What is Section 179D? 

Section 179D is a federal tax deduction for installing qualifying energy-efficient systems in commercial buildings. It was created nearly 20 years ago to encourage investment in energy-saving building components like interior lighting, HVAC, and building envelope upgrades. In practice, 179D lets building owners (or certain designers) deduct a portion of their building improvement costs, reducing the building’s tax basis in exchange for an immediate write-off. This one-time deduction can be as high as $5.94 per square foot for energy-efficient buildings placed in service in recent years. (By contrast, it was capped at $1.80 per square foot in earlier years.) The exact deduction amount depends on the degree of energy savings achieved – at least 25% savings is required to claim anything, scaling up to a 50% energy cost reduction for the maximum deduction. Moreover, if a project meets certain labor standards (prevailing wage and apprenticeship requirements), the available deduction is roughly quintupled (from a max of $1.16/sqft up to $5.81/sqft in 2025). In short, 179D rewards you for building or retrofitting beyond standard energy code efficiency, aligning tax benefits with green building practices.

Historic Context

Section 179D was originally introduced by the Energy Policy Act of 2005 (often called “EPAct 2005”), initially allowing up to $1.80/sqft for qualifying projects. It started as a temporary incentive and went through several extensions over the years. Notably, Congress renewed 179D multiple times (e.g. via the 2017 tax act and 2019 legislation) until finally making it a permanent part of the tax code in late 2020. This permanence gave building owners and designers more certainty that energy-efficient projects could earn tax deductions going forward. The Inflation Reduction Act (IRA) of 2022 then brought major enhancements: effective 2023, IRA raised the deduction limits (from the old $1.80/sqft cap to a new $5.00+ per sqft framework) and expanded eligibility. For example, before IRA, only government-owned buildings could allocate 179D deductions to designers; after IRA, tax-exempt entities like nonprofits, schools, and tribes can also pass their deduction to the project’s designer (architects, engineers, contractors) since those entities don’t pay tax. IRA also allowed the same building to claim 179D more than once – essentially every 3 or 4 years – if additional energy-saving renovations are done. All these changes supercharged 179D’s value and scope starting in 2023.

Latest Developments

Most recently, the One Big Beautiful Bill Act (OBBBA), enacted July 4, 2025, introduced a new sunset date for 179D. Under OBBBA, projects must begin construction by June 30, 2026 to qualify for the deduction. (The actual placement in service can occur later, but the start date is key.) Any property whose construction starts after that date will not be eligible for 179D as the law stands. This effectively gives a limited window for taxpayers to take advantage of the incentive, injecting some urgency into project planning. It’s a notable shift because IRA had made 179D a long-term fixture, but OBBBA’s deadline means the incentive could expire for new projects unless Congress extends it again. In addition, OBBBA retained the higher deduction rates and other IRA rules in the meantime, but it reinforced the need to plan and act before the mid-2026 cutoff.

Who Can Claim the Deduction? 

There are two primary beneficiary groups for 179D: building owners and building designers. For commercial building owners who pay taxes, 179D works as a tax break for investing in energy-efficient systems – essentially a way to write off part of your construction costs immediately (we’ll discuss this “accelerated depreciation” effect in the next article). Owners of offices, warehouses, apartments (4+ stories), retail centers, and industrial facilities all commonly use 179D if they install qualifying lighting, HVAC, or envelope upgrades. Uniquely, Section 179D also incentivizes architects, engineers, and other designers: if you design a qualifying government or certain tax-exempt building, the building owner (who can’t use the deduction) can allocate the tax deduction to you as the designer. This means firms that design schools, libraries, city halls, university buildings, non-profit hospitals, etc., can receive a valuable deduction for their work, even though they don’t own the building. (An allocation letter from the owner is required to transfer the deduction.) This policy aims to reward the parties responsible for the energy-saving design features. In summary, owners of private commercial buildings and designers of public or non-profit buildings can both benefit from 179D in the right circumstances.

How Projects Qualify

To qualify for 179D, the project must involve improvements to the building’s interior lighting, HVAC/hot water systems, or building envelope that reduce the building’s annual energy usage by at least 25% compared to a baseline standard. The baseline is defined by ASHRAE Standard 90.1 (the model energy code) as of a certain date – for example, ASHRAE 90.1-2007 is the reference for projects started before 2027. An energy simulation (or an approved alternative method) must show the percentage savings, and greater savings yield a bigger deduction per square foot (capped at 50% savings). All this has to be verified and certified by a qualified professional, which we’ll cover later in this series. For now, the takeaway is: if you incorporate significant energy-efficient designs into a new building or retrofit, you could be looking at tens or even hundreds of thousands of dollars in tax deductions. For example, a 100,000 sq. ft. office building meeting the full efficiency criteria might earn over $500,000 in deductions (100k sqft × ~$5/sqft). Even partial improvements (e.g. just a lighting upgrade saving 25–30%) can qualify for a prorated deduction. The incentive has proven valuable enough that it’s now a routine consideration in commercial building projects. In upcoming articles, we’ll explore how to maximize these savings and navigate the technical requirements.