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Weeping Tile, Foundation Drainage and Sump Pumps: How a Dry Basement Is Actually Built
Structure and ICF Water From a builder
Weeping Tile, Foundation Drainage and Sump Pumps: How a Dry Basement Is Actually Built
A basement stays dry because of three things that are all buried on the day the house is backfilled: the drain at the footing, the layer that lets water reach it, and the place the water goes. Get those right and the membrane is a backup. Get them wrong and no membrane saves you.
Short version: The Code requires drainage at the footing of a basement: perforated weeping tile beside the footing, covered with at least 150 mm of clear stone and a filter, draining by gravity to a storm sewer or daylight, or to a sump with a pump. The wall above it needs damp-proofing and, where water pressure is expected, a drainage layer or membrane. The sump needs a sealed lid, a check valve, and in any house that depends on it, a backup pump with its own power. The commonest failures are tile laid above the footing, no filter, a sump pump with no backup, and downspouts dumping beside the wall.
The three parts, and what the Code says about each
| Part | What the Code requires (Part 9) | What good practice adds |
|---|---|---|
| Footing drain | Perforated pipe or tile beside the footing, with at least 150 mm of clean stone over it, and a filter where the soil is fine | 4 inch pipe with the holes down, continuous around the whole footing including under the garage, cleanouts at the corners |
| Wall drainage and damp-proofing | Damp-proofing on the exterior of the wall below grade; a drainage layer or waterproofing where ground water is expected | A dimpled membrane or drainage board on every wall, lapped over the tile; on ICF, the membrane over the foam |
| Outlet | Gravity drain to a storm sewer, a drainage ditch or daylight; or a sump pit with a pump | Gravity to daylight wherever the lot allows (a walkout gives it for free); a sump with a sealed lid, check valve, and backup |
The 2024 Ontario Building Code Part 9 covers drainage and damp-proofing; lot grading and drainage requirements covers the surface water that should never reach the tile in the first place.
Weeping tile done right
- Laid beside the footing, not on top of it; the top of the pipe should be below the top of the footing so the water level in the stone never rises to the slab
- Continuous around the whole foundation; a tile that stops at the garage is a tile that floods the garage corner
- Holes down, so water enters from the bottom and silt stays out
- Clear stone over and around it, at least 150 mm; more is better
- A filter fabric over the stone in silty or clay soils, or a sock on the pipe, so the stone does not fill with fines in five years
- Cleanouts at two or more corners so it can be flushed; a tile that cannot be cleaned is a tile with a lifespan
- Connected to the under-slab stone where there is radon rough-in or a sump, so water under the slab has somewhere to go
The wall above it
Damp-proofing is a coating that stops moisture wicking through; waterproofing is a membrane that holds back water under pressure. On a lot with a high water table or heavy clay, specify waterproofing. On most lots, damp-proofing with a dimpled drainage membrane over it does the job: water that reaches the wall runs down the air gap behind the membrane to the tile instead of sitting against the concrete. On ICF, the membrane goes over the foam and the detailing at the top and at penetrations is what matters. ICF foundation pros and cons explains why ICF basements have a reputation for staying dry; the insulation keeps the wall warm, so there is no condensation on the inside either.
Where the water goes
Gravity is the only outlet that never fails. If the lot slopes enough to run the tile to daylight below the footing level, do it, and put a rodent screen on the end. A storm sewer connection, where the municipality allows one, is the next best. A sump pit is the answer everywhere else, and a sump pit is a machine: it needs a sealed lid (radon and smell), a check valve on the discharge, a discharge that goes well away from the house and does not freeze, a float that cannot hang up, and power.
Power is the problem. Sump pumps fail in the storm that knocks the hydro out, which is also the storm that fills the pit. A battery backup pump or a water-powered backup, tested twice a year, is not optional in a house that depends on the sump. Why new basements leak has the sump pump at the top of the list for a reason.
The mistakes that flood basements
- Downspouts discharging beside the foundation: the roof puts more water against the wall than the sky does
- Grading sloping toward the house after the backfill settles
- Weeping tile above the footing, or crushed during backfill, or with no filter in clay
- Window wells with no drain to the tile
- A sump pump with no backup and no alarm
- A membrane stopped short of the top of the wall, or punctured by the backfill
- Backfill with the clay that came out of the hole, packed against the wall with no drainage layer
Every one of these is cheap to avoid before the backfill and expensive after. Walk the foundation with the builder before the excavator comes back, and photograph the tile, the stone, the membrane and the outlet. The foundation inspection checks most of it; your own photographs check the rest.
Related guides on this site
Sources and further reading
Questions people ask
Is weeping tile required in Ontario?
Yes, for a basement. Part 9 of the Ontario Building Code requires drainage at the footing (perforated tile covered with clear stone and a filter where needed) draining by gravity or to a sump, plus damp-proofing or waterproofing on the wall.
Does a new house need a sump pump?
Only where the footing drain cannot drain by gravity to a storm sewer or daylight. If the house depends on a sump, it needs a sealed lid, a check valve, and a backup pump with its own power source.
What is the difference between damp-proofing and waterproofing?
Damp-proofing is a coating that stops moisture wicking through the wall; waterproofing is a membrane that holds back water under pressure. High water tables and clay soils call for waterproofing plus a drainage layer.
Why does a new basement leak?
Most often: downspouts and grading sending water against the wall, weeping tile laid wrong or clogged, window wells without drains, a membrane that stopped short, or a sump pump that failed in a power outage.
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Reviewed and updated October 2026. Costs are Ontario ranges, not quotes; code references are to the Ontario Building Code in force at that date.
