The Journal · Basements
Choosing Between Underpinning and Benching
Both techniques lower a basement floor. They are not the same. Here is how the choice between them usually breaks down.
If you have decided that lowering your basement floor is the right move, the next question is how. The two techniques most commonly used are underpinning and benching. They produce different results and they have different trade-offs.
What each technique does
Underpinning extends the existing foundation downward through engineered, sequenced pours under the existing footing. The result is a foundation that is now deeper than it was. The new slab can be poured at the new depth.
Benching keeps the existing footing where it is. A new concrete shelf is poured against the inside of the perimeter wall, sloped down from the existing footing to the new lower slab elevation. The slab is lowered between the benches.
Ceiling height
Underpinning generally gives you more new height than benching. The exact gain depends on the engineer's design and the existing soil and footing conditions.
Benching gives you less height, but the structural intervention is smaller. If your existing basement is already close to a workable ceiling, benching can be enough.
Floor area
Underpinning preserves the full floor area at the new depth. The room you end up with has clean perimeter walls right down to the new slab.
Benching gives you less usable floor area because the bench itself takes up perimeter depth. You typically lose somewhere between a foot and a foot and a half of width along every exterior wall. In some rooms this is fine. In others it is a problem.
Cost and schedule
Underpinning costs more per linear foot of wall than benching and takes longer. The sequencing of the pins controls how fast the structural phase can move.
Benching is faster and less expensive. For projects with limited budget and modest height needs, it can be the right call.
How we recommend deciding
Start with what you want the finished basement to be. If it is a real lower floor of the house, with living spaces, bedrooms, or a kitchen, underpinning is usually worth it. If it is a casual rec room or play space and the existing ceiling is already reasonable, benching may serve you better.
Then have a structural engineer assess the existing foundation. Some foundations underpin well, others present challenges. The engineer's input is part of the decision, not separate from it.