Multifamily Cost Segregation Isn't Just 'Smaller Office': Why 5+ Unit Apartments Need Property-Specific Engineering

The multifamily depreciation arithmetic

Multifamily (5+ unit) properties operate under a different depreciation regime than commercial real estate. The structural component depreciates over 27.5 years under IRC §168(c) as residential rental property, not the 39 years that applies to nonresidential. The accelerated buckets identified through cost segregation — 5-year, 7-year, 15-year — sit on top of that 27.5-year baseline.

This produces three consequences that affect every multifamily cost-segregation study:

1. Lower headline reclassification percentages. Multifamily reclassifies in the 16-20% range vs commercial in the 24-32% range. The reason isn’t engineering — it’s that the multifamily 27.5-year structural class already absorbs components that would be in the 5/7/15-year bucket under a 39-year commercial schedule.

2. 27.5-year depreciation already runs faster than commercial structural. The “additional” benefit of cost segregation is the spread between 5/7/15-year accelerated depreciation and 27.5-year straight-line — a smaller spread than the same accelerated buckets vs 39-year structural.

3. Recapture treatment differs. The accelerated buckets are §1245 property (ordinary recapture). The 27.5-year residential structural is §1250, with the bulk taxed as unrecaptured §1250 gain at the 25% maximum rate.

The net of all three: multifamily cost segregation produces a smaller absolute benefit per dollar of basis than commercial cost segregation, but the IRR on the strategy is still typically positive given the 100% bonus depreciation available under OBBBA.

The 80% gross-rents test

The classification as “residential rental property” under IRC §168(e)(2)(A) requires that 80% or more of the gross rental income from the property be from dwelling units. This test:

• Applies on a building-by-building basis
• Is tested annually
• Determines whether the structural depreciates over 27.5 years (passes) or 39 years (fails)

For pure apartment buildings, the test is easy to satisfy — 100% of rent comes from dwelling units. For mixed-use buildings with ground-floor retail or commercial uses, the test can become marginal.

A building with 30 apartments generating $1.2M/year and ground-floor retail generating $400K/year has 75% from dwelling units — failing the 80% test, classified as nonresidential, structural depreciates over 39 years.

A building with 60 apartments at $1.8M and ground-floor retail at $400K has 81.8% from dwelling units — passing, structural at 27.5 years.

The single percentage point can mean significantly different depreciation profiles over a multi-year hold. Properties near the threshold need careful annual testing, and renovations that shift the ratio (adding retail, removing units) can change the classification.

What gets reclassified in multifamily

The engineering categories in a multifamily cost segregation study:

5-year personal property (Section 1245)

In-unit components (landlord-owned):

• Carpet, vinyl plank flooring, resilient flooring
• Cabinetry and millwork (when removable — typical apartment cabinets pass the §1.48-1(c) permanence test)
• Appliances: refrigerators, ranges, dishwashers, microwaves (when landlord-owned)
• Washers and dryers (when in-unit and landlord-owned)
• Window treatments
• Decorative lighting (pendants, accent fixtures)

Common-area amenities:

• Clubhouse buildout (carpet, decorative finishes, lighting)
• Fitness center equipment (when landlord-owned)
• Pool equipment (filters, pumps, heaters, chemical-feed systems, automated covers)
• Smart-home and IoT systems (smart locks, thermostats, keyless entry, package lockers)
• Office buildout in the leasing office

15-year land improvements (Section 1250 — but §1245 for recapture)

• Parking lots (asphalt, striping, curbs)
• Carports and covered parking (when not structurally attached to the building)
• Pool deck and pool surrounds (the pool shell itself is structural)
• Site lighting (parking lot poles, walkway lighting)
• Landscaping, irrigation, mulched beds
• Sidewalks, ADA paths, curb cuts
• Fencing, gates, perimeter security
• Outdoor amenities (BBQ pavilions, dog parks, pet washing stations)

27.5-year residential rental (Section 1250)

• Building shell, foundation, roof, structural framing
• Base building HVAC (central plants for buildings that have them; unit-level HVAC may be 5-year if removable)
• Structural plumbing service entrance
• Structural electrical service
• Permanent partition walls between units (demising walls)
• Elevators (always 27.5-year for residential rental)
• Permanent fire suppression infrastructure
• Pool shell, pool tile

Appliance ownership: the most consequential audit point

The single largest 5-year personal property category in multifamily is typically appliances — refrigerators, ranges, dishwashers, and in-unit washer/dryers. Across a 100-unit property, this can be $200K-$400K of basis at full 5-year depreciation with §168(k) bonus.

The audit question: does the landlord own the appliances?

If yes, they’re in the landlord’s depreciable basis and depreciate at 5 years.

If the appliances were purchased by the tenant (rare in market-rate rentals but common in some affordable-housing programs), they’re not in the landlord’s basis at all.

If the landlord provides appliances “as-is” but tenants are responsible for replacement, the depreciation treatment depends on the specific lease language and the practice at the property — the leasing agreement, the property’s capex history, and the typical lease language all matter.

Engineering documentation in the cost segregation report should specify the appliance ownership pattern based on lease review and capex records. This is the single most common cost-seg-on-multifamily audit point.

Pool and amenity classification

The pool is a case study in multifamily-specific component allocation. Three layers:

1. Pool shell, structural concrete, tile, perimeter walls — 27.5-year structural (Section 1250)
2. Pool deck, pool surrounds, perimeter paving — 15-year land improvement (Section 1250, but §1245 for recapture)
3. Pool equipment — pumps, filters, heaters, chemical-feed systems, automated covers — 5-year personal property (Section 1245)

A property’s pool basis can run $80K-$400K depending on size and amenity level. The split among the three classes determines how much of that basis is accelerated:

• A simple in-ground pool with basic equipment: ~$200K basis, ~$60K shell (27.5-yr), ~$80K deck (15-yr), ~$60K equipment (5-yr)
• A premium amenity pool with extensive deck, water features, and automated systems: ~$500K basis, ~$150K shell, ~$200K deck/water features, ~$150K equipment

The engineering documentation should photographically distinguish each layer. The mounting and connection detail of the equipment vs the structural pool shell is the basis for the classification.

Carports vs garages — a common misclassification

Carports and detached garage structures are 15-year land improvements when they meet two tests:

1. Detached from the main building — independent foundation, not structurally connected
2. Not subject to a separately-stated lease as a permanent improvement — the carport rental, if any, is part of the unit’s amenity, not a separate real-estate lease

Attached garages — those structurally connected to the building, sharing walls or foundation — follow the building’s 27.5-year class.

The classification is frequently misapplied. Some studies treat all parking-related structures as 15-year regardless of attachment; others treat detached carports as 27.5-year structural. The engineering documentation should photograph the connection detail and state the classification rationale.

Smart-home and IoT — newer 5-year category

Multifamily acquisitions in the past 5-7 years increasingly include smart-home infrastructure:

• Keyless entry / smart locks
• Smart thermostats (Nest, Ecobee, similar)
• Smart leak detection systems
• IP-based intercom and access control
• Package lockers
• Centralized leak and HVAC monitoring

All of these are 5-year personal property under §1245 — they’re functional equipment, removable, not integral to the building structure. For a property with $50K-$150K of smart-home infrastructure, the cost-seg classification matters.

Engineering documentation should list the smart-home components individually with cost allocation against the construction or capex records.

Engineering specifics — multifamily structural efficiency

The Cost Seg Smart engineering methodology applies two multifamily-specific factors that distinguish multifamily studies from generic commercial templates:

1. Multifamily structural efficiency factor (0.90): Multifamily buildings allocate less of total basis to structural envelope than equivalent-square-footage commercial buildings because of the repetitive unit layout. The 0.90 factor adjusts the structural-vs-finish ratio accordingly.

2. Shared-system discount (0.82): Multifamily shared systems (single elevator serving multiple units, central plant HVAC serving the whole building, shared corridor lighting) are allocated across all units, reducing the per-unit shared-system basis. The 0.82 discount factor reflects this.

These factors typically aren’t applied in generic commercial cost-segregation templates. Multifamily studies run through a commercial template without these adjustments tend to overstate the reclassification percentage by 2-4 percentage points — producing positions that may fail at audit when the IRS examines the cost allocation.

§469 passive activity interaction

Multifamily losses are subject to the §469 passive activity rules. For multifamily investors, the relevant exceptions:

1. Real Estate Professional Status (REPS) under §469(c)(7): typically the path for full-time multifamily operators who satisfy both the 50% personal-service test and the 750-hour test in real property trades or businesses.

2. Short-term rental ≤7-day average: not generally applicable to traditional multifamily (which has long-term leases), but applies to property operating in furnished-rental or extended-stay formats with average customer use ≤7 days.

3. Active participation $25,000 allowance under §469(i): phased out at $150K of modified AGI. For most multifamily investors above the phase-out, this is not a meaningful path.

For high-income multifamily investors not qualifying for REPS, cost-segregation-generated losses are suspended under §469 and carry forward until passive income or disposition releases them. The strategy still works — it’s just deferred.

Disposition: §1245 vs §1250 split

At sale, the bifurcated recapture treatment applies:

• 5-year and 7-year reclassified components: §1245 recapture, ordinary income up to 37%
• 15-year land improvements (including parking, pool deck, site work): §1245 by reference under §1245(a)(3)(D), full ordinary recapture
• 27.5-year residential rental structural: §1250 — but §1250 ordinary recapture is zero under MACRS (straight-line), so the bulk taxed as unrecaptured §1250 gain at the 25% maximum rate
• Land: capital gain at 20% top federal long-term rate

The bracket modeling at disposition determines the net of cost segregation. For high-bracket multifamily holders selling after a multi-year hold, the §1245 recapture on the cost-seg-reclassified components can claw back a meaningful portion of the year-1 deferral benefit.

Common errors

1. Applying commercial cost-seg ratios to multifamily. Multifamily property profiles are structurally different from commercial. Templates that don’t adjust the structural-efficiency and shared-system factors overstate the reclassification.

2. Misclassifying tenant-owned appliances. Verifying ownership through lease review and capex records is structural to the audit defense. A study that classifies tenant-owned appliances as landlord-depreciable is recharacterized at audit.

3. Failing the 80% gross-rents test without realizing it. Mixed-use multifamily-plus-retail buildings near the 80% threshold need annual testing. The classification can flip year to year.

4. Treating QIP as available for multifamily. QIP under IRC §168(e)(6) is nonresidential only. Interior improvements to residential rental property are not QIP. Multifamily renovations follow standard 27.5-year MACRS (with cost-segregation breaking out the accelerated buckets).

5. Cost segregation on LIHTC property without coordination. Low-Income Housing Tax Credit properties have eligible basis calculations that interact with cost segregation. The cost-seg-reduced depreciable basis can affect the LIHTC calculation. Coordination with the LIHTC tax counsel is required.

Modeling cost segregation on a specific multifamily property? The reclassification percentage, the §469 passive activity treatment, and the disposition modeling all depend on property-specific facts. A property-specific engineered analysis shows the multifamily-adjusted reclass percentage and the per-property year-1 bonus depreciation.