Strategic Tax Planning for Mixed-Use Buildings

Unlocking Value Through Cost Segregation and 179D 

Mixed-use developments, properties that blend commercial and residential spaces, are now a defining feature of modern urban and suburban real estate. From retail and office space on the lower floors to apartments or condos above, they offer income diversity, convenience, and long-term value. But behind their architectural appeal is a tax planning challenge that requires precision and foresight. 

Due to the combination of property types and systems serving multiple uses, mixed-use buildings demand strategic planning, particularly in how depreciation, cost recovery, and energy incentives are applied. Cost segregation is the linchpin strategy here, and with recent tax legislation (the One Big Beautiful Bill or “OBBB”) reinstating 100% bonus depreciation, there’s even more opportunity to unlock immediate tax benefits, if executed properly. 

Understanding the Landscape: Why Mixed-Use Demands More 

Unlike single-use buildings, mixed-use projects must be divided between residential and nonresidential components. Shared infrastructure, such as HVAC, elevators, and lighting, must be thoughtfully allocated, and tax rules differ depending on use: 

• • Residential rental property: 27.5-year MACRS 

• • Nonresidential property: 39-year MACRS 

• • Personal property & land improvements: 5, 7, or 15 years 

• • Qualified Improvement Property (QIP): 15-year MACRS (interior of nonresidential space only) 

That mix can complicate bonus eligibility, QIP treatment, and the application of the §179D energy deduction. The IRS requires clear, reasonable, and supportable allocation methods between the uses, making documentation and planning critical. 

Cost Segregation as the Strategic Foundation 

Cost segregation reclassifies certain components of a building from 27.5- or 39-year lives to shorter-lived categories, making them eligible for faster depreciation. Considering the OBBB, this means immediate 100% expensing for eligible assets placed in service through 2025. In mixed-use developments, cost segregation must go a step further, not only identifying assets but assigning them appropriately between residential and commercial use. 

A properly executed mixed-use cost segregation study will: 

• • Identify shared and exclusive-use assets 

• • Allocate shared systems by square footage, usage, or engineering 

• • Break down improvements by space type 

• • Tag commercial interiors for QIP eligibility 

• • Document the logic behind every allocation for audit support 

The reward? Front-loaded deductions that significantly boost year-one cash flow. 

Allocation Methods: Getting It Right 

There is no one-size-fits-all allocation method, but the IRS expects consistency, reasonableness, and support. Common strategies include: 

1. 1. Square Footage: Simple and common for vertical mixed-use, but may not reflect cost intensity. 

2. 2. Actual Costs: When detailed invoices exist, this method gives the strongest audit trail. 

3. 3. Valuation-Based Allocation: Ties costs to relative value, especially useful when commercial space has higher build-out or revenue. 

4. 4. Engineering-Based Allocation: Particularly effective for shared systems like central HVAC or elevators. 

Often, the best studies blend multiple methods, square footage for some items, engineering-based for others, to ensure a defensible position. 

Bonus Depreciation: Back to 100% Under OBBB 

Thanks to the One Big Beautiful Bill, 100% bonus depreciation is back through the end of 2025 and applies to: 

• • Personal property (5- or 7-year) 

• • Land improvements (15-year) 

• • Qualified Improvement Property (15-year, nonresidential interior only) 

Residential improvements, even if identical to commercial, do not qualify for QIP or bonus depreciation unless they meet the separate requirements for short-lived personal property. Proper asset tagging through cost segregation ensures that every qualifying dollar is captured and depreciated immediately. 

§179D: The Enhanced Energy Deduction for Commercial Space 

The One Big Beautiful Bill (OBBB) extended and enhanced the §179D energy-efficient commercial building deduction, offering both immediate opportunity and a looming deadline. 

Key highlights: 

• • Deduction of up to $5.65 per square foot (2024, inflation-adjusted) 

• • Bonus rates available when prevailing wage and apprenticeship requirements are met 

• • Expanded eligibility for designers of tax-exempt buildings (e.g., architects, engineers, contractors) 

For mixed-use buildings, strategic application is critical: 

• • Only the commercial portion of the building qualifies for §179D 

• • Eligible improvements include: 

• • Interior lighting 

• • HVAC and hot water systems 

• • Building envelope upgrades (e.g., insulation, windows, roofing) 

• • Applicable to both new construction and renovations 

• • The deduction can be claimed by the building owner or allocated to designers in tax-exempt projects 

Importantly, under OBBB, §179D is set to sunset after 2032 unless extended again, meaning: 

• • Projects completed and placed in service before 2033 remain eligible 

• • With rising energy standards and increasing labor compliance requirements, early planning will be key to qualifying at maximum value 

Pairing a cost segregation study with an energy model allows building owners to: 

• • Accelerate depreciation under MACRS for systems like HVAC and lighting 

• • Claim the §179D deduction for the same systems — unlocking stacked benefits in the commercial portion of a mixed-use development 

For developers and advisors, this makes §179D an essential part of any energy or renovation strategy — but the window is not indefinite. 

Real-World Example: Integrated Tax Strategy in Action 

Scenario: A developer completes a $22 million mixed-use project in 2024: 

• • 40% commercial (ground + second floors) 

• • 60% residential (upper floors) 

• • Shared systems throughout 

• • $3 million invested in upgrading the commercial interiors 

Strategy: 

• • Cost segregation study identifies $6.4 million in 5-, 7-, and 15-year assets. 

• • Commercial portion (40%) qualifies for 100% bonus depreciation = $2.56 million immediate deduction. 

• • Commercial interior improvements qualify as QIP = another $3 million fully deducted under bonus rules. 

• • Lighting and HVAC systems meet energy standards = $180,000 §179D deduction. 

Total year-one tax benefit: Over $5.7 million in accelerated deductions and incentives. 

Result: Increased cash flow, reduced taxable income, and a defensible position supported by clear allocations and technical documentation. 

Key Takeaways for CPAs, Advisors, and Developers 

Pre-project planning is critical. Cost segregation and §179D strategies are best implemented when documentation is gathered early, not after the project is complete. 

Allocation matters. Don’t let shared systems and mixed-use functions create audit risk. Use engineering-based or invoice-supported methods where possible. 

QIP and §179D don’t overlap. Know where each applies and use both strategically. 

OBBB timing is everything. With 100% bonus depreciation available only through 2025 (unless extended again), the next 18 months offer a rare opportunity to stack savings. 

Partner with experts. Cost segregation in mixed-use environments is not for the untrained. Engage a provider that understands allocations, energy deductions, and audit documentation. 

Thinking Ahead? 

If you or your client is planning a mixed-use development, renovation, or commercial improvement, especially one going live before 2026, now is the time to explore strategic tax planning. With bonus depreciation fully restored and enhanced §179D incentives in play, the window for maximizing value is wide open. 

Let’s talk before your next project goes live. We can help evaluate eligibility, design the optimal strategy, and support your team in implementation. 

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