Basement Underpinning & Dig Outs in Washington DC
Licensed in DC and Maryland. Call (202) 695-9533 Get a QuoteBasement Underpinning for DC Rowhouses and Maryland Homes
Finnegan Construction Group LLC is a licensed general contractor handling basement underpinning, dig outs, and basement lowering in Washington DC and Maryland. Most of our underpinning work is in DC rowhouses where the basement is too low to use.
What Is Basement Underpinning?
Underpinning extends your home’s foundation deeper so the basement floor can be lowered safely. The existing footings are excavated and new concrete is poured beneath them in small sections, so the house stays supported the whole time.
Dig Out vs. Underpinning
A dig out lowers the basement slab a few inches without going below the footings. If you only need a small amount of extra height, a dig out may be enough. If you want a full-height basement, you almost always need underpinning, because lowering the floor below the footings requires new foundation support.
Why Lower Your Basement?
More ceiling height. Many DC rowhouse basements are under 7 feet. Lowering the floor turns a cellar into real living space.
More square footage. A finished basement adds living space without an addition.
A rental unit. A legal basement apartment can offset your mortgage.
Resale value. Finished, full-height basements add value in DC.
Our Underpinning Process in DC
- Site visit and estimate. We look at the basement, talk through what you want the space to be, and give you an estimate.
- Test pits and geotechnical report. Once you decide to move forward, we dig test pits at the existing footings. A geotechnical engineer uses them to confirm the size of the footings and the soil bearing pressure.
- Structural engineering. The structural engineer designs the underpinning based on the geotechnical report.
- Permits and neighbor notification. We handle permitting with the DC Department of Buildings and notification for shared party walls.
- Staged excavation and underpinning. Footings are underpinned in sections, with required third-party inspections along the way.
- New slab and waterproofing. We pour the new slab and install drainage and waterproofing so the lower basement stays dry.
- Finishing. Framing, insulation, electrical, plumbing, and finishes to turn the space into a basement you can live in or rent.
Underpinning FAQ
How much does underpinning cost in DC?Most DC rowhouse underpinning projects run $80,000 to $150,000. That includes excavation, underpinning, the new slab, and waterproofing. Engineering and required inspections are additional. A smaller rowhouse sits at the low end, and a larger or deeper job at the high end. We give you a firm number after the site visit and geotechnical report.
How long does underpinning take?Construction usually takes 4 to 5 weeks for a typical DC rowhouse. We underpin in about five stages. For each stage we dig a set of pits, set rebar, pour the new footing, and grout the gap between the old and new footings. Once that cures, we move to the next set. Engineering and permits come first and take longer than the construction itself. We give you a full schedule once the geotechnical report and drawings are done.
Can I stay in my house during underpinning?Often yes, since the work is done in stages and the house stays supported. We will tell you what to expect for your project.
Do I need a permit to lower my basement in DC?Yes. Underpinning requires engineered drawings and a permit from the DC Department of Buildings. We handle it.
Areas We Serve
Washington DC neighborhoods including Bloomingdale, Petworth, Capitol Hill, Brookland, Logan Circle, Adams Morgan, Mount Pleasant, and Columbia Heights, plus Maryland including Takoma Park, Silver Spring, and Chevy Chase.
Get an Underpinning Quote
Call (202) 695-9533 or send your address and project details through our quote form. We also do home additions and basement waterproofing.
