First: is the shell ready to finish?
Before any interior work we check four things, because each one is cheaper to fix now than after drywall:
- Engineering and permit status. In Franklin and St. Charles counties a shell built without a permit has to be permitted before the interior can be inspected; in Jefferson likewise. In Warren the structure permit should exist; in Lincoln there is no county permit but the fire district will want to see the electrical. If the shell was built from a kit not engineered for Seismic Design Category C and the county's wind/snow values, the county may require an engineer's letter.
- Slab. Footings to the 30-inch frost line, a vapor retarder under the slab, and a slab that is flat enough for interior walls and finished floors. A shop slab poured without a vapor retarder will sweat under flooring.
- Condensation. A bare steel shell in January drips. The insulation and air-sealing plan has to be set before framing: closed-cell foam on the steel, or a vented assembly with a proper vapor retarder, never fiberglass stuffed against cold metal. See insulation and condensation.
- Utilities. Septic permit and system, well, and electric service have to exist or be scheduled; a finished interior with no approved septic cannot get a certificate of occupancy in the code counties and cannot get the lender's final draw anywhere.
What finish-out includes
Interior framing to your plan; rough and finish plumbing; electrical with a panel sized for house and shop; HVAC (heat pump, furnace, or mini-splits — the shop usually gets its own); insulation and vapor control; drywall, texture, paint; interior doors and trim; flooring; kitchen and bath cabinetry, counters and fixtures per an allowance schedule; appliances per allowance; inspections and CO where applicable; walkthrough.
Not included unless quoted: structural corrections to the shell, slab replacement, septic/well/driveway (quoted separately if you need them), exterior changes.
Price bands (2026, St. Louis ring)
| Scope | Per sq ft of living area |
|---|---|
| Finish-out from a dry-in shell with slab | $100 – $150 |
| Finish-out from a bare shell (includes slab) | $115 – $165 |
| Shop side finished from a bare shell (slab, insulation, lights, sub-panel; doors already in) | $15 – $30 |
Those bands, added to a shell at $45–$65 per square foot, land at roughly the turnkey figures of $160–$230 for living area and $55–$80 for finished shop. The cost guide has the lines.
The lender and the appraiser
If the shell was paid for in cash and the finish-out is financed, the lender will treat the project as construction and want draws against inspections; if the county does no inspections (Warren, Lincoln), the lender's inspector does. The appraisal at the end needs the building to read as a house — living space dominant, finished to a standard a comparable sale supports. See financing and appraisal.
Not ready to talk yet?
Start with the planning layer: the complete St. Louis barndominium guide and insulation and condensation, which is the chapter that decides whether a finish-out succeeds.
Frequently asked questions
My shell came from a kit company. Will you finish it? Yes, after the four checks above. If the county needs an engineer's letter on the structure, we arrange it.
Can you finish just the living side and leave the shop bare? Yes. The shop still needs enough insulation to control condensation if it is conditioned at all.
How long does a finish-out take? As a planning assumption, three to six months for a 1,500–2,500-square-foot living area, longer in the code counties during inspection-heavy seasons.
Can I do some of the work myself? Yes, with the scope split in writing. Owner-done work is still inspected in the code counties, and the lender's draw schedule has to allow for it.