Section 179D is a federal tax deduction for energy-efficient commercial building improvements. Building owners (and, in some cases, designers of government-owned buildings) can claim up to $5.00 per square foot for qualifying upgrades to lighting, HVAC, and the building envelope.
How it works
To qualify, the building improvements must reduce total annual energy costs by at least 25% (compared to a reference building meeting ASHRAE Standard 90.1). The deduction sliding scale runs from $0.50/sqft (25% energy savings) up to $5.00/sqft (50%+ savings, with prevailing-wage compliance).
Interaction with cost segregation
Cost segregation reclassifies the basis you depreciate. Section 179D is a separate deduction layered on top — claimed in the year of placed-in-service for the energy-efficient improvements. The two strategies are complementary, not competing, and many large commercial owners stack both.
Who should care
Owners of commercial buildings 50,000+ sqft where you've invested in efficient HVAC, LED lighting, or a high-performance building envelope. The deduction is most material on new construction or substantial renovations. For typical residential or small-commercial properties, the §179D math rarely justifies the certification cost.