Section 179D Commercial Building Energy Deduction 2026: How Much Can You Claim?
Section 179D deduction amounts in 2026
| Energy savings achieved | Standard deduction ($/sq ft) | Prevailing wage bonus ($/sq ft) |
|---|---|---|
| 25% energy savings (minimum threshold) | $0.50 | $2.50 |
| 50% energy savings | $1.00 | $5.00 |
| 100% energy savings (maximum) | $2.00 | Not applicable (standard max) |
| Maximum with prevailing wage compliance | — | $5.65 (inflation-adjusted) |
The $5.65/sq ft maximum applies when both the 50% energy savings threshold and prevailing wage/apprenticeship requirements are met. This number is adjusted annually for inflation by the IRS.
What is Section 179D?
Section 179D of the Internal Revenue Code provides a tax deduction for energy-efficient commercial buildings and certain multifamily residential buildings. The Inflation Reduction Act (IRA) of 2022 significantly expanded the deduction, raising the maximum from $1.80/sq ft to $5.00/sq ft (later inflation-adjusted to $5.65/sq ft for 2026), and made the deduction available on a recurring basis — not just once per building.
The deduction applies to three building systems:
- Interior lighting systems
- HVAC and hot water systems
- Building envelope (insulation, windows, doors, roof)
All three systems can qualify together (whole building approach) or separately (partial qualification). The partial qualification allows a deduction of up to one-third of the maximum rate per system.
Who qualifies for Section 179D in 2026?
Two categories of taxpayers can claim Section 179D:
Building owners (standard)
Any owner of a commercial building placed in service after December 31, 2022, that meets the energy efficiency requirements qualifies. This includes:
- Office buildings, retail, industrial, warehouses
- Hotels and hospitality
- Multifamily residential buildings (4+ stories above grade)
- Mixed-use buildings with substantial commercial square footage
Designers of government-owned buildings (special allocation)
For tax-exempt entities (federal, state, local government buildings; tribal buildings; nonprofits), the deduction can be allocated to the designer — the architect, engineer, contractor, or energy services company primarily responsible for designing the improvements. This is a unique provision that makes 179D valuable to design and construction firms working on public buildings.
Energy savings requirement: the 25% threshold
To qualify for the base 179D deduction, the building must achieve at least 25% energy cost savings compared to a reference building that meets ASHRAE Standard 90.1 (the version in effect 2 years before the building was placed in service). For 2026, the relevant standard is typically ASHRAE 90.1-2019.
The energy savings percentage is calculated using IRS-approved software (EnergyPlus, eQUEST, DesignBuilder, or similar). A licensed engineer or energy modeler must certify the results. The energy model compares:
- Annual energy costs of the proposed design
- Annual energy costs of a reference building under ASHRAE 90.1
Deduction scales linearly between 25% and 50% energy savings. Above 50%, the standard rate stays at $1.00/sq ft; the prevailing wage multiplier (5x) applies on top.
The prevailing wage bonus: 5× multiplier
The IRA introduced a 5× multiplier on the base deduction for projects where the construction workers are paid prevailing wages as defined under the Davis-Bacon Act. For 2026:
- Base deduction at 50% savings: $1.00/sq ft
- With prevailing wage compliance: $5.00/sq ft (× inflation adjustment = ~$5.65/sq ft)
Prevailing wage requirements apply to all laborers and mechanics employed in construction, alteration, or repair work for the qualifying improvements. Compliance must be documented with certified payroll records. If you fail to meet prevailing wage requirements, you can correct the shortfall by paying back wages plus interest and a penalty — but catching deficiencies before filing is much easier.
How to claim Section 179D: the process
- Commission an energy model — Hire a qualified energy modeler using IRS-approved software to calculate the energy savings percentage vs ASHRAE 90.1 baseline.
- Get a qualified certification — A licensed engineer or contractor must certify the energy savings calculation. The certifier cannot be the building owner or a related party.
- Document prevailing wage compliance (if claiming the bonus) — Collect certified payroll records from all contractors and subcontractors for the project.
- Deduct on your tax return — Claim the deduction on Form 3115 (change in accounting method) or as a current-year deduction on your business tax return. The deduction reduces taxable income dollar for dollar.
- Keep records for at least 3 years — The energy model certification, payroll records, and building documentation should be retained in case of IRS review.
179D vs other commercial energy incentives
| Incentive | Type | Commercial buildings? | Max benefit |
|---|---|---|---|
| Section 179D | Deduction | Yes | $5.65/sq ft |
| Section 48 Investment Tax Credit | Tax credit | Yes (solar, storage) | 30–50% of project cost |
| Section 45L New Energy Efficient Home Credit | Tax credit | Multifamily (low-rise) | $2,500–$5,000/unit |
| Cost segregation | Accelerated depreciation | Yes | Varies (15-yr components) |
| PACE financing | Financing (not tax) | Yes | 100% project financing |
Section 179D can be stacked with Section 48 (solar/storage ITC) on the same building. The 179D deduction covers the building envelope and HVAC/lighting; the 48 ITC covers the solar installation. They are complementary, not mutually exclusive.
Example calculation: office building retrofit
Scenario: 50,000 sq ft office building, HVAC and lighting retrofit achieving 48% energy savings, with prevailing wage compliance.
- Energy savings: 48% → deduction rate interpolated between $0.50/sq ft (25%) and $5.00/sq ft (50%) = ~$4.84/sq ft
- Building area: 50,000 sq ft
- Total deduction: 50,000 × $4.84 = $242,000
- Tax savings (at 21% corporate rate): ~$50,820
If the same project had achieved exactly 50% savings: 50,000 × $5.65 = $282,500 deduction → ~$59,325 in tax savings.