Restoration Register

Heritage foundation repair in Toronto and the GTA

A rubble stone foundation is meant to breathe. The standard basement waterproofing package, with cement parging inside, membrane outside and a sealed slab, traps moisture in the wall and pushes it up into the masonry above, where it does far more damage than the damp basement ever did.

Pre-1900 buildings across the GTA sit on rubble stone or early brick foundations laid in lime mortar, and the failures are consistent: mortar washed out of the joints, a sagging sill plate above, a wall bulging inward under lateral load, and a previous owner's cement parging holding water in. Correct repair is repointing in lime mortar, rebuilding sections that have lost their bond, replacing rotted sill plates with the building jacked and supported, and using breathable parge and finishes. Underpinning to gain basement height is a common GTA project and it is a structural job, needing an engineer's design and a contractor who has done it under a standing heritage building rather than a basement outfit working from a template.

What to ask before you hire

  1. What will you parge and point with? If the answer is standard cement, the wall will hold water and the brickwork above will pay for it.
  2. Is an engineer involved, and who is it? Underpinning, and any wall that is bulging or moving, needs a design rather than a contractor's judgment call.
  3. How will you support the building during the work? Ask to see the shoring plan and how long the structure will sit on it.
Grant funding

Foundation work is eligible under most GTA programs where it is conservation rather than new basement space. Repointing and structural stabilisation usually qualify and digging out a new basement usually does not, so confirm with heritage staff first.

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