What is the minimum rebar coverage required in NB foundations?

The minimum concrete cover over reinforcing steel in New Brunswick foundations is governed by the NB Building Code (which references CSA A23.1 for concrete structures), and the required cover depends on the exposure conditions — for NB foundations in contact with soil, the minimum cover is typically 75 mm (3 inches) for concrete cast against and permanently in contact with earth, and 40-50 mm (1.5-2 inches) for formed concrete exposed to weather or soil. These requirements exist to protect the steel from corrosion and ensure adequate bond between concrete and reinforcement.

Cover is the distance from the outside face of the concrete to the nearest surface of the rebar — not to the centre of the bar. For a poured concrete foundation wall formed on both sides (the typical residential construction method), the rebar is placed at mid-wall or at specified distances from each face, with the structural engineer's drawings specifying exact placement based on the loading and wall thickness.

The specific cover requirements from CSA A23.1 that apply in NB residential foundation work:

• Concrete cast against and permanently exposed to earth (footings, grade beams, walls placed against soil): 75 mm (3 inches) minimum cover


• Concrete exposed to weather or soil (formed surfaces): 40 mm (1.5 inches) minimum for #15M bar and smaller; 50 mm (2 inches) for #20M and larger


• Concrete in interior locations not exposed to weather: 20-25 mm (3/4 to 1 inch), though this is less relevant for NB foundation work where exterior exposure is the standard condition

Why cover matters in New Brunswick. Concrete cover is the primary defence against chloride-induced reinforcement corrosion. In NB, foundation concrete is exposed to groundwater, de-icing salts from road spray, and coastal salt air in communities like Saint John and Shediac. Insufficient cover allows these chlorides to reach the steel in 10-20 years rather than 50-100 years, initiating corrosion that eventually causes the surrounding concrete to crack and spall from the expansive pressure of the corroding steel.

Footing cover is equally important. NB footings sit on undisturbed soil or compacted granular fill, and the 75 mm cover requirement for concrete in direct soil contact means your bottom mat of rebar should be supported on chairs or approved supports — never placed directly on the soil or excavated surface. A rebar sitting on dirt has zero cover at its contact point and is vulnerable to corrosion from the ground up.

Any structural foundation work in NB should be done by an experienced contractor following stamped engineering drawings that specify cover requirements for your specific project. New Brunswick Concrete can connect you with foundation contractors and help you find professionals serving Fredericton, Moncton, Saint John, Bathurst, Miramichi, and across the province.