How we build it

1. Trench along the wet, low edge of the driveway. We typically dig about 300 mm (12 in) wide and 450–600 mm (18–24 in) deep.
2. Line it with non-woven filter fabric, which lets water through but keeps silt out.
3. Lay a 100 mm (4 in) perforated pipe on a thin bed of washed drain rock, with a steady fall of at least 1% (about ⅛ in per ft), the minimum slope NDS gives in its installation instructions.
4. Fill around and over the pipe with washed drain rock and wrap the fabric over the top.
5. Put a cleanout at the top end (and at any bend) so the line can be flushed.
6. Turn to solid pipe at the low end and run it to a level spreader: a dead-level rock trench on the contour that lets water overflow as a thin sheet across vegetated ground. The outlet has to sit lower than the pipe. NDS's instructions make the same point: the emitter has to sit lower than the inlet, or water can't get out. See it drawn, step by step →

What it doesn't do: it won't stop surface water running down a steep driveway's wheel tracks. That's the job of rubber water bars. Muddy surface water also slowly clogs a French drain, so we keep surface runoff out of it where we can.

Does it fit your property?

A soakaway pit instead of a spreader? Only if a percolation test shows the soil drains. The New Hampshire Homeowner's Guide to Stormwater Management describes a simple test, and says soil that drains at least ½ in (13 mm) per hour, and within 24 hours, suits soaking water in. In clay, it usually doesn't.

Rules that apply to a French drain (Mission, BC)

• Drain rock counts as soil. Mission's Soil Management Bylaw counts gravel and rock as soil and exempts up to 100 m³ (131 yd³) a calendar year (s.12(a)). The drain rock adds to the gravel for the driveway rebuild, so we count both.
• No concentrating water onto a neighbour. The same bylaw (s.15) says work must not send water onto adjoining land at a greater rate than before, or interfere with a neighbour's drainage. BC courts also take a dim view of collecting water and discharging it onto a neighbour's land (a law firm overview, not legal advice). That's why our outlets spread water out on your side.
• No fill within 3 m (10 ft) of a property line unless a qualified professional signs off, under s.15 of the Soil Management Bylaw. Trench spoil and the outlet's rock stay back from the line.
• New digging counts toward the 200 m² cap. In Mission's forest ecosystems development permit area, a permit is needed once new disturbance passes 200 m² (2,153 ft²) in a calendar year inside the urban growth boundary. The trench and outlet count; a typical driveway French drain is well under that.
• Stay out of streamside areas. Anything within the 30 m (98 ft) riparian assessment area beside a stream needs a professional assessment and a City permit first. And never connect the pipe to a creek or ditch: under the same regulation, a ditch connected to a stream by surface flow counts as part of the stream.
• Not into the roadside ditch. Mission's Sewer Bylaw treats ditches as watercourses, and any work in the road allowance needs City Engineering approval.
• Rock pits may need an engineer. Mission's Required Residential Inspections sheet says rock pits built under a building permit must be engineered. Ask the City whether that applies before choosing a soakaway.
• Building or plumbing permit? A drain that doesn't connect to your house drains or a City pipe usually isn't a building or plumbing matter. We confirm with the City for each job.
• No muddy water into streams. The Fisheries Act prohibits putting a harmful substance anywhere it may enter water frequented by fish. We put silt fence below open trenches and close them the same day where we can.
• Call before you dig. BC 1 Call for buried utilities, plus your own well, septic and water lines.

More on streamside rules: Riparian areas and drainage rules in Mission.

Upkeep

• Flush the cleanout every year or two.
• Keep the level spreader clear of leaves and brush, and keep plants growing below it.
• Walk it in a heavy rain: water should leave the spreader as a thin sheet, not a stream.

How it works with the other options

• It always sits beside the rebuilt driveway surface.
• On a steep driveway, pair it with rubber water bars so surface water doesn't run down the tracks.
• If the problem turns out to be mostly surface runoff, a rock swale with check dams is usually the better fit, and a short French drain can still be added later where the ground stays wet.

Last reviewed October 2026. General information only. Site conditions vary, so confirm details on site and with your municipality.