Frost heaved my New Brunswick deck posts again, how deep should they go?

Your deck posts need to go a minimum of 4 feet (1.2m) below grade in New Brunswick — and deeper is better, especially inland. Frost heave is one of the most common and frustrating deck problems across the province, and it almost always comes down to footings that don't get below the frost line.

New Brunswick's frost depth varies by region. In Fredericton, Woodstock, and the upper Saint John River valley, you're looking at 4.5 to 5 feet in a hard winter. Coastal areas like Saint John and Shediac are slightly more forgiving — closer to 4 feet — but don't count on it. If you're in Edmundston or Campbellton, plan for the deeper end of that range given the harsher northern winters. The NBC 2020 (now in effect for new applications as of May 1, 2025) requires footings to extend below the local frost depth, and your local building inspector will have the specific design depth for your area.

The footing itself matters as much as the depth. A tube form (Sonotube) filled with concrete and belled at the bottom — wider at the base than the top — resists frost heave far better than a straight cylinder. The bell shape anchors against uplift forces. Minimum footing diameter is typically 10–12 inches for a residential deck, but your engineer or inspector may specify larger depending on the load. Some contractors in NB also use helical piers (screw piles), which are excellent in our freeze-thaw conditions and can be installed year-round.

Concrete timing is critical here. You can't pour concrete when temperatures are below -10°C without heated enclosures, and freeze-thaw cycles in spring and fall can compromise a fresh pour. Your best window in NB is May through September — wait for consistently warm daytime temps above 5°C.

A building permit is required for most deck construction in New Brunswick. If you're in Moncton, contact the City's Planning & Development at (506) 856-4375. In Fredericton, reach Development Services at (506) 460-2020. Saint John homeowners should contact Growth & Community Services at (506) 658-2835. If you're in a rural or unincorporated area, your permit comes from the Regional Service Commission (RSC) for your region — RSC 11 covers the Fredericton rural area at (506) 453-2956, and RSC 7 handles the rural Moncton/Shediac area at (506) 533-3637.

One more thing worth checking: if your existing posts were heaving repeatedly, the soil drainage around the footings may be the real culprit. Clay soils — very common across NB — hold water and amplify frost heave. Proper backfill with granular material (crushed stone) around the tube form helps water drain away from the footing rather than freeze against it.

Browse deck contractors and concrete specialists in our directory at New Brunswick Construction Network — a local pro who knows your soil conditions and municipal requirements can save you from going through this a third time.