Drainage & Trenching in Courtenay
Perimeter drains, ditch work and service trenches — dug once, to a depth and a fall that still works in February.
Drainage and trenching work moves water away from a building and puts services in the ground. Courtenay Excavating installs perimeter drains, ditching, and utility trenches across Comox, Cumberland, and Royston, where 1,154 mm of annual precipitation and slow-draining Vashon till put most of the load on the drain rather than the roof. Typical projects run $3,000 to $12,000.
Drainage and trenching in the Comox Valley commonly runs $3,000 to $12,000, with perimeter drains on a standard house at the lower end and long service runs or wet-ground work at the upper. Cost follows trench length, depth, whether the spoil can stay on site, and how much drain rock and filter fabric the ground needs. Machine and operator time is $110 to $160 an hour for a mini excavator and $150 to $250 for a standard machine. Ranges only — a written quote follows a site walk.
Drainage is the least visible thing on a build and the most expensive thing to redo. A perimeter drain installed against a finished foundation costs a fraction of the same drain installed after the landscaping, the driveway and the deck are in.
Why drainage carries so much of the load here
The Comox Valley takes about 1,154 mm of precipitation a year, and the wet season runs October to April. That is less than Campbell River at 1,489 mm and close to Nanaimo at 1,165 mm, but the distribution is what matters — a large share of the annual total arrives across roughly six months, so ground that drains adequately in July can be saturated for weeks in January.
The subsoil decides how much of that water a foundation ever sees. Quadra Sand takes it away without help. Vashon till, the grey compacted clay layer over much of the valley, does not — water perches on the clay and moves sideways until something intercepts it. Floodplain silt near the rivers combines poor drainage with a shallow winter water table.
The practical consequence is that a perimeter drain here is rarely optional insurance. On till and silt lots the drain is the primary reason a basement stays dry.
Perimeter drains, footing drains and what actually fails
A perimeter drain is perforated pipe laid at footing level in clean drain rock, wrapped in filter fabric, falling continuously to an outfall — a storm connection, a ditch, or a sump. Every one of those four elements is a failure point.
The most common failure is silting. Fines migrate into the rock and then into the pipe, the perforations blind over, and the drain stops working long before the pipe itself degrades. Filter fabric and clean, washed rock are what prevent that, and both are places where saving money at install costs a full excavation later.
The second most common failure is fall. A drain that runs level, or worse runs uphill for part of its length, holds water and silts faster. The third is the outfall — a discharge point that floods in winter backs the whole system up. Establishing where the water goes is the first design decision, not the last.
Trenching for services, and doing it safely
Service trenching covers water, sewer or septic lines, power, and communications, and the rules tighten as depth increases. Before any powered excavation, WorkSafeBC OHS Regulation section 20.79 requires the location of all underground utility services in the area to be accurately determined. A BC 1 Call ticket costs nothing, utility members have three working days to respond, and excavation has to begin within 14 calendar days of the request.
Once a worker enters a trench deeper than 1.2 metres, section 20.81 requires the sides to be sloped, benched, shored, or otherwise supported. Quadra Sand makes that non-negotiable — a sand face will stand up looking stable right until it does not. Spoil placement matters too, since a pile close to the edge adds lateral load to the trench wall.
Combining scopes saves real money. A trench opened once for a service line and a drain costs far less than two trenches, and neither has to cross the other's backfill.
How a drain goes in
- 1
Find the water before digging for it — Where surface water arrives from, where the winter water table sits, and where the outfall can go all get established first. A drain with nowhere to discharge is just a trench.
- 2
Locate services — WorkSafeBC OHS Regulation section 20.79 requires the location of all underground utility services to be determined before excavating with powered equipment. A BC 1 Call ticket is free, and utility members have three working days to respond.
- 3
Dig to depth and fall — The trench is cut below the footing and graded to a consistent fall toward the outfall. Any trench over 1.2 metres that a worker enters is sloped, benched, or shored under WorkSafeBC Part 20.
- 4
Bed, wrap and backfill — Perforated pipe is bedded in clean drain rock and wrapped in filter fabric so fines do not migrate in and blind the drain, then backfilled in lifts. Silt is what kills a perimeter drain, not age.
Local conditions
Till and silt lots through Courtenay and along the river flats hold water at the surface and perch it on the clay below, so perimeter drains and cross-drainage do most of the work. Sand lots through Black Creek and Merville drain freely, but trench walls in Quadra Sand slough without warning, which is why WorkSafeBC's 1.2 metre threshold gets hit on ordinary service runs there.
In practice
- Situation
- A 1970s house on the Courtenay River flats with a persistently damp basement wall on the uphill side only.
- Complication
- The original perimeter drain was intact but had silted solid — unwrapped pipe in native backfill rather than washed rock and filter fabric — and the outfall sat below winter ditch level.
- Resolution
- The uphill run was re-excavated and rebuilt with clean drain rock and fabric, and the discharge was rerouted 18 metres to a higher outfall that stays above the ditch in December.
People also ask
How long does a perimeter drain last?
Installation quality matters more than age. A drain bedded in clean washed rock and wrapped in filter fabric can run for decades; unwrapped pipe in native backfill can silt closed in under ten years. On the Comox Valley's till and silt lots, where fines are abundant, the fabric is the difference.
Can a perimeter drain be replaced without digging up the whole yard?
Often, yes. Where the failure is confined to one run — frequently the uphill side — only that section needs excavating. A camera inspection and a check of the outfall usually show whether the problem is localized or system-wide before anything is opened up.
How deep does a service trench have to be?
Depth is set by the utility and by frost and load cover, not by preference. What is fixed is the safety threshold: any trench over 1.2 metres that a worker enters must be sloped, benched, or shored under WorkSafeBC Part 20, and that applies whatever the soil looks like.
Where can a drain discharge to?
A storm connection, a roadside ditch, or a sump and pump where gravity will not do the job. The constraint is winter water level — an outfall sitting below the ditch in December backs the system up exactly when the drain is needed most. Establishing the discharge point is the first step of the design.
Related reading for anyone pricing drainage work: getting the pad drained before backfill, what a drainage quote turns on. Courtenay Excavating also serves river-flat lots inside the city.
Start with the site details
Address, scope, and rough timing are enough for a first range. Drawings help but are not required.