Lower Your Basement, strengthen the foundation under it
Philadelphia rowhomes sit on shallow stone footings, which is why so many basements have six-and-a-half foot ceilings and no legal path to becoming living space. Underpinning fixes that — and because we finish the space too, you hire one contractor instead of two.
Digging Down Without Undermining the House Above
Underpinning means extending your foundation deeper than it was originally built, so the floor of the basement can come down with it. In a Philadelphia rowhome that usually means working under a shallow stone footing, in short sequenced sections, so the wall above never loses support at more than one point at a time.
It is the difference between a basement you store things in and a basement you live in. Most of these houses were built with cellars that were never intended as habitable space — low ceilings, no headroom under the joists, and no drainage worth the name. Lowering the floor by even a foot or two is what makes a family room, an office, a guest suite or a legal bedroom possible.
It is also genuinely structural work. Party walls mean your dig affects the houses on both sides, and the city requires engineered drawings and permits before anyone breaks ground. Our certified foundation specialists handle the excavation, the new footings and the slab; because we are a full contractor, the same crew can frame, plumb and finish the basement afterward.
Six Reasons Philadelphia Homeowners Call Us About Underpinning
Some of these are about gaining space. Some are about the foundation itself. If any of them describe your house, an assessment is the right next step.
What Actually Happens Under Your House
Nobody feels relaxed about excavating beneath their own home. Here is the full sequence, so you know what each stage involves before you commit to anything.
We measure existing headroom, inspect the foundation wall and footing, look at how the joists bear, and check for water history. You get an itemized written estimate at no cost, including whether the job is worth doing at all.
Digging below an existing foundation in Philadelphia requires engineered drawings and city permits. We coordinate the architect and structural engineer and file with the city, rather than handing you a list of people to chase.
The dig happens in short alternating sections, never as one continuous trench. Each section is excavated, formed and poured before the neighbouring one is opened, so the wall above is always supported.
Each section gets a new reinforced footing carried down to the required bearing depth, tied into the existing foundation. This is the part that both gains you height and strengthens what was there.
Before the new slab goes down, we install sub-slab drainage and a waterproofing layer. Skipping this is the single most common regret in a finished Philadelphia basement, and it cannot be added later without breaking concrete.
This is where a foundation-only contractor hands you back a bare concrete box. We keep going — framing, electrical rough-in, plumbing, drywall, flooring and paint — under the same contract and the same schedule.
What You Get for the Money
Underpinning is not a cosmetic project and it is not cheap. These are the four returns that make homeowners decide it is worth doing properly.
Usable square footage you already own
You are not building an addition or buying land. You are converting a floor of the house you already have into space you can actually live in.
A stronger foundation than you started with
New reinforced footings carried to proper bearing depth address settlement at its source, rather than patching the cracks it produces upstairs.
Drainage done at the only right moment
Sub-slab drainage and waterproofing can only be installed while the slab is open. Doing it now avoids breaking up a finished floor in five years.
One contract from dig to final coat
No handoff between a foundation specialist and a finish contractor — which is exactly where budgets, schedules and responsibility usually come apart.
Underpinning Questions Philadelphia Homeowners Ask
Straight answers on cost, permits, timelines and whether your house is even a candidate. Have a question that is not here? Call us and ask it.
How much does basement underpinning cost in Philadelphia?
Underpinning in the Philadelphia area typically runs from about $10,000 to $25,000 or more, depending on how deep you need to go, the linear footage of foundation involved, and the condition of the existing footing. Adding the finishing work — framing, electrical, plumbing, drywall and flooring — to create a usable room generally increases the total. The variables that move the number most are depth, access for removing spoil, whether party walls require additional support, and whether drainage and waterproofing are included. Engineering and permit fees are separate line items and should always be itemized rather than buried in a lump sum. We provide a free written estimate broken out by stage, so you can see the structural cost and the finishing cost separately and decide how far to take the project.
Do I need a permit to lower my basement in Philadelphia?
Yes. Excavating below an existing foundation is structural work, and Philadelphia requires permits along with drawings prepared by a licensed architect and structural engineer before any digging begins. This is not a formality that experienced contractors skip — unpermitted structural work can block a future sale, void insurance coverage, and in rowhome construction it puts the neighbouring properties at genuine risk. The engineer specifies the depth, the reinforcement, and the sequence in which sections may be excavated. We coordinate the architect, the engineer and the city filing as part of the project rather than leaving you to assemble that team yourself. If a contractor offers to lower your basement without permits or an engineer's stamp, that is the clearest possible signal to keep looking.
How long does underpinning take?
The excavation and concrete work itself is usually a matter of weeks rather than months, but the honest answer is that the permit and engineering stage often takes as long as the digging. Because underpinning has to proceed in short alternating sections — excavate, form, pour, cure, then move to the next section — the schedule is driven by curing time as much as by labour. Finishing the space afterward adds its own timeline for framing, rough-ins, inspections and final finishes. We give you a stage-by-stage schedule with the estimate so you can see where the fixed waiting periods fall. Depth, foundation condition, access for removing excavated material, and city review times are the four things most likely to shift the dates.
Is my rowhome foundation strong enough to dig out?
Most early-twentieth-century Philadelphia rowhomes can be underpinned, but it depends on the specific footing and it is not a question anyone should answer over the phone. These houses typically sit on shallow stone foundations with parging, and the assessment looks at the footing's depth and condition, the soil beneath it, how the floor joists bear on the wall, and the state of the party walls shared with your neighbours. Some foundations need additional support work before excavation can start; occasionally the honest recommendation is that the project is not worth the cost. A structural engineer makes the final determination based on our site assessment. We would rather tell you it is a bad candidate at the estimate stage than discover it halfway through a dig.
Can you add a bathroom to an unfinished basement?
Yes, and doing it during underpinning is the right time. A below-grade bathroom needs enough depth below the slab to run the waste line to the sewer connection at the correct fall, which is often the constraint in an un-lowered basement. When the floor is already coming out, that depth becomes available and the drainage can be set properly instead of relying on an ejector pump as a workaround. Because we hold the plumbing license in-house, the rough-in is done by our own licensed master plumbers as part of the same project rather than subcontracted around the concrete schedule. Basement bathrooms are one of the most common things we are asked for alongside a dig, and one of the biggest value adds to a rowhome.
Who handles the underpinning and who handles the finishing?
We do both, which is unusual. Most Philadelphia homeowners who lower a basement hire twice — a foundation or waterproofing specialist for the structural work, then a general contractor to frame, plumb and finish the room. That means two contracts, two schedules, and a seam between them where responsibility becomes ambiguous if something goes wrong. Bottom Side Plumbing and Other Things is a multi-trade contractor with certified foundation specialists and licensed master plumbers on the same team, so the underpinning, the drainage, the rough-ins and the final finishes all sit under one contract with one point of accountability. If there is a problem in the structure or in the finish work, it is the same phone number either way.
Find Out If Your Basement Is a Candidate
We will measure your headroom, look at the foundation, and tell you honestly whether underpinning makes sense for your house — with an itemized written estimate at no cost.