Can I pour a monolithic slab foundation in New Brunswick?

A monolithic slab foundation — where the footing and floor slab are poured as one continuous piece — is technically possible in New Brunswick, but it faces a serious practical obstacle: the NB frost depth requirement of 4 to 5 feet makes true monolithic slabs extremely uncommon for residential construction here.

The idea behind a monolithic slab is that the footing and floor slab are integrated, eliminating the cold joint between a separate footing and the slab poured on top of it. This approach works well in mild climates where frost depth is minimal — places like Georgia or Texas where you only need to go 12 to 18 inches deep. In New Brunswick, the required footing depth of 4 to 5 feet means the "monolithic" concept quickly turns into a very thick, expensive edge thickening that defeats most of the cost savings.

The NB Building Code requires all structural footings to bear below the frost line. For a slab-on-grade that uses a thickened perimeter as its footing, that perimeter would need to extend at least 4 feet below finished grade in Moncton, Fredericton, and Saint John — more in Bathurst or Edmundston. The thickened edge becomes a deep grade beam, and at that point you are essentially building a frost-protected shallow foundation (FPSF), which is a recognized building system but requires specific insulation design to keep the soil beneath warm enough that frost does not penetrate to footing depth.

Frost-Protected Shallow Foundations (FPSF) are the legitimate NB alternative that achieves something similar to a monolithic slab approach. By insulating the perimeter and underslab area with high-density extruded polystyrene (XPS), an FPSF can place footings at 18 to 24 inches depth rather than 4 to 5 feet — but only if designed by an engineer to CSA A23.3 and the National Building Code climate data for your specific NB location. This system requires precise thermal calculations and is not a DIY project.

For most NB residential construction, a poured concrete full foundation with a separate basement slab, or a crawlspace foundation, is the standard approach that local contractors and building inspectors are most familiar with. If you're exploring slab-on-grade construction in NB — common for garages, workshops, or additions — get a local structural engineer involved early. The savings in excavation can be significant if done correctly, but the design must account for NB's frost conditions from day one.

New Brunswick Concrete can connect you with concrete professionals who have experience with slab foundations and can discuss the right approach for your specific site.