Commercial Interior Fit-Out Contractors

Commercial interior fit-out is the process of transforming a bare or previously occupied commercial shell space into a fully functional, code-compliant interior environment. This page covers the definition of fit-out work, how the construction sequence operates, the business contexts in which fit-out contracts are awarded, and the decision factors that distinguish fit-out from adjacent project types. Understanding these boundaries helps property owners, tenants, and project teams engage the right commercial contractor services categories from the outset.

Definition and scope

A commercial interior fit-out refers to the installation of all interior building components—partitions, ceilings, mechanical distribution, electrical systems, finishes, and fixtures—within a structurally complete shell. The shell itself (core structure, exterior envelope, primary mechanical risers) is excluded from fit-out scope. Fit-out scope begins where the base building ends.

The Construction Specifications Institute (CSI) MasterFormat, which organizes construction work into numbered divisions, places the bulk of fit-out trade work in Divisions 06 through 12 (wood and plastics, thermal and moisture protection, openings, finishes, specialties, and equipment) and Divisions 21 through 28 (fire suppression, plumbing, HVAC, electrical, communications, and electronic safety) as distributed branch work within the tenant space. This structure is distinct from the primary mechanical, electrical, and plumbing (MEP) infrastructure covered under base building permits.

Fit-out contractors typically hold general contractor licenses and self-perform or subcontract commercial electrical contractor services, commercial plumbing contractor services, and commercial HVAC contractor services as coordinated packages. The scope of a fit-out engagement is formally bounded by the lease agreement, which specifies the "landlord work" versus "tenant work" demarcation line.

How it works

A commercial interior fit-out follows a defined sequence of phases:

1. Pre-construction and design coordination — The fit-out contractor reviews base building drawings, lease exhibits, and landlord design criteria. Coordination with the structural engineer is required if the fit-out includes slab penetrations, mezzanines, or heavy floor loads. This phase often overlaps with pre-construction services commercial deliverables such as constructability reviews and preliminary cost models.

2. Permit acquisition — Interior fit-out work requires a separate tenant improvement permit in most US jurisdictions, even when the base building certificate of occupancy is already issued. The permit set must demonstrate compliance with the applicable edition of the International Building Code (IBC) and local amendments, including egress path calculations, occupancy load analysis, and accessibility under the Americans with Disabilities Act (ADA), enforced by the US Department of Justice under 28 CFR Part 36.

3. Demolition and rough-in — If the space was previously occupied, selective demolition removes existing finishes, mechanical components, and partitions. New MEP rough-in—conduit, ductwork, and piping—is installed in the ceiling plenum and walls before any finish surfaces close the cavity.

4. Framing and drywall — Metal stud framing defines the partition layout. Gypsum board assemblies are selected to meet fire-resistance ratings specified in the IBC, which requires one-hour or two-hour rated assemblies at corridor and separation walls depending on occupancy classification.

5. Finish trades — Commercial flooring contractor services and commercial painting contractor services execute in sequence after MEP inspections pass. Millwork, ceilings, and specialty finishes follow.

6. Final inspections and occupancy — The authority having jurisdiction (AHJ) conducts life safety, MEP, and accessibility inspections before issuing a certificate of occupancy or a tenant improvement sign-off.

Common scenarios

Fit-out contracts arise in four primary commercial contexts:

New shell lease (vanilla shell or warm shell) — A landlord delivers a space with concrete floors, exposed ceilings, and stubbed MEP connections. The tenant funds and directs all interior construction. Tenant improvement (TI) allowances—expressed as a dollar-per-square-foot figure in the lease—offset a portion of tenant construction cost. Market TI allowances vary significantly by submarket and lease term; the CoStar Group tracks average TI allowances by metropolitan area in its leasing analytics database.

Second-generation space — An existing tenant build-out is reused with modifications. Selective demolition costs are lower, but existing conditions may impose constraints on the new layout, particularly around fixed MEP penetrations. Commercial renovation and remodeling contractors with fit-out experience are equipped to assess existing condition value versus replacement cost.

Owner-occupied build-out — A property owner constructs interior improvements for their own occupancy. This scenario removes the lease-demarcation variable but retains all permitting and code requirements.

Healthcare or specialized occupancy — Fit-out for medical office, outpatient clinic, or laboratory space introduces supplemental requirements under the Facility Guidelines Institute (FGI) Guidelines for Design and Construction of Outpatient Facilities, adopted by 42 US states as of the FGI's published adoption map. These environments also engage healthcare facility contractor services specialization due to infection control, plumbing fixture ratios, and medical gas requirements.

Decision boundaries

Fit-out vs. tenant improvement (TI) — The terms are often used interchangeably, but a distinction exists in some lease structures. Tenant improvement (TI) refers specifically to landlord-funded or landlord-managed construction work. Fit-out is the broader construction category, regardless of funding source. Commercial tenant improvement contractors are a subset of the fit-out contractor market.

Fit-out vs. base building — Base building contractors handle the structural frame, core MEP infrastructure, and exterior envelope. Fit-out contractors take over at the demised space boundary. Engaging a general contractors commercial services firm that performs both base and fit-out work under a single contract—common in design-build delivery—can reduce coordination risk but requires clearly defined scope exhibits in the contract.

Fit-out vs. renovation — Renovation implies modifying an existing occupied or functional interior, often while occupancy continues in adjacent areas. Fit-out implies constructing from a raw or cleared shell condition. The distinction affects phasing, temporary occupancy requirements, and infection/dust control protocols.

Contractor selection criteria — The commercial contractor selection criteria relevant to fit-out engagements weight sector-specific experience heavily. An office fit-out contractor's portfolio is not automatically transferable to retail or healthcare fit-out without supplemental competency in those regulatory environments.

References

• Construction Specifications Institute (CSI) MasterFormat — Division structure used to classify fit-out trade scope.
• International Building Code (IBC) — International Code Council — Occupancy classification, egress, and fire-resistance rating requirements applicable to interior fit-out permits.
• Americans with Disabilities Act (ADA) Standards for Accessible Design — US Department of Justice, 28 CFR Part 36 — Federal accessibility requirements enforced in all commercial tenant spaces.
• Facility Guidelines Institute (FGI) — Guidelines for Design and Construction of Outpatient Facilities — Standards governing fit-out of healthcare outpatient environments, adopted by 42 states.
• US Department of Justice — ADA Title III Overview — Enforcement framework for commercial facility accessibility compliance.