How deep do concrete footings need to be in Moncton NB?

Concrete footings in Moncton must extend a minimum of 4 feet (1.2 metres) below finished grade to get below the frost line and comply with the NB Building Code. This requirement applies to all structural footings — foundations, deck piers, porch footings, retaining wall footings, and any structural post or column footing.

The reason for this requirement is frost heave — the upward movement of soil as it freezes and expands. Water in the soil increases in volume by approximately 9% when it freezes, and saturated soils can generate enormous upward pressure. A footing sitting above the frost depth will heave in winter and settle in spring, causing cracking, structural movement, and damage to everything it supports. Getting below the frost line means the footing bears on soil that stays at a stable, above-freezing temperature year-round regardless of how cold the surface gets.

Moncton's frost depth is approximately 4 feet, consistent with most of southern NB including Fredericton and Saint John. This is the minimum — some engineers and experienced contractors in the area pour to 4.5 feet as a margin of safety, particularly on poorly drained sites or clay-heavy soils that are more susceptible to frost action. Shaded north-facing sites and low-lying areas that hold moisture may also warrant going deeper.

For residential building permits in Moncton, your building inspector will want to see footing depth confirmed — often through an inspection before the forms are poured. The City of Moncton Building and Technical Services department can confirm current requirements for your specific project type and location.

Footings must also rest on undisturbed native soil or properly engineered compacted fill — not loose backfill, topsoil, or organic material. Bearing on soft or organic soil is a separate failure mode independent of frost depth. When excavating to 4 feet in Moncton, contractors regularly encounter fill layers that need to be over-excavated and replaced with compacted granular material before forming the footing. This is especially common in older developed neighbourhoods where previous construction has disturbed the native soils. Always get a professional assessment for structural footing work — foundation problems are expensive to fix after the fact.