The $5.65-Per-Square-Foot Deduction Most Commercial Building Owners Have Never Claimed

The Deduction That Arrived Quietly

If you own a commercial building — an office, a warehouse, a retail space, a medical facility, an apartment building with five or more units — and you have made improvements to the lighting, HVAC system, or building envelope in the last several years, there is a meaningful chance you are sitting on an unclaimed federal tax deduction worth tens of thousands of dollars.

It is called Section 179-D. Most building owners have never heard of it. Many CPAs who learned tax law before 2023 know the old version of it — a modest, temporary credit that expired and got renewed every year. What exists today, after the Inflation Reduction Act made it permanent and tripled the deduction amount, is a different program entirely.

We are not talking about a small line item. On a 20,000 square foot building that qualifies at the full rate, this is a deduction worth over $113,000. On a 50,000 square foot building, it is more than $280,000. These are real numbers, and they are going unclaimed every year because nobody is asking the right questions.

What Section 179-D Actually Is

Section 179-D is a deduction under the Internal Revenue Code for energy-efficient improvements made to commercial buildings located in the United States. It was originally created as part of the Energy Policy Act of 2005, spent years as a temporary provision that Congress renewed intermittently, and was finally made permanent — and dramatically expanded — by the Inflation Reduction Act of 2022, effective for tax years beginning in 2023.

The basic structure is straightforward. If you own a commercial building and make qualifying improvements to one or more of three building systems, and those improvements reduce the building's energy usage below a federally defined benchmark, you can deduct a specified dollar amount per square foot of the improved space in the year those improvements are placed in service.

The maximum deduction for 2026 is $5.65 per square foot, adjusted for inflation annually. You do not have to guess whether you qualify. There is a defined certification process, a defined energy standard, and a defined dollar amount. The math is concrete once someone runs it.

The Three Systems That Unlock the Deduction

Section 179-D applies when qualifying energy improvements are made to any of the following three building systems:

You do not need to have improved all three systems to qualify. A lighting upgrade alone can generate a deduction. An HVAC replacement alone can generate a deduction. The deduction scales with how much of the building was improved and by how much the improvement reduced energy usage — but the bar to qualify is lower than most people assume.

If you have done any meaningful energy-related work on your commercial building in the last several years and have not had a 179-D analysis run, there is a real chance money has been left on the table.

The Math: What It Is Actually Worth

The deduction amount depends on two factors: the square footage of the improved space and the percentage reduction in energy cost achieved relative to the ASHRAE 90.1 reference standard. The minimum threshold to qualify is a 25% reduction. The maximum deduction is achieved at a 50% or greater reduction.

These figures assume the full deduction rate, which requires meeting prevailing wage and apprenticeship requirements under the IRA. For improvements that do not meet those thresholds, the base deduction is one-fifth of the full amount — still meaningful, but significantly lower. A 179-D analysis will tell you exactly which rate applies to your project.

One important note: 179-D is a deduction, not a tax credit. It reduces your taxable income rather than reducing your tax bill dollar for dollar. The actual tax savings depend on your effective rate. But on a meaningful property, those savings are substantial either way.

A few years ago, at a banking and economics conference, a bank CEO made an offhand comment that stuck. He said that if a commercial building owner was not taking advantage of the 179-D deduction, his institution would come in, fund the qualifying energy upgrades entirely, file the certification, claim the deduction, and split the tax savings with the building owner. No cost to the owner. Pure upside in exchange for access to a credit the owner was not using anyway.

We are not naming the institution and we are not endorsing that particular arrangement. But the point stands: sophisticated financial players are actively hunting for unclaimed 179-D opportunities. They are building entire programs around a deduction that most building owners have never heard of. When institutional money is willing to front capital just to get a share of a tax benefit you are leaving on the table, that tells you something about how real the numbers are.

What the Inflation Reduction Act Changed

Before 2023, Section 179-D was a known-but-limited provision. The maximum deduction was $1.80 per square foot. It expired and required congressional action to renew. Many tax professionals treated it as an afterthought — technically available, practically inconsistent, and not worth building a strategy around.

The Inflation Reduction Act changed all of that in three significant ways:

• The deduction was tripled — the base maximum went from $1.80 to $5.00 per square foot, inflation-adjusted annually (currently $5.65 for 2026).
• It was made permanent — no more annual extensions, no more uncertainty about whether the provision will exist next year. Building owners can now plan around it with confidence.
• The energy standard was updated — the benchmark shifted to the most recent version of ASHRAE 90.1 published at least four years before the property is placed in service.

The result is a program that is more valuable, more stable, and more applicable to modern construction and renovation than what existed before. And because most tax professionals learned about 179-D in its earlier, limited form, a significant number of qualifying projects are still going unanalyzed.

The Rule Almost Nobody Knows: Tax-Exempt Buildings

The Certification Requirement — Why You Cannot Self-Certify

Section 179-D requires a formal certification performed by a qualified engineer or contractor using IRS-approved energy modeling software. This is not a form you fill out on your own or a checkbox in your tax return. It is a technical analysis that models the energy performance of the building and verifies that the improvements meet the required threshold.

The certification needs to be completed before the deduction is claimed, and it needs to be done by someone who is qualified under the IRS definition — a licensed engineer or contractor in the jurisdiction where the building is located. The output is a signed certification document that becomes part of your tax records.

This requirement is one of the main reasons the deduction goes unclaimed. It is not that building owners are ineligible. It is that claiming the deduction requires an extra engagement that most CPAs are not equipped to perform and do not think to recommend.

How to Know If You Qualify

The qualifying question is not whether your building is new or recently built. Many older buildings have had lighting replacements, HVAC upgrades, or roof replacements that qualify under current standards. Improvements made in prior years can sometimes be captured through amended returns, depending on the specifics.

Ask yourself:

• Do you own a commercial building — office, warehouse, retail, medical, industrial, or multifamily with five or more units?
• Has there been any work done on the lighting, HVAC, or building envelope in the past three to five years?
• Has anyone ever run a Section 179-D analysis on the property?

If the answer to the first two is yes and the answer to the third is no, you have an open question worth answering. The analysis will either confirm there is a deduction available or tell you there is not. Either way, you will know.

We are not in the business of telling people they qualify when they do not. But we have seen enough of these analyses to know that qualifying improvements are far more common than most building owners realize — and that the deduction is large enough that the cost of not checking is almost always higher than the cost of finding out.