What’s The Difference Between Underpinning and Bench Footing?

If you live in a metro area like we do here in Toronto, land is at a premium.  When an expanding family is looking to increase the living space in their home, they usually either choose going up (adding another floor), or going below (increasing the height of their existing basement).

When it comes to underpinning a basement, also called basement lowering, the advantage is that you already (somewhat) have existing walls to create your new addition.  It’s often less expensive than adding an addition to your home, and since your building within the existing structure, there is far less red tape to deal with.

The problem with older homes is that the basement was never meant to be a living space.  It was intended for storage, utilities, laundry, and a nice dark and damp home for spiders to creep about.  The height of the basement is often lower than the rest of the floors, coupled with the fact that duct work and utility pipes are usually run along the ceiling area.

Creating a full height basement is not an easy job.  To lower your basement, you’ll need to underpin the foundation so that your house doesn’t fall over like this one did in Toronto.  You’ll need a permit, a structural engineer, and an experienced structural contractor who has experience with underpinning a basement.

When you decide to create a full height basement for your home, there are two methods that can be used.  Underpinning and Bench Footing, both of them are acceptable ways to create a full height basement, and both of them have their pros and cons.  Creating a full height basement is a complex and expensive job, so you should understand the differences when you go over your options with your contractor.

Build a Stepped Bench-Footing

Bench Footing costs less than underpinning as it doesn’t require you to dig underneath the existing footings.  In this method, the existing footings and soil remain untouched.  What happens is that a new foundation is poured on the inside the existing one, all the way down to the depth of the new basement floor.  This creates a second wall inside your basement, leading to a decrease in basement square footage and a ledge equivalent to the added height of the basement.

That’s why they call it Bench Footing, you now have a bench running along the perimeter of your basement.  Some people will make creative use of the space, creating cupboards on top of the bench, while others will simply build a wall above the Bench Footing.

The width of the Bench Footing depends on the increase in height you want for your basement.  For every foot of height you add to your basement, you will need to add about a foot of width to your Bench Footing.  So if you add 18″ of height to your basement, you will have a Bench Footing 18″ in width.  These considerations need to be taken into account, especially if you will need several feet of space added to your new basement.

Foundation Underpinning

Underpinning is more expensive than Bench Footing, but allows you to retain all of your basement square footage since there is no need to build a bench wall inside your basement.  It’s a difficult job, and one not left to fly by night contractors.

Underpinning involves excavating and pouring new footings to the depth where your new basement floor will be.  This is done in sections, and the load of the foundation is carefully transferred and supported as each section is completed.  It’s a slow and careful process as you’re basically undermining the integrity of the foundation during the basement lowering process.

There are several other advantages to this model. First and foremost the basement footprint remains the same but you get the extra headroom. Moreover if you had the slightest doubt about the state of the original foundations that concern’s gone forever. This is the preferred engineering solution, though budget and other considerations may not call for it.

To Summarize the Situation

Bench-Footing is Quicker	Underpinning is Stronger
Bench-Footing is Less Expensive	Underpinning Costs More Money
Bench-Footing Bypasses Foundations	Underpinning Strengthens Foundations
Bench-Footing is the Thief of Space	Underpinning Maximises Space

 

The differences between underpinning and bench-footing are pretty obvious. The Underpinning may be the ideal solution whereas the Bench Footing may be the only affordable one. Look before you leap into this pond of water. If you have questions about creating a full height basement for your home (if your in Toronto and the surrounding GTA), fell free to contact us for a free inspection and estimate.