What are the different methods of basement underpinning and which is most common in New Brunswick homes?

The three main methods of basement underpinning are traditional mass concrete underpinning (also called pit underpinning), screw pile or helical pier underpinning, and bench footing underpinning, with traditional mass concrete being by far the most common method used in New Brunswick homes. Each method has different applications, costs, and suitability depending on your foundation type, soil conditions, and how much depth you need to gain.

Traditional mass concrete underpinning is the standard approach across NB and the method most local contractors are experienced with. The process involves excavating beneath your existing foundation footings in small alternating sections, typically 3 to 4 feet wide, one section at a time. Each excavated section is dug to the new desired depth, a footing is poured at the bottom, and then new concrete walls are poured or formed up to meet the existing foundation. Once that section has cured sufficiently (usually 48 to 72 hours minimum), the next section is excavated. This leapfrog pattern ensures the house above is always supported by undisturbed foundation on either side of the active work area. After all wall sections are extended, the full interior is excavated to the new depth and a new basement slab is poured. This method costs $30,000 to $80,000+ for a full basement in NB and is the most proven approach for our soil conditions.

Screw pile (helical pier) underpinning uses steel piles that are mechanically screwed into the ground beside the existing foundation to transfer the building's load to deeper, more stable soil. This method is more commonly used for foundation stabilization and settlement repair rather than for gaining headroom. It can be combined with a lowered slab to create more basement height, but it does not extend the foundation walls themselves. Screw piles are useful in areas with poor bearing capacity near the surface, which can occur in some Moncton-area sandy soils and in Fredericton's river valley soils. However, for the primary goal of gaining headroom, screw piles alone do not achieve the same result as traditional underpinning.

Bench footing underpinning (also called angle underpinning) is a partial approach where a new, deeper footing is poured at an angle from the base of the existing footing down to the new floor level, creating a sloped concrete bench along the perimeter walls. This method is less disruptive and less expensive than full underpinning, but it reduces the usable floor area because the bench takes up space along the walls. It is sometimes used when only a modest depth increase is needed (6 to 12 inches) and budget is a major constraint.

In New Brunswick, traditional mass concrete underpinning dominates for several practical reasons. NB's older housing stock from the 1960s through 1980s commonly features concrete block foundations with relatively shallow footings, and the most effective way to deepen these is the proven pit method. NB contractors have decades of experience with this technique across the province's varying soil types, from Saint John's heavy clay to Moncton's sandy loam to the rocky soils of northern NB. The method also naturally integrates with the waterproofing work that is essential in our Maritime climate, since the new deeper footings can include updated weeping tile and drainage systems.

Regardless of method, all underpinning in NB requires stamped structural engineering drawings and a building permit. This is major structural work that affects the entire load path of your home. If you are considering underpinning, New Brunswick Basements can match you with contractors experienced in the specific method best suited to your home and soil conditions.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Thirty Four Renovations
• Gionetterenovations