Three Paths to IRC 2024 Energy Code Compliance

Quick Answer

IRC 2024 Section N1101.13 offers three compliance paths for new one- and two-family dwellings: (1) the Prescriptive path, which requires meeting every minimum value in Table N1102.1.3 for your climate zone; (2) the Performance path using REScheck software to show equivalent whole-building energy performance; and (3) the Energy Rating Index (ERI) path, which requires achieving a specific ERI score that tightened by approximately 5 points from IRC 2021 in most climate zones. The ERI path allows trading off components, and a HERS rating is required to document the score.

What IRC 2024 Actually Requires

IRC 2024 N1101.13 establishes three distinct pathways to energy code compliance. Each path leads to the same destination — a code-compliant new home — but with different tools, flexibility, and documentation requirements.

Path 1: Prescriptive Compliance. The simplest path. The building must meet every minimum or maximum value listed in Table N1102.1.3 for its climate zone. This includes: attic insulation R-value, wall assembly R-value, floor and basement insulation R-values, window and door U-factor and SHGC, and air leakage (blower door test). There is no flexibility between components; a low-performing window cannot be offset by extra attic insulation. All components must independently meet their table values. Documentation is the energy certificate posted near the electrical panel listing all installed values.

Path 2: Performance Compliance (REScheck). The builder models the home using the DOE’s free REScheck software. The software calculates the annual energy budget of the proposed design and compares it to a reference design that meets all prescriptive requirements. If the proposed design’s calculated energy use is equal to or less than the reference design’s, it complies. This allows tradeoffs: a large window area facing south can be offset by extra wall insulation or a higher-efficiency HVAC system. The REScheck report must be submitted with the permit application and retained by the building official. The software is free from the DOE and widely used by builders and designers.

Path 3: Energy Rating Index (ERI) Compliance. The building must achieve an ERI score at or below the maximum value for its climate zone. IRC 2024 ERI targets tightened by approximately 5 points from IRC 2021 in most climate zones: Zone 1 from 65 to 62; Zone 2 from 63 to 59; Zone 3 from 60 to 55; Zone 4 from 55 to 51; Zone 5 from 52 to 47; Zone 6 from 48 to 44; Zone 7 from 46 to 42; Zone 8 from 44 to 40. The ERI is equivalent to the HERS (Home Energy Rating System) index, where a score of 100 represents the energy use of a reference home meeting the 2006 IECC. A RESNET-certified HERS rater must calculate and certify the ERI score. The ERI path is the most flexible because component tradeoffs are unlimited, but it requires a third-party rating at additional cost.

Why This Rule Exists

A single prescriptive table cannot accommodate the diversity of residential construction: varying floor plans, window orientations, roof slopes, climate sub-zones, and the full range of available insulation, glazing, and mechanical system products. Multiple compliance paths allow builders to optimize their designs within the overall energy budget rather than being locked into one-size-fits-all component minimums. The ERI path in particular enables innovative designs where a highly efficient HVAC system or PV-ready orientation can compensate for a complex glazing scheme that would fail the prescriptive window table. Offering multiple paths also encourages market innovation: manufacturers of high-performance components can demonstrate the value of their products through compliance paths that reward total performance rather than minimum compliance.

What the Inspector Checks at Rough and Final

The inspector’s role differs by compliance path. For prescriptive path projects, the inspector reviews the energy certificate at final against the Table N1102.1.3 values for the climate zone. They check blower door and duct leakage test reports as described in those respective code sections. For performance path projects (REScheck), the inspector verifies that the REScheck report was submitted with the permit application and that the installed components match what was modeled. If a project submitted prescriptive documentation but then field-substituted windows with a higher U-factor, the inspector will require either a new REScheck showing compliance with the substituted components or replacement with compliant windows. For ERI path projects, the inspector verifies that a HERS rating report is on file and that the ERI score meets the climate zone target. The HERS rater’s final rating report is the primary compliance document; the inspector reviews it and confirms the required tests (blower door, duct leakage) were performed as part of the rating.

What Contractors Need to Know

Choose your compliance path before finalizing the design, not after. The prescriptive path is fastest for straightforward projects in climate zones 1 through 4 where meeting the table values is not a design challenge. For Zone 5 and above or for projects with large glazing areas, contemporary open-plan designs, or complex roof lines, REScheck or ERI path provides flexibility that the prescriptive path does not. REScheck is free, fast, and widely accepted; most permit offices accept a REScheck report in lieu of a prescriptive checklist. The ERI path adds cost (HERS rating typically $400 to $800) but is the most powerful tool for custom home builders who want to document a high-performance design or trade off components aggressively. One caution on the ERI path: the ERI score must be certified before occupancy, meaning the rater must complete all required tests and modeling before the final CO is issued. Do not use the ERI path if you cannot coordinate the rating timeline with the construction schedule.

What Homeowners Get Wrong

A common question: “My builder said they use REScheck, so does that mean my house will be more energy efficient than a prescriptive house?” Not necessarily. REScheck demonstrates equivalent energy performance, not superior performance. A builder can use REScheck to justify installing cheaper windows by adding more attic insulation, and the house’s calculated energy budget may be the same as a prescriptive-path house, not better. Another misunderstanding: “The HERS score is the same as the ERI score, right?” The HERS index and the ERI score are based on the same methodology and produce identical numbers for new construction in most cases. The distinction is that “ERI” is the code term used in the IRC, while “HERS” is the industry and market term used by RESNET. Homeowners also sometimes think that a low HERS score from the ERI path guarantees lower utility bills; HERS predicts energy use under standard assumptions, but actual bills depend on occupant behavior, local utility rates, and weather conditions.

State and Local Amendments

Several states mandate a specific compliance path. California requires Title 24 compliance software (EnergyPro or equivalent) rather than REScheck; there is no prescriptive table approach for standard new construction in California. Washington State accepts REScheck and performance compliance but has its own WSEC prescriptive tables. New York allows all three IRC paths but the stretch energy code requires the ERI path with a HERS rating in many municipalities. Massachusetts stretch code requires the ERI path for new construction in most jurisdictions, with a HERS index target of 55 or below. Colorado has adopted the 2021 IECC with the three compliance paths, and many Front Range municipalities require the ERI path with HERS ratings. Check with the local building department before selecting a compliance path, as the jurisdiction may have eliminated one or more options.

When to Hire a Professional

For the prescriptive path, a competent contractor or designer can fill out the energy certificate without a specialist if they know the climate zone requirements. For REScheck, the software is free and relatively user-friendly; many designers and builders run their own REScheck analyses. For the ERI path, a RESNET-certified HERS rater must be engaged and should be brought in during the design phase, not after construction is complete. A rater who reviews plans before construction can identify whether the design will achieve the target ERI score and flag tradeoffs or component upgrades needed before any materials are ordered. Retrofitting a design to meet ERI targets after construction is far more expensive than getting it right at the design stage.

Common Violations Found at Inspection

• Prescriptive path project has an energy certificate listing window U-factors that do not match the NFRC labels on installed windows; the substituted windows require either a code correction or a REScheck demonstrating compliance with the substituted values.
• REScheck was submitted with the permit application but models a different window area than was actually constructed; the inspector requires a revised REScheck reflecting as-built conditions.
• ERI path project has no HERS rating on file at final inspection; the builder expected to submit it later, but the code requires the rating before the certificate of occupancy is issued.
• Prescriptive path project in Zone 5 lists R-49 attic insulation, which met the 2021 table but fails the 2024 requirement of R-60; the contractor did not update specifications when the jurisdiction adopted IRC 2024.
• REScheck analysis models a high-efficiency HVAC system to offset a large glazing area, but the installed HVAC equipment is a lower-efficiency unit; the inspector requires revised compliance documentation.
• Energy certificate near the panel is missing entirely; all three compliance paths require an energy certificate, and its absence is a consistent cause of failed final inspections.
• Blower door test result is not included on the energy certificate regardless of compliance path; all three paths require testing documentation under N1102.4.1.2.
• ERI path report uses a software tool not recognized by the building official; only RESNET-accredited software producing a certified HERS rating is acceptable for the ERI path in most jurisdictions.