Excavating A Cellar
What if an entire floor of your home was dark, damp, and scary. So much so you didn’t want to set foot in it. What a waste of space that you could be using as an office, or a studio, or a gym. That’s what many people are doing with their dark, scary, and damp cellar spaces. One big obstacle is often the height of the ceilings and the solution is usually to excavate and dig down to create more height and add an entire extra floor of livable space in your home.
Before we can go on we have to address the elephant in the room, what do you call it? A cellar? A basement? Both? In NYC, officially, a basement is a story of a building that is below curb level but with at least one-half of its height above curb level. A cellar is a space that has more than one-half of its height below curb level. So typically in NYC what many people refer to as the basement is actually the cellar. The basement is the story of the house, like a garden level, that has windows and doors and already meets code as a living space. So we are talking about the cellar.
A work in progress excavation and benching project
The first thing that you’ll need for this type of project is an architect and a structural engineer. There are many code considerations and structural concerns that need to be addressed, so although we’ll talk about basics, you’ll rely on the professionals to figure out the details.
Excavating your cellar involves removing the slab and a few feet of soil. It’s a difficult and dirty job. The first thing your structural engineer will consider is how deep your house’s foundation walls go. They will likely want to dig a probe hole next to the foundation wall to determine its depth. It’s very common for the foundation walls to not be deep enough below the floor of your existing cellar to extend as low as you might want to excavate. That’s a problem that needs solving. You can’t excavate lower than your foundations walls go.
Cement Benching in place, before cement slab is poured
There are typically two techniques your structural engineer will take to solve this issue: Underpinning or benching.
Underpinning involves carefully excavating the soil under the foundation walls in sections, building forms, and pouring concrete to extend them down to the desired depth. It can sometimes be difficult when your house shares a foundation wall with a neighboring house. Your neighbor may not be willing to give you permission to undermine their home's foundation to create your cellar home gym.
An alternative would be benching. Rather than removing the soil under the foundation walls, you leave it undisturbed to continue doing the job it’s had for likely over a century, but encase it in a concrete bench. The bench extends all the way around all of the foundation and acts like a retaining wall for the load bearing soil under the foundation footings. The soil in the other side of the bench can be removed to the desired level to create the extra height. One drawback is that the bench is often about 2 feet wide which eats up some of the usable square footage of your cellar.
You can raise the ceilings in your cellar to the same height as the other floors on your home. It’s possible to create a clean, pleasant, and dry space. It can be an entire extra floor of living space. It can also be an expensive endeavor, clocking in at $60,000-$100,000 depending on the extent of the scope. But for most people who take it on, having an entire floor of their home too freighting to enter is a price too high to pay, and the expense is worth it.