Federal Tax Incentive · IRC §179D

The §179D First-Year Deduction for Commercial Building Energy Systems

IRC §179D provides a first-year federal tax deduction of up to $5.94 per square foot for qualifying energy systems in commercial buildings. Rates significantly expanded under the Inflation Reduction Act of 2022. PE-certified in-house, coast to coast.

$5.94
Max per sq ft
2026 PWA Rate
3
Qualifying
Systems
3+ Yrs
Look-Back
Available
30 min
Eligibility Review
No Obligation
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What Is §179D

What Is the 179D Energy Deduction?

IRC Section 179D provides a first-year federal tax deduction for energy-efficient systems installed in commercial buildings. Taken in full in the year qualifying systems are placed in service, with no depreciation schedule. Rates were significantly expanded under the Inflation Reduction Act of 2022, and the One Big Beautiful Bill Act ended the deduction for projects that began construction after June 30, 2026. The deduction covers three qualifying systems.

Example qualifying equipment
    First-Year Deduction
    Taken in full in the year qualifying systems are placed in service. No depreciation schedule, no spreading the benefit over years.
    Look-Back Studies Available
    Design professionals may amend open prior-year returns under a 3-year look-back. Building owners can claim prior years via Form 3115 without amending.
    Stacks with Cost Segregation
    179D and Cost Segregation are complementary. 179D reduces building basis first; Cost Segregation then reclassifies remaining components into accelerated recovery categories.
    Deduction Limits
    Building Owners
    Limited to the cost of the qualifying energy systems (envelope, HVAC and hot water, interior lighting), not the full project cost.

    Design Professionals
    Limited to the owner's installed cost of the qualifying energy systems under IRS Notice 2008-40, not the design fee.
    2026 Deduction Rates

    How Much Is the 179D Deduction Worth?

    The 179D deduction ranges from $0.59 to $5.94 per square foot in 2026. The exact rate depends on two factors: the percentage of energy savings above the applicable ASHRAE 90.1 baseline (90.1-2007 for property placed in service before 2027, and 90.1-2019 for most property placed in service in 2027 or 2028, per IRS Announcement 2024-24), and whether the project complies with prevailing wage and apprenticeship (PWA) requirements. PWA-compliant projects qualify for a rate five times the non-PWA base.

    The 2026 maximum is $5.94 per square foot, achievable by projects meeting PWA requirements at 50% or more energy savings above the ASHRAE Standard 90.1 baseline.

    Rate Category Energy Savings Threshold Status Per Sq Ft
    Placed in Service Through 2022 (Partial)
    Per-system partial deduction. Thresholds varied by system: 10% envelope, 15% HVAC, 25% lighting.
    		 Varied by system Legacy Up to $0.63
    Placed in Service Through 2022 (Maximum)
    All three systems at or above 50% energy savings threshold. Whole-building full deduction.
    		 50%+ all systems Legacy Up to $1.88
    Placed in Service 2023+ (Non-PWA)
    Per-percentage-point scaling above 25% savings. No prevailing wage requirement.
    		 25% to 55%+ Current $0.59 to $1.19
    Placed in Service 2023+ (PWA Bonus)
    Prevailing wage and apprenticeship compliance required. Five times the non-PWA base rate.
    		 25% to 50%+ 2026 Max $2.97 to $5.94
    Through 2022 (Partial)
    Up to $0.63/sqft
    Legacy per-system partial deduction. Thresholds varied over the program's history.
    Through 2022 (Maximum)
    Up to $1.88/sqft
    Legacy maximum. All three systems at full threshold. 50%+ energy savings.
    2023+ (Non-PWA)
    $0.59 to $1.19/sqft
    Per-percentage-point scaling above 25% savings. No prevailing wage requirement.
    2023+ (PWA Bonus)
    $2.97 to $5.94/sqft
    Prevailing wage and apprenticeship required. Five times the non-PWA base rate.
    Does §179D apply to multifamily buildings? Yes. Residential buildings four stories or taller qualify under §179D. Multifamily apartment buildings, condominiums, and similar residential structures meeting the four-story requirement are eligible at the same rates above. Buildings under four stories are not eligible for §179D but may qualify for other incentives.
    Eligibility Check
    !
    The IRC §179D Construction Start Deadline Passed on June 30, 2026 Under the One Big Beautiful Bill Act (OBBBA), §179D does not apply to property whose construction began after June 30, 2026. Projects that began construction on or before that date still qualify when they are placed in service, and completed buildings remain eligible for look-back claims. For in-progress projects, the construction start date is now the basis for eligibility.

    Did Your Project Begin Construction
    by June 30, 2026?

    If it did, it remains eligible when placed in service, even if construction runs into 2027 or later. Practitioners establish the start date with the beginning-of-construction framework the IRS has long used for energy incentives: the Physical Work Test or the 5% Safe Harbor, followed by continuous progress toward completion. Documenting which test your project met is now the most important step in the claim.

    1
    Method 1
    Physical Work Test
    Met if "physical work of a significant nature" on the qualifying systems began on or before June 30, 2026: interior lighting, HVAC and hot water, or the building envelope. The test looks at the nature of the work, not its cost.
    Qualifying On-Site Work
    • Setting HVAC equipment, or running ductwork and hydronic piping
    • Installing envelope assemblies: insulation (including under-slab and slab-edge), roofing, glazing, or curtain wall
    • Installing interior lighting fixtures and controls
    Qualifying Off-Site Work
    • Air handlers, rooftop units, or chillers built to project specifications
    • Curtain wall or wall panels fabricated for the project
    • Both under a binding written contract signed before fabrication began
    Does NOT Count Planning, design, financing, permits, surveys, engineering studies, and site clearing. Structural work alone, such as foundations, slabs, and framing, since it is not part of a qualifying system. Equipment taken from a vendor's standard inventory.
    Keep the Work Moving
    After the start, work must continue toward completion. The IRS has not set a fixed continuity safe harbor for 179D, so delays are judged on the facts, which makes a dated record of progress important.
    2
    Method 2
    5% Safe Harbor
    Met if the taxpayer had paid or incurred at least 5% of total project cost on or before June 30, 2026, then made continuous efforts toward completion. We confirm the cost basis in the study.
    How the 5% Is Calculated
    Measured against total project cost: all costs included in the building's depreciable basis. Land costs are excluded.
    Eligible Costs Include
    • Materials, equipment and labor paid or incurred under binding contracts
    • Lighting, envelope and HVAC equipment and materials
    • Components fabricated off-site (e.g., custom HVAC units)
    • Design and engineering fees, reviewed case by case since preliminary work may not count
    What to Gather Now Binding contracts, paid invoices, construction logs, and dated site photos from on or before June 30, 2026. The 5% test also needs a reliable estimate of total project cost. Collect these while project teams and records are still easy to reach.
    Book a Discovery Call

    We identify qualifying projects and confirm eligibility before you commit to a study.

    Who Can Claim

    Who Can Claim the 179D Deduction?

    Building owners and design professionals both qualify for the §179D deduction, but through completely different mechanisms. Understanding which path applies determines the entire study structure.
    Architects · MEP Engineers · Design-Build

    Yes. Architects and Engineers Can Claim §179D

    When a qualifying building is owned by a government or tax-exempt entity, the deduction cannot be claimed by the owner. Instead, it is allocated to the design professional who designed the qualifying energy systems: architects, MEP engineers, and design-build contractors.

    • Public schools, universities, and community colleges
    • Federal, state, and municipal buildings
    • Nonprofit hospitals and tax-exempt healthcare facilities
    • Libraries, courthouses, public safety buildings
    • Tribal governments and tribal enterprises
    Look-Back: Designers claim by amending the return for the year the building was placed in service, while that year is still open (generally three years).
    Cap: Limited to the owner's installed cost of the qualifying energy systems, not the design fee.
    Owners · Developers · Investors

    Building Owners Claim Directly

    For-profit building owners claim the §179D deduction directly on their tax return. Pass-through entities (LLCs, S-Corps, and partnerships) flow the benefit to individual owners. No allocation required.

    • Commercial property owners: office, retail, industrial
    • Multifamily residential buildings (4 stories or taller)
    • Hotels, mixed-use, and owner-occupied commercial buildings
    • Pass-through entities (LLC, S-Corp, partnership)
    • REITs (with 5-year spread for earnings and profits purposes)
    Prior Years: Owners can claim prior years through a Form 3115 accounting method change. No amended return required.
    Cap: Limited to the cost of the qualifying energy systems, not the full project cost.

    Investors & REITs

    Investors in pass-through entities (LLCs, S-Corps, partnerships) receive their share of the §179D deduction as a pass-through item. REITs claim the deduction directly but must spread it over 5 years for earnings and profits purposes under §857.

    Design-Build Contractors

    When a building is owned by a government or tax-exempt entity, the deduction can be allocated to the contractor that designed the qualifying mechanical, lighting, or envelope systems. Not just the general contractor. The design responsibility is determinative.

    See how 179D applies across property types and ownership structures at our Industries page.

    Example Projects

    179D Deduction Examples by Building Type

    These examples show the 179D deduction applied at the 2026 PWA maximum of $5.94 per square foot. Actual deduction depends on building type, systems installed, energy savings achieved, and PWA compliance. aecre's feasibility study projects your specific range before any commitment.
    Project Type → Recipient Claim Type Sq Ft Deduction at $5.94/sqft
    Public School
    Engineering Firm (Allocated)
    		 Allocated 150,000 $891,000
    Nonprofit Hospital
    MEP Firm (Allocated)
    		 Allocated 200,000 $1,188,000
    Private Office Building
    Building Owner (Direct)
    		 Owner 120,000 $712,800
    City Library
    Architecture Firm (Allocated)
    		 Allocated 65,000 $386,100
    State University
    Design-Build Firm (Allocated)
    		 Allocated 300,000 $1,782,000
    Public School
    Engineering Firm
    $891,000
    Allocated150,000 sq ft
    Nonprofit Hospital
    MEP Firm
    $1,188,000
    Allocated200,000 sq ft
    Private Office Building
    Building Owner
    $712,800
    Owner120,000 sq ft
    City Library
    Architecture Firm
    $386,100
    Allocated65,000 sq ft
    State University
    Design-Build Firm
    $1,782,000
    Allocated300,000 sq ft
    Step 1

    Project Parameters

    Both dates refer to the qualifying lighting, HVAC, or envelope work. For a renovation, use the renovation's dates, not the building's.
    Systems in Scope
    Select at least one system to continue.
    Step 2

    Estimated Deduction

    Get a report for every building

    The 179D Deduction Calculator values each building you own or designed under its own year's rules, using the savings our completed studies achieved.

    Open the 179D Deduction Calculator
    Deduction Rate by Energy Savings
    Energy Savings vs. ASHRAE Baseline
    50%

    Methodology. This estimate is based on published IRS deduction rate schedules for the selected placed-in-service year. Actual deduction value is determined by energy modeling results, site inspection, and certification by a licensed Professional Engineer. This does not constitute tax advice.

    * At the 2026 PWA maximum rate of $5.94/sq ft. Actual results depend on qualifying systems installed, energy savings percentage against the applicable ASHRAE 90.1 baseline, and prevailing wage compliance. aecre's feasibility study projects your specific range before you commit.
    Maximize Your First-Year Benefit

    179D + Cost Segregation:
    A Powerful Combination

    §179D reduces the building's depreciable basis as a first-year deduction on 39-year Section 1250 property. Cost Segregation then reclassifies remaining building components into 5, 7, and 15-year recovery categories. With 100% bonus depreciation permanently restored under OBBBA for property acquired after January 19, 2025, those reclassified components can qualify for a full first-year write-off. Applied together on a new build or renovation, the combined first-year tax impact can be substantially larger than either incentive alone.

    Note: aecre coordinates Cost Segregation studies with qualified providers. We do not perform them in-house.

    Learn About Cost Seg →
    Our Process

    How Does a 179D Study Work?

    Eight steps from initial portfolio review to CPA integration. Every study is certified by a Professional Engineer licensed in the state where the building is located. We work directly with your CPA so nothing falls through the cracks.
    01

    Feasibility Study

    Project 179D deduction value for target buildings based on historical study data and your specific building parameters. No commitment required.

    05

    Field Inspection

    IRS-required, third-party site visit conducted by aecre's in-house Professional Engineers. We fly to your building. No subcontracting the engineering work.

    In-House PE · Licensed in Building's State
    02

    Portfolio Review

    Identify all qualifying buildings in your portfolio and estimate total deduction potential across the full lookback window.

    06

    Certification

    Certify the 179D study methodology and results by a Professional Engineer licensed in the building's state. The IRS requirement no third-party firm can shortcut.

    PE-Stamped Certification · State-Licensed
    03

    Documentation

    Collect and review project plans, schedules, costs, and contracts to confirm the study plan and establish the substantiation record.

    07

    Study Results

    Deliver the Building Report, PE Certification, Tax Form 7205, and all study materials required for IRS substantiation and CPA reporting.

    04

    Energy Modeling

    Quantify the building's energy savings against the applicable ASHRAE 90.1 reference standard: 90.1-2007 for property placed in service before 2027, and 90.1-2019 for most property placed in service in 2027 or 2028.

    08

    CPA Integration

    Work directly with your CPA to report deductions accurately and defensibly. We provide everything they need: the study, the Form 7205, and the PE certification. They can file with confidence.

    Study Deliverables

    What's in Your 179D Study Report

    Cover and Executive Summary

    Deduction summary, energy modeling tables and graphs, and qualifying building details.

    PE Certification

    Signed and sealed by a Professional Engineer licensed in your building's state.

    Energy Efficient Features

    Qualifying building features documented per system: envelope, lighting, and HVAC.

    IRS Form 7205

    Prepared and ready for your CPA with all required fields populated.

    Substantiation File

    Full substantiation file retained for audit defense. Project documents, cost records, and contracts organized and preserved.

    What to Expect

    From Kickoff to Delivered Study

    Typical Timeline

    4 to 8 weeks for a single building. 8 to 12 weeks for portfolio engagements.

    Site visits scheduled within 2 weeks of engagement.

    What We Need From You

    Construction documents and as-built drawings. Cost records (architect and contractor invoices). HVAC and lighting equipment specs where available. CPA contact for filing coordination.

    What You Don't Need

    Engineering expertise. Energy modeling knowledge. Time for the site visit. We coordinate with the property manager, not you.

    FAQ

    Frequently Asked Questions About the 179D Deduction

    Straight answers to the questions we hear most from building owners, architects, and developers. Additional technical detail available on request.

    IRC §179D provides a first-year federal tax deduction for energy-efficient systems installed in commercial buildings. Taken in full in the year qualifying systems are placed in service, with no depreciation schedule. It covers three qualifying systems: interior lighting, HVAC and hot water, and building envelope. Rates were significantly expanded under the Inflation Reduction Act of 2022. Under the One Big Beautiful Bill Act, projects that began construction after June 30, 2026 do not qualify, while projects that began on or before that date remain eligible when placed in service. For building owners, the deduction is claimed directly on their return. For buildings owned by government or tax-exempt entities, the deduction is allocated to the design professional who designed the qualifying systems.
    In 2026, the §179D rate ranges from $0.59 to $5.94 per square foot, depending on energy savings achieved and PWA compliance. Non-PWA projects qualify for $0.59 per square foot at 25% energy savings, rising $0.02 per percentage point to $1.19 at 55% savings. PWA-compliant projects qualify for $2.97 per square foot at 25% savings, rising $0.12 per percentage point to the $5.94 maximum at 50% savings. Savings are measured against the applicable ASHRAE 90.1 reference standard.
    Yes. Architects, MEP engineers, design-build contractors, and other design professionals can claim §179D when they design qualifying energy systems for buildings owned by government or tax-exempt entities: public schools, universities, hospitals, libraries, and municipal buildings. The building owner allocates the deduction to the designer. The designer's deduction is limited by the owner's installed cost of the qualifying energy systems, not by the design fee. Designers claim prior years by amending the return for the year the building was placed in service, while that year remains open, generally three years.
    June 30, 2026, and it has passed. Under the One Big Beautiful Bill Act, §179D does not apply to property whose construction began after June 30, 2026. Projects that began construction on or before that date still qualify when they are placed in service, including in 2027 or later. The start date is established with the Physical Work Test (physical work of a significant nature on qualifying systems by the deadline) or the 5% Safe Harbor (at least 5% of total project cost paid or incurred by June 30, 2026), followed by continuous progress toward completion. Completed buildings are not affected and remain eligible for look-back claims.
    Yes, for buildings four stories or taller. Multifamily residential buildings at four stories or more qualify under §179D at the same rates as commercial property. Apartment buildings, condominiums, and similar residential structures meeting the height requirement are eligible. Residential buildings under four stories are not eligible for §179D but may qualify for other federal or state incentives.
    The PWA (prevailing wage and apprenticeship) bonus rate is five times the non-PWA base rate. Non-PWA projects qualify for $0.59 to $1.19 per square foot based on energy savings percentage. Projects complying with prevailing wage requirements and employing qualified apprentices for a specified percentage of labor hours qualify for $2.97 to $5.94 per square foot. PWA compliance must be documented and maintained throughout construction and is verified as part of the 179D study process.
    Yes. Building owners can claim prior-year §179D deductions through a Form 3115 accounting method change. No amended return required. Design professionals who received allocated deductions can amend open prior-year returns under a 3-year look-back. aecre's portfolio review identifies qualifying prior-year projects before you commit to a study. Many building owners discover significant unclaimed deductions in buildings placed in service 2 to 5 years prior.
    Yes, for new projects. The One Big Beautiful Bill Act terminated the §179D deduction for property whose construction began after June 30, 2026. Projects that began construction on or before that date remain eligible when they are placed in service, even if they finish in 2027 or later, and existing buildings already placed in service remain eligible for prior-year look-back studies. For those projects, documenting the construction start date is now the most important step in the claim.

    Book Your
    Portfolio Review

    We identify qualifying buildings, project your deduction range, and give you a clear picture of what §179D is worth for your portfolio, before you commit to anything. We work directly with your CPA so the process is seamless.

    Book a Discovery Call

    No obligation. No commitment.

    Or reach us directly.

    Taylor Beamer, PE
    Partner, Operations and Engineering
    [email protected] 832-217-4469
    Brandon Carroll
    Partner, Growth and Strategy
    [email protected] 857-997-4141
    We respond within 1 business day