Can a Basement Floor Be Lowered?

This blog discusses Basement Lowering. Topics Include Underpinning, Bench Footings, The constructions process, and more.

When you’re looking for ways to create additional living space in your Toronto-area home you may want to consider basement lowering (Also known as underpinning).

Underpinning is the process of lowering a basement floor to create a functional space. This is an ideal option if your current home has low ceilings or crawl space.

A key advantage to underpinning is the limited red tape involved. There are fewer government requirements for underpinning than there are for home expansion; making it a shorter, less stressful, and more cost-effective option.

What is the construction process of lowering a basement?

  • The first step of basement lowering is breaking up the existing concrete floor.

  • Once the floor has been removed the soil can be excavated to a lower depth.

  • During this process the foundation footings will be exposed, however, digging will continue until the pre-determined floor depth is hit.

  • After cleaning and levelling off the soil at the new depth the concrete floors, footings, and foundation walls will be poured.

  • At that point, the basement can be waterproofed and renovated (This will be touched upon below).

When the extended foundation walls are found in the pre-existing basement an additional wall will be poured inside the foundation’s perimeter. This wall will overlap the pre-existing footings and create a bench ledge. A bench ledge combined with a knee wall strengthens the structure and acts as a retaining wall for the outside soil.

What happens after you lowering your basement?

After supporting the outside soil, the basement should be properly waterproofed with interior drain tiles to help keep moisture at bay (This waterproofing method is a recommendation, other methods can be used).

Crushed stone, a reinforcing grid, and a vapour barrier will then be placed and levelled before a new floor is poured.

Lowering your basement floor is an excellent way to make a functional and livable space, however, IT IS NOT something you should tackle without the aid of a qualified concrete/ foundation contractor. The task requires special tools, engineering, construction methods, and plenty of experience to be done safely.

When lowering a basement, you may want to redesign the new space. To do this in a cost-efficient manner you should add your drains, walkouts, insulation, stud wall partitions, and other improvements at the same time. This will avoid the need for a renovation in the future.

What Permits and Papers do I need to get my basement lowered?

Building permits along with drawings from a structural engineer.

Are their different methods when lowering a basement?

The two common methods of basement lowering are benching and underpinning. Benching is usually the least expensive of the two, however, underpinning is more common when the homeowner wants to lower the basement by a height greater than 1 foot.

It is important to be aware that the underpinning process may disturb the stable soil supporting a neighbour’s footings. In this case underpinning may not be the best option. If this is the case, the neighbouring foundations should be underpinned at the same time.

Nusite Tip:

Make sure the new basement floor isn’t under or close to the water table. A home's floor should be a minimum of 2 feet above the water table.

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