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Dig-out and underpinning prices
HomeGuide puts the cost to convert a crawlspace into a finished basement at $50–$100 per square foot, and underpinning to lower an existing basement floor at $20,000–$50,000. Angi's range for crawlspace conversions is $50–$150 per square foot, about $105,000 on average. HomeGuide says digging out and lowering a basement takes 2 to 5 weeks.
| Basement size | Dig out and finish |
|---|---|
| 800 sq ft | $40,000–$80,000 |
| 1000 sq ft | $50,000–$100,000 |
| 1200 sq ft | $60,000–$120,000 |
| 1500 sq ft | $75,000–$150,000 |
| 2000 sq ft | $100,000–$200,000 |
HomeGuide.
Lowering the floor is the usual fix when the ceiling is below the 7 ft that IRC R305 requires for habitable rooms. Every inch counts: check your current height with the ceiling height checker first.
Getting comparable bids
- Write a one-page scope: rooms, bathroom fixtures, number of egress windows, ceiling type and flooring.
- Ask each contractor to price the permit, the water fix and any electrical panel work as separate lines.
- Ask whether quotes include design, dumpster and final cleaning.
- Compare per-square-foot totals only after removing the bathroom and egress lines, which do not scale with area.
- Check the license, insurance and recent permits of each contractor with your building department.
The usual order of work
| Phase | Who | Notes |
|---|---|---|
| 1. Water and radon | Waterproofer, mitigator | Test radon and fix leaks before anything is covered |
| 2. Permit and plan | Owner, designer | Rooms, egress windows, bathroom location |
| 3. Egress and drains | Excavator, plumber | Cut windows and break slab for drains while the space is open |
| 4. Framing and insulation | Carpenter | Foam on the concrete, treated bottom plates, fire blocking |
| 5. Rough electrical, plumbing, HVAC | Licensed trades | Inspections before walls close |
| 6. Drywall and ceiling | Drywall crew | Leave access panels for valves and cleanouts |
| 7. Flooring, trim, paint, fixtures | Finish trades or owner | Final inspection |
Bathroom and egress costs land early, in phase 3, which is why they surprise people who budget only by the square foot.
Lowering a floor: two methods
Underpinning extends the existing foundation walls downward in short sections, so the whole floor can drop and the walls go deeper. It needs engineering and permits and is the method HomeGuide's $20,000–$50,000 figure describes. Bench footing leaves the walls in place and pours a concrete bench around the inside perimeter, so the middle of the floor can drop. It is simpler but costs floor space along every wall. Either way the new slab needs drainage, often a sump, and new stairs to match the lower floor.
Common questions
How much does it cost to lower a basement floor?
Underpinning costs $20,000–$50,000 on average, according to HomeGuide.
How long does it take to dig out a basement?
HomeGuide says 2 to 5 weeks, longer if there are major obstacles.
Related calculators
Sources
- https://homeguide.com/costs/cost-to-dig-out-a-basement
- https://www.angi.com/articles/crawlspace-basement-conversion-cost.htm
- https://www.cityofboise.org/media/3924/434-irc-code-section-r305-ceiling-height.pdf