French Drains & Sub-Surface Drainage

A French drain is a simple idea done carefully: a trench, filter fabric, drainage rock, and a perforated pipe that carries water to an outlet where it can safely leave. Done right it disappears into the lawn and works for decades. Done wrong it silts up in two years.

When you need one

• A low area with nowhere to drain — surrounded by higher ground or fence lines
• Water shared between neighbours along a property line
• A back yard that stays wet for days even after regrading
• Downspouts and sump discharge that need to be carried away from the house

How we build it

1. Find a real outlet — a lower point on your lot, a rock pit, or a City-approved connection. No outlet, no drain.
2. Trench to a consistent fall (about 1%) with the Bobcat.
3. Line the trench with non-woven filter fabric — this is what stops it silting up.
4. Bed and surround perforated pipe in clean drainage rock (not sand).
5. Wrap the fabric over the top, backfill, and restore the sod or gravel above it.

We also install catch basins for spot collection and run rigid pipe for downspout and sump-pump discharge so the water actually leaves your yard.

What's in the trench

Materials that make it last

Component	Why it matters
4″ perforated pipe	Sized for typical residential flow; slotted to collect water along its length
Clear drainage rock (¾″–1″)	Washed, angular rock so water moves freely around the pipe — no fines to clog it
Non-woven filter fabric	Keeps soil out of the rock jacket without blocking water — the single biggest factor in whether a drain silts up
Solid pipe at the outlet	The last run to daylight or a catch basin is solid, not perforated, so it doesn't re-release water before the outlet

How much does a French drain cost in Calgary?

A residential French drain typically runs $2,500–$7,000 depending on length, depth, how far the outlet is, and what's above the trench (lawn is easy, a patio is not). We quote it as its own line so you can see exactly what it costs.

Common questions

Will a French drain fix a wet basement?

It helps by keeping surface water away from the foundation, but a wet basement is a foundation/weeping-tile issue. We do the yard side; a foundation specialist does the wall side.

How deep does it go?

Usually 45–60 cm, deeper if it has to reach a lower outlet. It has to stay below the frost-heave zone for the sod above it and maintain fall the whole way.

Does it need maintenance?

If it's built with filter fabric and clean rock, essentially no. The fabric is the difference between a 20-year drain and a 2-year one.

Can it freeze and back up in winter?

A drain that's deep enough and has real fall to a working outlet keeps moving water past the point where it would sit and freeze. Most winter backups we see trace back to a shallow trench or an outlet that was never really below the drain — both are things we check before we dig.