Key Points
- Mixed-use properties contain both residential (27.5-year) and commercial (39-year) components—cost segregation applies to both
- The residential/commercial split is typically based on relative square footage
- Shared building systems (roof, foundation, HVAC, elevator) are allocated proportionally between uses
- Combined reclassification rates of 22–32% of depreciable basis are typical, depending on the commercial component type
A three-story building with street-level retail and apartments above. An old warehouse converted to office space on the first floor and loft apartments on the upper floors. A small-town Main Street building with a restaurant downstairs and two rental units upstairs.
Mixed-use properties are everywhere, and they present an interesting cost segregation scenario: the building contains components subject to two different default depreciation schedules. The residential portion defaults to 27.5 years under MACRS. The commercial portion defaults to 39 years. Cost segregation reclassifies qualifying components from both portions into shorter recovery periods—5-year personal property, 7-year property, and 15-year land improvements.
The mechanics are a bit more involved than a single-use property, but the economics are often better. Commercial components tend to have higher reclassification rates, and the longer 39-year default means each reclassified dollar moves further up the depreciation timeline.
What Qualifies as Mixed-Use
For cost segregation purposes, a mixed-use property is any single building (or set of buildings on one parcel) that contains both residential and non-residential components. The IRS classifies residential rental property as any building where 80% or more of the gross rental income comes from dwelling units. If the residential portion falls below that 80% threshold, the entire building is classified as non-residential (39-year property) under IRC §168(e)(2).
In practice, most mixed-use buildings don't hit the 80% residential threshold because the commercial space generates substantial rent. The result: the building is technically classified as 39-year property for default depreciation, but the cost segregation study still identifies and separates the residential and commercial components for accurate classification of shorter-life assets.
This is important because it means your CPA needs to understand how the building is classified for default depreciation purposes before the cost seg study is layered on top. The study itself handles the component-level analysis; the default classification determines the starting point. For a thorough explanation of the underlying methodology, see our guide to cost segregation.
How the Residential/Commercial Allocation Works
The first step in a mixed-use cost segregation study is splitting the building into its residential and commercial portions. This allocation determines how shared building systems are distributed and which default recovery period applies to each component group.
Typical Mixed-Use Building — Allocation by Square Footage
Square footage is the most common allocation method. If the commercial space occupies 4,000 SF of a 12,000 SF building, the commercial allocation is 33%. Some practitioners use relative rental income or relative assessed value, but square footage is the most straightforward and defensible approach for most properties.
Shared building systems—roof, foundation, structural framing, main HVAC distribution, elevators, fire suppression, and common-area finishes—are allocated proportionally. If the commercial space is 33% of the building, it receives 33% of the shared system costs. Each portion then receives its own 5-year, 7-year, and 15-year classifications based on component analysis.
Dedicated components are assigned entirely to one use. The restaurant's commercial kitchen equipment, exhaust hoods, and grease traps are 100% commercial. The apartment kitchen cabinets, bathroom fixtures, and unit-level flooring are 100% residential. The cost seg study classifies these within their respective recovery periods.
Common Mixed-Use Configurations
The most common mixed-use format. Ground-floor retail (one or multiple tenants) with 2–20+ apartments above. The retail component often produces 32–35% reclassification (storefront systems, specialty lighting, tenant partition walls, signage), while the residential component tracks standard multifamily benchmarks at 17–19%. Combined, these properties typically see 22–28% of total depreciable basis reclassified. See our retail cost seg page and multifamily page for type-specific detail.
Professional office space (law firms, accounting practices, coworking) on lower floors with residential units above. Office components—specialty electrical, data infrastructure, raised flooring, built-in cabinetry—produce 28–29% reclassification. The residential portion adds its own accelerated components. See our office cost seg page for detail on what drives the office reclassification rate.
Restaurant or food service space on the ground floor with residential above. Restaurants produce some of the highest reclassification rates in commercial (33–35%) because of commercial kitchen equipment, walk-in coolers, exhaust systems, and specialty plumbing. This configuration often produces the best combined cost seg results of any mixed-use format.
Units designed with ground-floor commercial or studio space and upper-level living quarters, often owned by the same person. Each unit has both a commercial and residential component. The allocation is typically 40–60% commercial depending on the configuration. These are less common but increasingly popular in urban infill developments.
A Worked Example
Consider a $1.8M mixed-use building in Austin, TX: 3,500 SF of ground-floor restaurant space and 5,500 SF of second- and third-floor apartments (four 2BR units). Total building is 9,000 SF.
Austin, TX — Restaurant + 4 Apartments
The restaurant component's 34% reclassification rate pulls the combined number well above what the residential portion would produce on its own. That $132,380 in estimated federal tax savings on a $1,495 study cost represents an 88:1 return.
100% bonus depreciation is permanent. Under the One Big Beautiful Bill Act (signed July 2025), all property placed in service in 2025 or later qualifies for 100% first-year bonus depreciation on reclassified components. There is no phase-down schedule. Both the residential and commercial reclassified assets in a mixed-use study can be fully deducted in Year 1. See our analysis of what these reclassification rates mean in dollar terms.
Frequently Asked Questions
Yes. Mixed-use properties are strong candidates for cost segregation because they contain both residential and commercial components, each with qualifying short-life assets. The study produces a unified report covering both portions of the building, with each component classified into the appropriate MACRS recovery period.
The most common method is relative square footage. If 40% of the building is commercial and 60% is residential, shared systems (roof, foundation, main HVAC, common areas) are allocated 40/60 between the two uses. Dedicated components—restaurant equipment, apartment fixtures—are assigned entirely to their respective use. Some practitioners use relative rental income or assessed value, but square footage is the most straightforward and widely accepted approach.
Typically yes, especially when the commercial use involves significant buildout (restaurants, medical offices, specialty retail). These spaces produce 30–35% reclassification rates compared to 17–19% for standard residential. However, both portions benefit from cost segregation. The residential component has a shorter default period (27.5 vs. 39 years), so while the reclassification percentage is lower, the underlying depreciation schedule is already faster.