Do I need an engineer for a retaining wall in NB?

In New Brunswick, retaining walls over 4 feet (1.2 metres) in exposed height typically require engineered drawings as part of the building permit process — walls below 4 feet generally do not, but an engineer is still worth consulting for any wall retaining a significant slope or located near a structure. The NB Building Code reflects the engineering reality that a wall retaining more than 4 feet of soil mass is a structural element, not a landscaping feature.

When a permit is required, your local building department will ask for drawings stamped by a Professional Engineer (P.Eng.) licensed in New Brunswick. The engineer's drawings will specify the footing depth and width, wall thickness, rebar schedule, drainage requirements, and surcharge assumptions (such as whether a vehicle, deck, or structure sits on top of the retained soil). In NB, where frost depth reaches 4-5 feet and soil can become heavily saturated during spring thaw, engineered designs account for the lateral earth pressure and hydrostatic forces that are higher here than in many other Canadian provinces.

Even when an engineer is not legally required, there are situations where hiring one is simply smart. These include: any wall over 3 feet high retaining a slope where a vehicle drives or parks above the wall; walls supporting the soil adjacent to a building foundation; walls near utilities, easements, or property lines; and any wall where failure would damage property, injure someone, or affect drainage to neighbouring lots. The cost of engineering — typically $500-$2,000 for a residential retaining wall drawing — is modest compared to the liability and repair cost of a wall that shifts, cracks, or collapses.

For poured concrete retaining walls specifically, engineering becomes especially important because the design — footing size, wall thickness, rebar placement — must be calculated for the specific soil conditions and height at your site. NB soils vary considerably: clay-heavy soils in the Saint John River valley retain more water and exert higher lateral pressure than sandy or well-drained soils. A wall designed for sandy Moncton soil may be undersized for the clay soils common in the Fredericton area.

Walls in the 3-4 foot range without an engineer are a grey area in NB. Contractors with strong retaining wall experience know the standard design conventions for this height range and can build a structurally sound wall without stamped drawings. Walls under 3 feet that use gravity mass (concrete blocks, interlocking stone) or properly battered poured concrete with good drainage are generally straightforward. The risk increases sharply when the soil being retained is saturated, the slope above is steep, or there is a structure near the top of the wall.

Need help connecting with a retaining wall contractor or finding an engineer for a larger project? New Brunswick Concrete can match you with experienced professionals across NB.