Basement Lowering in Toronto

Basement lowering and underpinning are the same work described two ways. Lowering is what you get: a deeper floor and more headroom. Underpinning is how it is achieved: extending the existing foundation deeper in engineered sections.

Most Toronto basements start between 6 and 7 feet. Lowering typically targets 7 feet 6 inches or more, which is the difference between storage and a room people will actually use.

Measure your basement properly first

Almost every conversation about lowering starts with a number that turns out to be wrong, because people measure to the wrong thing. Before you talk to anyone, get these three numbers.

Slab to joist. Floor to the underside of the wooden joists, taken in a clear area away from ducts and beams. This is the optimistic number and it is the one most people quote.

Slab to the lowest obstruction. Floor to the underside of the main trunk duct, the steel beam, or whatever hangs lowest in the room. This is the number you actually walk under, and in an older Toronto house it is often six to eight inches less than the first one.

Your target finished height. What you want to stand in, measured from finished floor to finished ceiling.

The depth you need to gain is not simply the difference between the first and third numbers. The new slab assembly takes thickness of its own, typically gravel base, vapour barrier and concrete, and your finished flooring sits on top of that. A crew that digs exactly the depth of your height gap will leave you short.

Why Toronto homeowners lower basements

To create a legal second suite. A basement apartment has minimum ceiling height and room size requirements, and in most older Toronto houses the height is what blocks it. In this rental market a legal suite changes what the property earns, not just how it feels. The legal suite page covers the full requirement list.

To make the space genuinely usable. A 6 foot 4 inch ceiling is a storage room regardless of how it is finished. Above 7 foot 6, it reads as a floor of the house.

As the alternative to moving. Land transfer tax in Toronto is charged twice, municipal and provincial, and on a typical trade-up the transaction costs alone frequently approach the cost of the entire underpinning. The worth-it arithmetic runs both sides of that comparison.

To fix headroom while solving water. The foundation is exposed exactly once in the life of the house. Waterproofing during lowering costs a fraction of a separate excavation later.

How much depth you can actually gain

Most projects lower by 2 to 4 feet. What is achievable on your house is an engineering determination, not a sales answer, and it turns on these:

Existing footing depth and condition. Many older Toronto houses sit on shallow rubble or brick footings. That is exactly why the basements are short, and it is also what the engineer is designing around.

Soil type. Toronto's ground varies street to street. Clay behaves differently from sand, and a house built on fill behaves differently again. Soil is the single biggest source of legitimate variation between two otherwise identical quotes.

The water table. A high water table does not necessarily stop the project, but it changes the drainage design, sometimes the method, and always the cost.

Adjacent structures. A neighbouring foundation, a garage, a porch or a retaining wall close to the wall being underpinned constrains how deep you can go and how the sections are sequenced. This is most acute in semis and row houses.

Services under the slab. Drains, water service and sometimes gas run beneath the floor, and their depth and slope requirements can set a practical floor on how low the new slab can sit.

Be sceptical of any depth promised on a first visit, before anyone has looked at the footings or the soil. The honest answer at that stage is a range and a set of questions.

What height to aim for

The legal minimum and a good basement are different targets, and the cost gap between them is usually smaller than people expect, because the expensive part is mobilising the crew, the engineer and the permit rather than the last few inches of soil.

Lowering by method

Two ways to get there, and they suit different basements:

• Underpinning keeps the full floor area and costs more
• Bench footing costs 20 to 40 percent less and gives up 18 to 24 inches around the perimeter, permanently

For narrow Toronto semis and row houses, that perimeter usually matters, and it can quietly push a bedroom below the room sizes a legal suite requires. For wide basements built as rec rooms, it often does not matter at all. The comparison page walks through the measurement that settles it in about a minute.

A hybrid is legitimate and common: underpin the walls where floor area matters, bench the walls where it does not. Your engineer can design that, and it can take real money out of a project without costing you anything you would notice.

What the project involves

Engineering and permits first, which is 2 to 4 months in Toronto once the 6 to 12 week City review is counted, then 4 to 6 weeks of alternating-section work, then curing. The week-by-week process covers what actually happens on site, and what living through it is like covers the noise, the dust and whether you can stay in the house.

Things to settle before you commit

• The finished height, in writing, measured to finished ceiling
• Whether ductwork is being rerouted, because a flat wide trunk duct can buy you inches more cheaply than digging for them
• Whether waterproofing is in scope, since the excavation is already paid for
• Whether the new slab, vapour barrier and gravel base are included
• Whether a bathroom rough-in is going in, which is far cheaper before the slab than after
• What happens if soil or water differs from assumed, and what the contingency is

Common questions