What is the average cost to install a French drain in New Brunswick?

A French drain installation in New Brunswick costs $1,500 to $4,000 for a typical residential project, with most homeowners paying $2,000-$3,000 for a 30-50 linear foot exterior French drain that redirects water away from foundations, low-lying lawn areas, or garden beds. Pricing depends on the drain length, depth, soil conditions, and whether the drain ties into an existing storm water system or daylight outlet.

The cost per linear foot for a French drain in NB ranges from $30 to $80, with the variation driven primarily by trench depth and soil conditions. A shallow French drain (12-18 inches deep) for surface water collection in a garden or lawn area costs $30-$50 per linear foot. A deeper foundation drain (3-4 feet deep) running along the exterior of a house to address basement water intrusion costs $50-$80 per linear foot due to the significantly greater excavation volume and the need to work carefully around the foundation.

A standard French drain installation includes excavating a trench 12-24 inches wide at the specified depth, lining the trench with filter fabric to prevent soil from clogging the system, laying 4-6 inches of clean 3/4-inch gravel, installing a perforated drainage pipe (4-inch rigid PVC or flexible corrugated pipe) with perforations facing down, backfilling with gravel to within 2-3 inches of grade, wrapping the filter fabric over the top, and finishing with topsoil and sod or seed. The gravel and pipe combination creates a channel that collects subsurface water and directs it to a lower discharge point.

New Brunswick's climate and soil conditions make French drains particularly important — and slightly more complex to install. The 1,100-1,200mm of annual precipitation combined with heavy snowmelt in spring creates enormous seasonal water volume. Clay-heavy soils in the Fredericton river valley and parts of Moncton drain poorly, causing water to pool around foundations and in low lawn areas. The 1.2-1.5 metre frost depth means French drains must either be installed below the frost line (expensive) or designed to drain completely so no standing water remains to freeze and crack pipes. Most residential French drains in NB are installed at 18-30 inch depth and rely on gravity flow to a daylight outlet at a lower elevation.

The discharge point is a critical design element. The drain must have a positive outlet — either daylighting on a slope at least 3 metres from any structure, connecting to a municipal storm drain (where permitted by your local municipality), or draining into a dry well or infiltration pit. NB regulations generally prohibit directing drainage onto neighboring properties or into sanitary sewer systems. A landscaping professional experienced with NB drainage projects will assess your property grade, identify the optimal drain route, and ensure the system has adequate fall (minimum 1% slope) throughout its length. For persistent foundation water issues beyond what a simple French drain addresses, consult a foundation specialist.

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