Basement Dig-Outs and Foundation Underpinning in Denver

Lowering Your Basement Floor

Most Denver-area homes built before the 1990s have basement ceilings in the 6'6" to 7'2" range, which doesn't meet current livable-space code and feels cramped for finished use. A dig-out lowers the existing slab, typically by 1 to 3 feet, by excavating soil from inside the foundation and underpinning the footings so the house stays structurally supported while the floor drops. This is different from a walkout conversion or an addition dug from the exterior; the whole operation happens inside the existing foundation footprint, which means careful sequencing, dust control, and a plan for hauling spoil out through a window well, Bilco door, or cut opening.

We see this most often in Denver, Wash Park, Park Hill, and the older ranch and bi-level stock in Lakewood and Arvada, where owners want a full basement apartment or livable square footage and the existing clearance just won't support it. Soil in these neighborhoods is frequently expansive clay, which has direct bearing on how we engineer the underpinning and what drainage measures are non-negotiable.

Underpinning vs. Bench (Pony-Wall) Footing

There are two basic approaches to lowering a basement floor, and the right one depends on your existing footing depth, soil conditions, and how much height you need to gain.

• Traditional underpinning: We excavate in short sections beneath the existing footing, pour new concrete footings at the lower depth, and transfer the home's load onto the new footing before moving to the next section. This gets you full usable floor space at the new depth with no loss of floor area, but it's labor-intensive and costs more.
• Bench footing (pony wall): We pour a new footing and short stem wall inside the existing foundation line, set back from the original wall, and lower the floor only within that new perimeter. It's faster and less expensive, but you lose 12 to 18 inches of floor space around the entire perimeter, which matters in smaller basements.

Bench footings make sense when the budget is tight or the existing footing is already fairly deep and you only need a modest height gain. Full underpinning is the right call when you're maximizing square footage for a future basement finishing buildout, adding a bedroom and bathroom, or planning to use every inch of the space.

The Structural Engineering

This is not a project you start without a Colorado-licensed structural engineer involved from day one. Denver's expansive clay soils mean every underpinning plan needs a geotechnical soils report, or at minimum a review of existing soil data for the lot, before footing depths and sizes get finalized. The engineer designs the new footing dimensions, rebar schedule, and underpinning sequence, and that stamped plan is what Denver, Lakewood, Aurora, or whichever jurisdiction you're in will require for permit.

Underpinning also frequently intersects with other structural modifications, especially if you're removing a center support beam, adding a point load for a new layout, or cutting an opening for an egress window. We coordinate all of that under one engineering package rather than permitting it piecemeal, because changes to the footing system affect how loads transfer everywhere else in the foundation.

Waterproofing and Drainage

Lowering a basement floor changes its relationship to the water table and surrounding soil pressure, so waterproofing isn't an afterthought here, it's part of the structural plan. We install a new interior perimeter drain tile system at the new footing level, tied into a sump pit and pump (often dual-pump with battery backup, given how much Denver basements depend on that system during spring snowmelt and summer storms). Footings and new stem walls get damp-proofed or fully waterproofed depending on grade conditions, and we re-evaluate exterior grading and downspout discharge as part of the scope, since a lowered floor has less margin for error if surface water isn't directed away from the foundation.

We also test and often upgrade radon mitigation during this phase, since you're already opening up the slab and it's the easiest time to run or reroute a radon system, which matters given how common elevated radon readings are across the Front Range.

Sequencing, Safety, and Realistic Cost

Underpinning is done in a strict sequence of small sections, usually 3 to 4 feet wide, alternating along the foundation so the house is never left without support under any continuous stretch of wall. Each section is excavated, formed, poured, and cured before the adjacent section is touched. Shoring and temporary bracing are used throughout, and we monitor for movement as we go. This is slow by design; rushing it is how foundations crack or settle.

For a typical Denver metro home, a full basement underpinning project runs roughly $200 to $400 per linear foot of foundation for the structural work alone, with total project costs (excavation, hauling, waterproofing, engineering, permits) commonly landing between $100,000 and $250,000 depending on square footage and depth gained. Bench footing systems run 30-40% less. Timelines generally run 8 to 16 weeks for the structural and waterproofing phase, before any interior finish work begins. If you're considering this kind of project, request a free assessment and we'll walk the foundation with you and give you numbers specific to your soil, footing depth, and goals.

Related: basement finishing, structural modifications.