Do poured concrete retaining walls in New Brunswick require drainage behind them, and what does improper drainage do over time?

Yes, poured concrete retaining walls in New Brunswick absolutely require proper drainage behind them. Without drainage, hydrostatic pressure from groundwater and seasonal freeze-thaw cycles will cause the wall to crack, bow, or eventually fail completely.

New Brunswick's Maritime climate makes drainage even more critical than in drier regions. Our heavy spring snowmelt, frequent rainfall, and saturated soils during spring thaw create enormous water pressure behind retaining walls. When this trapped water freezes in winter, it expands and applies additional lateral force that can crack even well-built concrete walls.

Proper drainage for NB retaining walls includes several components. A perforated drain pipe (weeping tile) should run along the base of the wall, surrounded by clean gravel and connected to a suitable outlet — either to daylight, a storm drain, or a dry well. The backfill should be free-draining material like crushed stone or coarse gravel for at least 12-18 inches behind the wall, with filter fabric separating this drainage zone from the native soil to prevent clogging. The wall itself needs weep holes every 6-8 feet to allow water to escape, typically 3-4 inches above grade.

What happens without proper drainage is predictable and expensive. Initially, you'll notice minor cracks as hydrostatic pressure pushes against the wall. These cracks allow more water infiltration, which accelerates the freeze-thaw damage. Over 3-7 years, the wall begins to bow outward as the soil pressure overcomes the wall's structural capacity. Eventually, the wall can fail catastrophically — tilting, cracking extensively, or even toppling. I've seen retaining walls in Moncton and Fredericton that looked solid for five years, then failed suddenly during a wet spring when the water table was high.

The repair costs far exceed the initial drainage investment. Rebuilding a failed retaining wall costs $40-75 per linear foot per foot of height, plus excavation and disposal of the failed wall. Meanwhile, proper drainage adds only $8-15 per linear foot to the original construction. For a typical 30-foot residential retaining wall that's 4 feet high, proper drainage costs an extra $300-500 but prevents a $6,000-12,000 rebuild.

Hire a professional for any retaining wall over 2 feet high. Drainage design depends on soil conditions, water table level, and site grading — factors that require experience to assess properly. Walls over 4 feet require engineering in most NB municipalities, and the engineer will specify comprehensive drainage requirements. The consequences of retaining wall failure include property damage, safety hazards, and potential liability issues that make professional design and construction essential for anything beyond basic landscape walls.