Section 179D lets architects, engineers, and design-build contractors take a federal tax deduction for energy-efficient work they perform on government and nonprofit buildings. Here is how it works, who qualifies, and why the window is closing.
Section 179D of the Internal Revenue Code creates a federal income tax deduction for installing energy-efficient property in commercial buildings. It is a deduction, not a credit, so it reduces taxable income rather than the tax itself.
The provision has been part of the tax code since 2005, but the Inflation Reduction Act of 2022 transformed it. The IRA lowered the qualification threshold from 50% energy savings to 25%, expanded the eligible building owners to include nonprofits and tribal governments, introduced a 5x multiplier for projects meeting prevailing wage and apprenticeship standards, and made the deduction permanent with inflation adjustments.
Then the One Big Beautiful Bill Act pulled it back. Signed July 4, 2025, OBBBA sunsets Section 179D for any property whose construction begins after June 30, 2026. Projects already underway or completed remain eligible, but the pipeline for new claims is closing.
The deduction flows to the person who creates the technical specifications for the energy-efficient property. Not the person who installs, repairs, or maintains it.
Building envelope design, overall energy strategy, and coordination of energy-efficient systems across the project.
MEP design for HVAC, lighting, and service water heating systems. Each system can have its own qualifying designer.
Firms that both design and construct, provided they hold the design contract and create the technical specifications.
Because 179D covers three distinct building systems, each can have its own designer. The architect might claim the envelope deduction while the MEP engineer claims the HVAC and lighting portions. The allocation is determined by the building owner and documented in the allocation letter. There is no requirement that one person take the entire deduction.
The IRA expanded the list of "specified tax-exempt entities" beyond government agencies. Any of these owners can pass the deduction to their designer:
The deduction scales with energy savings and multiplies by five if the project meets prevailing wage and apprenticeship (PW&A) requirements. For 2026, the inflation-adjusted maximums are:
The math is a sliding scale. At 25% energy cost savings, the base deduction is $0.59 per square foot, climbing by $0.02 for each additional percentage point of savings up to the cap at roughly 50%. Meet prevailing wage and apprenticeship rules and that entire scale multiplies by five.
The deduction lives or dies by its documentation file. Sloppy or unsupported filings draw scrutiny on Form 7205, the IRS's primary audit-targeting tool for 179D claims.
The building's total annual energy and power costs must be at least 25% below the ASHRAE Reference Standard 90.1 baseline for the applicable year. Greater savings unlock a larger per-square-foot deduction on a sliding scale up to roughly 50%.
A qualified third party runs an IRS-approved software simulation (eQUEST, EnergyPlus, Trane TRACE, or similar), comparing the building against the ASHRAE reference building. Self-certification voids the deduction.
The tax-exempt building owner signs a formal letter allocating the 179D deduction to the designer(s). The letter must identify the building, the designer, the system(s) covered, and the deduction amount. This is the legal instrument that transfers the deduction.
If pursuing the enhanced (5x) deduction, collect and retain certified payroll records and apprenticeship labor-hour logs. These cannot be assembled retroactively.
The designer attaches Form 7205 to their return, documenting the building, the energy modeling, the allocation, and the deduction claimed. The full certification and allocation file is retained but not submitted unless requested on exam.
OBBBA repealed Section 179D for property whose construction begins after June 30, 2026. That is not a "placed in service" deadline. It is a "beginning of construction" deadline, which means the rules for establishing that start matter.
The IRS recognizes two paths for beginning of construction. Either physical work of a significant nature begins on the project (the Physical Work Test), or the taxpayer incurs at least 5% of total project cost (the 5% Safe Harbor). Site clearing and grading alone do not count. For projects in the pipeline, the decision is straightforward: break ground or lock in at least 5% of cost before July 1, 2026.
Projects that begin construction before the deadline remain fully eligible, even if the building is not placed in service until years later. There is a continuity requirement, but the IRS has historically provided safe harbors of four to six years between beginning of construction and placed in service for energy incentives.
If you design energy-efficient buildings for government agencies, schools, hospitals, nonprofits, or tribal entities, there is a federal deduction, up to $5.94 per square foot, that you can claim on your own return for work you already performed. The provision sunsets for new projects starting after June 30, 2026. The look-back provision means prior years may still be in play. The documentation requirements are real, but the payoff scales with the size of the building, and very few eligible designers are claiming it.