stone or other coarse clean granular material, with no more than 10% passing a 4 mm sieve; “Clean” matters: fines wash in and blind the stone, and the drain silts up; Province of British Columbia (BC Codes) · quoted · verified 2026-09-22
Where a foundation drain is allowed to discharge: To a sewer, a drainage ditch or a dry well; A dry well may be used only where the natural groundwater level is below the bottom of the dry well, and must be at least 5 m from the foundation (Sentences 9.14.5.3.(1) and (2)); Province of British Columbia (BC Codes) · quoted · verified 2026-09-22

What the Code does specify, in full

It is worth seeing the list, because the absence only means something once you can see how much else is there. The pipe must be at least 100 mm. It must be one of seven named materials. On how it is laid: On undisturbed or well-compacted soil, with the top of the pipe below the bottom of the floor slab or the crawl space ground cover

On what goes around it: At least 150 mm of crushed stone or other coarse clean granular material, with no more than 10% passing a 4 mm sieve Butt-jointed tile has its own rule about how wide the gaps may be and what covers the top half of each one.

And on where the water goes: To a sewer, a drainage ditch or a dry well

Size, material, depth, bedding, cover, joints, discharge. That is a detailed specification for a buried pipe, and nowhere in it is a number for fall.

Why a collector is not a carrier

The instinct that a drain must run downhill comes from the other pipes in a house, and it is right about them. A sanitary drain is moving a known flow from a fixture to a sewer, and if it is too flat the solids stop moving. Slope is doing real work there.

A perimeter drain is doing something else. Water is in the soil all along the foundation, and the pipe's job is to give it somewhere easier to be than the soil. It enters through holes or open joints over the pipe's whole length. There is no upstream end where the water starts.

What makes that work is being lower than the thing you are protecting — which is exactly what the Code asks for, in the form of a depth rather than a gradient.

Level is the property that matters, and the Board has said so

There is a ruling directly on this, and it is about elevation rather than fall. Not necessarily — the Appeal Board found it is not necessary for the drain pipe to be at the bottom of the wall or at the level of the footing, provided it is below the level of the floor slab

Read what that permits and what it does not. The pipe may sit higher than the footing; it may not sit above the slab. The test the Board applied was a level, not a gradient.

The practical version: a drain laid dead flat but genuinely below the floor, on soil that does not settle, in clean stone, discharging somewhere lower, is a working drain. A drain with beautiful fall over most of its run and one sag where the trench was backfilled badly is not, because the sag holds water and silt and that is where it blocks.

So what actually goes wrong

Three things, and none of them is the absence of a designed slope. Bedding that settles, which turns a straight pipe into a dip. Fines washing into the stone until it no longer passes water — the Code's word clean is carrying weight in that sentence. And roots, which find open joints because open joints are what the pipe is for.

All three are visible on a camera and none of them is visible from a drawing. Which is the honest reason to scope before anyone quotes: not to measure the fall, but to find out whether there is a dip, a blockage or a collapse, and where.

Questions homeowners ask

What slope should weeping tile have, then?: The Code does not give one. If your contractor builds in a fall, that is their method and it is a sound one; it is not a compliance requirement and its absence is not a defect.
My drain is flat. Does it need replacing?: Not on that basis alone. What would justify it is what a camera finds — standing water in a dip, silt, root mass, a broken section. Flatness by itself is not a finding.
Is this the same as the slope on my sewer line?: No, and that is the source of most of the confusion. A sanitary drain carries a flow and has slope rules. A foundation drain collects water along its length and is specified by depth, bedding and cover instead.
Does the discharge need to be lower than the pipe?: Water still has to leave somewhere, and the Code names a sewer, a ditch or a dry well. Where gravity will not do it, the Code's answer is a pump rather than a steeper pipe.

Your next step

Flat or not, what decides the job is whether there is a dip, a blockage or a collapse.

Find out what is actually in the pipe

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Sources

British Columbia Building Code 2018, Division B, Section 9.14 — Drainage — Province of British Columbia (BC Codes), accessed 2026-09-22
BCAB #1345 — Location of foundation perimeter drain pipe (18 April 1994) — Building Code Appeal Board, Province of British Columbia, accessed 2026-09-22

Code and municipal requirements are quoted from the sources above; price ranges are what named local companies publish, and the companies that publish them sell the work. Nothing here is a diagnosis of a particular house: only a camera in your own drain can tell you what is wrong with it. Report a correction.