Underpinning or benching: which lowers your basement?

The engineer divides the perimeter into numbered sections. The crew digs under one section of footing at a time, forms it, pours a new deeper footing and wall, and lets it cure before the next section is dug. The house is never sitting on an unsupported length of wall, which is the whole point of the sequence. When every section is done, the floor is excavated to the new depth, drainage and a sump go in where the drawings call for them, and a new slab is poured.

The result is a basement with the same footprint as before and a ceiling height that meets code for a suite or a family room.

Benching leaves the existing footings alone. The floor is dug down inside a line set back from the walls, and a sloped concrete bench is poured along the perimeter from the old footing down to the new floor. The bench holds the soil under the old footing in place. The room is lower in the middle and narrower at the edges, and the bench is usually a foot or more wide along every wall.

Three things, in order.

• The neighbour's foundation. On a semi or a house close to the lot line, underpinning near the shared or adjacent foundation needs the engineer's answer on how the neighbour's footing is affected. Where it cannot be done safely, benching along that wall is the fallback.
• The soil and the water. Sand and a high water table make underpinning slower and the drainage more involved. Clay is the simpler case.
• The use of the room. A suite with a bedroom along an outside wall loses that wall to a bench. A gym or a storage room may not mind.

Many GTA basements end up with underpinning on three walls and a bench on the one shared with a neighbour. The engineer draws it, the permit covers both, and the room is as wide as the site allows. Savino Construction does both methods with its own crew, so the choice is made on the site walk and the engineer's drawing, not on which method a contractor happens to sell.