The 179D tax deduction and 45L credit ended for new projects after June 30, 2026. Compare 10 firms that help claim eligible projects and look-backs.
Two energy incentives that real estate owners, designers and homebuilders relied on for years are winding down. The One Big Beautiful Bill Act, signed July 4, 2025, ended the 179D tax deduction, formally the energy efficient commercial buildings deduction, for buildings whose construction begins after June 30, 2026. It also ended the 45L tax credit for new energy efficient homes acquired, meaning sold or leased, after June 30, 2026. Before the 2025 law, 179D was a permanent provision and 45L ran through 2032.
That does not mean the work is over. A 179D project that began construction on or before June 30, 2026 can still qualify even if it is placed in service later, and owners of recently completed buildings who never claimed 179D may be able to claim it through a Form 3115 accounting method change or an amended return within the statute of limitations. For 45L, homes and units acquired on or before June 30, 2026 can still be claimed if they meet the certification rules. Any extension would need new legislation, so plan around the current deadlines.
We chose these firms because they publish real 179D or 45L capabilities: energy modeling, third-party certification, designer allocation letters for government and nonprofit buildings, and look-back studies. Several also offer cost segregation, which pairs naturally with 179D on the same building. Confirm eligibility for any specific project with your CPA.
179D And 45L Firms At A Glance
Company
Headquarters
Best For
Standout
KBKG
Pasadena, CA
Designers, owners and multifamily developers
Engineers plus tax team, 45L third-party verifier
Walker Blue
Boca Raton, FL
Builders and energy-heavy portfolios
In-house energy engineering and modeling
Engineered Tax Services
West Palm Beach, FL
Owners wanting 179D with cost segregation
Licensed engineering firm, 25+ years
Tri-Merit
Schaumburg, IL
CPA firms and their clients
Engineer and CPA-led, covers both 179D and 45L
Leyton
Boston, MA (US)
Owners wanting energy modeling in-house
Dedicated 179D, 45L and energy modeling services
Capstan Tax Strategies
Dresher, PA
Architects, engineers and commercial owners
Engineers, tax attorneys and analysts
CSSI
Baton Rouge, LA
High-volume commercial portfolios
46,000+ studies since 2003
Source Advisors
Arlington, TX
Companies bundling several specialty studies
40+ years in specialty tax
McGuire Sponsel
National footprint
CPA firms and mid-market owners
179D within a fixed asset practice
Onshore
New York, NY
Smaller owners and design firms
Fast turnaround, audit support included
Best 179D And 45L Tax Incentive Firms In 2027
1. KBKG — Engineering And Tax Team For 179D Plus 45L Certification
KBKG uses a multidisciplinary team of engineers and tax specialists for 179D, building each claim on the detailed engineering analysis the IRS requires and comparing the building to ASHRAE standards. It handles designer allocations for government and tax-exempt buildings, such as schools, universities, churches and public buildings, and helps clients claim deductions missed in prior years. It tells design firms to treat June 30, 2026 as a project screening and documentation deadline.
For 45L, KBKG acts as a qualified third-party verifier and says it has advised affordable housing and other developers since 1999. Its 45L page targets developments of 20 or more units built or renovated in the past four years.
KBKG also offers cost segregation and R&D credits from offices in Pasadena, New York, Atlanta, Chicago, Dallas and Houston.
Best for: Architects, engineers and multifamily developers who need both 179D and 45L handled by one specialist.
2. Walker Blue — Energy Engineering Firm For 179D, 45L And ITC Work
Walker Blue is headquartered in Boca Raton, Florida (the former walkerreid.com domain now redirects to its site). It lists 179D deductions, 45L credits for single-family and multifamily homes, investment tax credit work including cost segregation for ITC projects, domestic content analysis, and prevailing wage and apprenticeship compliance.
Its in-house energy engineering services include energy audits, building energy modeling, measurement and verification and retrocommissioning. That is useful for 45L and 179D, where certification depends on modeling and testing, and for owners moving their attention to other credits after June 30, 2026.
It also runs a residential energy programs group, which fits homebuilders closing out their final 45L-eligible homes.
Best for: Homebuilders and owners who want energy engineering and incentives under one roof.
Engineered Tax Services is headquartered in West Palm Beach, Florida, with offices in Dallas, Charlotte, Las Vegas, Los Angeles, New York, Phoenix and Raleigh. It describes itself as an independent, licensed engineering firm with more than 25 years of experience, and lists 179D, 45L, cost segregation and R&D credits among its services.
ETS has published plainly that 179D is terminated for property whose construction begins after June 30, 2026, and that the test is the construction start date, not the placed-in-service date. It also explains the look-back route: owners who never claimed 179D on recently completed buildings may use a Form 3115 accounting method change, or an amended return within the three-year statute of limitations.
Pairing 179D with a cost segregation study on the same building can reduce duplicate site work.
Best for: Commercial owners who want a final 179D claim coordinated with cost segregation.
4. Tri-Merit — Engineer And CPA-Led Specialty Tax Partner For Both Incentives
Tri-Merit is based in Schaumburg, Illinois, with regional offices in Ann Arbor, Michigan, and Tysons Corner, Virginia. It describes its team as engineer and CPA-led and lists both Section 179D and 45L among its services, alongside cost segregation, R&D credits, renewable energy credits and tax audit defense.
Tri-Merit works mainly through CPA firms, plugging into the accountant’s workflow so the CPA keeps the client relationship. That suits owners and builders whose outside CPA wants to close out remaining 179D and 45L claims without hiring a specialist team of their own.
It lists AICPA and CPAConnect affiliations.
Best for: CPA firms and their clients who want 179D and 45L claims delivered behind the accountant.
5. Leyton — Dedicated 179D, 45L And Energy Modeling Services
Leyton lists Section 179D, Section 45L and energy modeling as separate offerings in its real estate tax optimization practice. Its U.S. team of more than 70 specialists includes accountants, scientists, engineers and doctors, with offices in Boston, New York, Houston, Tempe and the San Francisco Bay Area.
Leyton has published guidance on the 2026 sunset of 179D and on 2026 inflation-adjusted 179D values, which helps owners understand what their final eligible projects are worth. Globally, it operates in 20 countries and reports more than 50,000 clients.
It also offers cost segregation, so real estate clients can bundle work on the same property.
Best for: Owners and developers who want energy modeling and incentive filing handled by one team.
Capstan Tax Strategies is based in Dresher, Pennsylvania, and describes a multidisciplinary team of engineers, tax attorneys and analysts. Clients work with the same engineers and specialty tax staff from project to project.
Its energy incentive work covers the 179D deduction, the investment and clean electricity investment credits and the EV charging station credit. It also runs cost segregation studies for hotels, retail, restaurants and self-storage, and R&D credit studies for architecture and engineering firms, which overlap with the designers who claim 179D allocations.
Capstan also runs Capstan University training and predominant use studies. It does not list 45L, so homebuilders should look elsewhere for that credit.
Best for: Architecture and engineering firms and commercial owners closing out 179D claims.
7. CSSI — High-Volume Specialty Tax Firm Since 2003
CSSI was founded in 2003 and is headquartered in Baton Rouge, Louisiana. It reports more than 46,000 studies completed and lists cost segregation, Section 179D and R&D tax credits as its services, with a national network of local representatives matched to each property.
CSSI offers a directory of experts and assigns a local representative based on where the property sits, which helps owners with buildings spread across several states. Combining 179D and cost segregation in one review avoids paying for two separate site visits.
That volume suits owners and CPA firms with many buildings to review before 179D look-back windows close. CSSI does not list 45L.
Best for: Commercial portfolio owners who want 179D reviewed alongside cost segregation on many properties.
8. Source Advisors — Specialty Tax Firm With 179D In A Broad Incentives Practice
Source Advisors is headquartered in Arlington, Texas, and says it has operated for more than 40 years. Its energy tax incentive work includes 179D deductions, and it also offers cost segregation, R&D credits, Section 174 analysis, sales and use tax, LIFO and property tax.
Its R&D team includes CPAs, attorneys, engineers and technology specialists, and the firm hires remote consultants nationwide for on-site property work. Ask it to screen older buildings for missed 179D claims while the statute of limitations is still open.
For manufacturers and companies with owner-occupied facilities, that breadth means one provider can review a building for 179D, cost segregation and other benefits together. It does not list 45L.
Best for: Mid-size companies that own their facilities and want several specialty studies coordinated.
9. McGuire Sponsel — 179D Inside A Fixed Asset And Incentives Practice
McGuire Sponsel offers 179D within its fixed asset practice, alongside cost segregation and qualified production property guidance for CPA firms. It also provides R&D credits, IC-DISC, transfer pricing, site selection and incentive compliance, and property tax services.
The firm works closely with regional CPA firms and runs an alliance network for needs outside its own services, which suits accountants who want a specialty partner to finish remaining 179D claims for clients. Its named team includes enrolled agents and CPAs, and it serves about ten industries. It also runs planning webinars and a podcast that track tax law changes. It does not list 45L.
Best for: Regional CPA firms and mid-market owners who want 179D handled by a fixed asset specialist.
10. Onshore — Fast-Turnaround 179D Studies With Audit Support
Onshore is a New York-based firm best known for R&D credits that also offers 179D energy-efficient building deductions and cost segregation. It reports more than 500 companies served, an average turnaround of two to three weeks, and audit support in every engagement.
A credentialed tax professional reviews every number before filing. Onshore is SOC 2 Type II compliant and keeps client data in the United States. It also prepares amended returns, which is relevant for owners trying to recover a missed 179D deduction from an earlier year. It offers a free assessment and charges a share of what it recovers. It does not list 45L.
Best for: Smaller owners and architecture and engineering firms that want a quick 179D review.
How To Choose A 179D Or 45L Firm
Does Your Project Still Qualify?
The 179D deadline turns on when construction began. Projects that began on or before June 30, 2026 can still qualify, and Treasury is expected to apply a facts-and-circumstances test, with physical work of a significant nature or a 5% safe harbor as possible methods. For 45L, the key date is when the home was sold or leased. Ask the firm to confirm eligibility in writing before you pay for modeling.
Can They Do Look-Backs And Amended Claims?
Much of the remaining value is in buildings already placed in service. Ask whether the firm prepares Form 3115 support or amended return packages, and which tax years are still open.
Who Certifies The Work?
179D needs a qualified energy study and third-party certification, and 45L needs certification and testing by a qualified verifier. Ask who performs the modeling and testing, and whether they are in-house or subcontracted.
Can They Handle Designer Allocations?
Architects, engineers and design-build contractors can claim 179D on government and certain nonprofit buildings with a signed allocation letter from the owner. Choose a firm that has secured these letters before.
Is The 179D Tax Deduction Still Available In 2027?
Only for property whose construction began on or before June 30, 2026, including projects placed in service later, and through look-back claims on qualifying buildings already in service. It is not available for projects that begin construction after that date. A bill to preserve 179D was introduced in April 2026, but it is not law.
Can I Still Claim 45L?
Yes, for qualifying homes and units acquired on or before June 30, 2026 that meet the energy and certification requirements. Homes sold or leased after that date do not qualify, even if construction finished earlier.
How Much Is 179D Worth For 2026 Projects?
For tax years beginning in 2026, published figures range from about $0.59 to $1.19 per square foot at the base rate, and about $2.97 to $5.94 per square foot when prevailing wage and apprenticeship requirements are met. Your firm will calculate the exact amount.
Conclusion
The 179D tax deduction and the 45L credit are closing, not continuing. The value that remains sits in projects that began construction or homes that were acquired by June 30, 2026, and in look-back and amended claims on buildings already in service. The firms above can model, certify and document those final claims, and several can pair them with cost segregation. Act while the statute of limitations is still open, and confirm every claim with your CPA. For broader planning, see our list of tax strategy firms for real estate investors.
This article is general information, not tax or legal advice.
