As a contracting group specializing in basement underpinning in Toronto, we often get asked this simple question, “what is underpinning?” Below is a brief answer to that question.
“Underpinning” is an industry term that’s generally used to describe reinforcing an existing foundation. This may be to shore-up a structure that was poorly built originally or has degraded over time, is subject to subsidence or land-slippage, or is being prepared to carry extra weight. Underpinning is also performed when a homeowner wants to have their basement foundation dug out to increase the ceiling height of their basement. This is also known as basement lowering.
.What’s That Got to Do with Basements?
Contractors usually become involved with underpinning basement walls because a home owner decides to deepen them to create a full height basement. In this instance, they are sometimes originally little more than crawlspace below a floor. At other times, the plan may be to deepen a basement built for storage, so as to create living space with livable head-height.
Simply excavating out the floor could upset the balance of the foundations, as they slide inwards and crack the walls above. That’s why it’s necessary to dig under them to create a new foundation. Basement underpinning solves the problem of “which comes first, the chicken or the egg?”
Stages in the Process
If there was a single basement job not recommended for amateurs or the uninsured), then basement underpinning has to be the one. Get it right, and you’ll add significant value to your home. Get it wrong though, and you could end up damaging the fabric of your house.
Appoint a licensed structural engineer with a record of completed jobs, to prepare statutory documents and obtain approval for the job.
Appoint a basement-underpinning contractor who’s similarly experienced to complete the following work:
- Remove a small section of the existing foundation to obtain access underground, and replace it with a load-bearing joist.
- Excavate alternate strips to the required depth, and pour shuttered reinforced concrete beneath the exposed sections of foundation.
- When the new foundations are completely cured, complete the balance of the basement underpinning.
- Lay a new floor when everything is stable, and build out the interior of the extended space.
Houses are valued in terms of living space. A new basement could therefore increase the value of your home by up to 10% – and you get more living space too. Basements are especially popular when it comes to extending homes, because they retain existing footprints, and seldom affect the neighbors.
However, you are effectively building your house “upside down” by adding the walls and floor when the roof’s up already. While the job’s in process the structural integrity of the entire building is compromised in the short-run. If it fails, then your new basement could end up costing you a whole lot more than it’s worth.
Of course, you should take out extra insurance while the work’s in progress. But no insurer will compensate you for loss caused by an incompetent builder you chose yourself. It’s highly recommended to find an experienced basement under-pinner who is licensed (and insured themselves).