Comparative ASHRAE Standard 90.1 Reference-Building Energy Deduction Modeling and Cryptographic Workpaper Attestation under Internal Revenue Code Section 179D (26 U.S.C. § 179D)

Internal Revenue Code Section 179D (26 U.S.C. § 179D), as restructured by the Inflation Reduction Act of 2022 (Pub. L. 117-169), amended as to construction-start sunset by Pub. L. 119-21 § 70507, and indexed for inflation under IRS Revenue Procedure 2024-40 (Tax Year 2025) and Revenue Procedure 2025-32 Section 4.25 (Tax Year 2026), provides an accelerated per-square-foot tax deduction for energy-efficient commercial building property (EECBP) and energy-efficient building retrofit property (EEBRP) achieving at least a 25% reduction in total annual energy and power costs across interior lighting, HVAC and service hot water, and building envelope systems relative to an ASHRAE Standard 90.1 reference building (for property whose construction begins on or before June 30, 2026). For 2026 placed-in-service dates, statutory rates span USD 0.59 to USD 1.19 per square foot (base tier) and USD 2.97 to USD 5.94 per square foot when Prevailing Wage and Apprenticeship (PWA) requirements under IRC § 179D(b)(3)-(5) are satisfied (up from USD 0.58–1.16 and USD 2.90–5.81 in 2025, and the USD 0.50–1.00 and USD 2.50–5.00 statutory baseline), claimed via IRS Form 7205 and allocable to primary designers of government and tax-exempt entity buildings under § 179D(d)(4). IRS Large Business and International (LB&I) examinations routinely disallow § 179D claims due to four technical defects: improper ASHRAE 90.1 edition selection (90.1-2007 vs. 90.1-2019 under IRS Announcement 2024-24), floating-point and Worksheet Line 2a rounding errors across sliding-scale increments, violation of the rolling three-tax-year (or four-tax-year designer) aggregate per-square-foot cap (§ 179D(b)(2) and Form 7205 Part I), and unsealed decoupling between DOE-qualified simulation outputs, physical site inspection records, and CPA tax schedules. This technical note formalizes a deterministic 0-ULP fixed-point § 179D rate-interpolation, basis-cap, and RFC 8785 cryptographic workpaper attestation protocol. Reference Implementation & Archival Availability: A deterministic zero-egress WebAssembly (WASM) reference verification engine implementing the formal invariants specified in this monograph is maintained by TITAN Capital Forensics LLC (Albuquerque, New Mexico, USA; ORCID: 0009-0005-3920-2333) at 179dshield.com. No source code or executable software is distributed within this technical monograph.