3.1 R401.2 Application: Prescriptive, Performance, ERI & Tropical Options
Key Takeaways
- Residential buildings shall comply with R401.2.5 additional energy efficiency and either R401.2.1, R401.2.2, R401.2.3, or R401.2.4.
- Prescriptive R401.2.1 requires Sections R401 through R404; performance R401.2.2 requires R405; ERI R401.2.3 requires R406; tropical R401.2.4 requires R407.
- R401.2.5 sits on every primary path: one R408.2 package (prescriptive), an R408.2 package omitted from the R405 proposed design or proposed annual energy cost at or below 95 percent of the standard reference design (performance), or an ERI at least 5 percent less than Table R406.5 (ERI).
- The compliance path and the additional-efficiency option selected shall be identified on the R401.3 certificate and should be declared on the construction documents before envelope numbers are reviewed.
- The four primary options are alternatives, not a buffet; a UA worksheet, an R405 report, and an ERI score are not interchangeable evidence.
3.1 R401.2 Application: Prescriptive, Performance, ERI & Tropical Options
Quick Answer: Under the 2021 IECC, residential buildings shall comply with Section R401.2.5 and either Section R401.2.1 (prescriptive, R401 through R404), R401.2.2 (total building performance, R405), R401.2.3 (Energy Rating Index, R406), or R401.2.4 (tropical climate region, R407). The additional-efficiency option selected is identified on the R401.3 certificate.
Section R401.2 is the application rule that tells a plans examiner which residential energy path is on the table. Independent OpenExamPrep material for ICC Exam 79 treats it as a documentation decision, not a marketing slogan. Until the drawings name a path, Table R402.1.3 R-values, an R405 printout, and an ERI score are competing attachments rather than a compliance showing.
The two-part 2021 rule
The charging sentence is short and easy to misread. Residential buildings shall comply with Section R401.2.5 and either Sections R401.2.1, R401.2.2, R401.2.3, or R401.2.4.
Read the and first. Additional energy efficiency in R401.2.5 applies to every approach. A complete prescriptive envelope that never installs an R408.2 package does not comply. An R405 run that neither installs an R408.2 package without including those measures in the proposed design nor shows proposed annual energy cost less than or equal to 95 percent of the standard reference design does not comply. An ERI that merely equals Table R406.5, instead of coming in at least 5 percent less than that target, does not comply.
Read the either second. The four primary options are alternatives. The code does not invite a designer to satisfy walls from Table R402.1.3, ducts from an R405 model, and the roof from an ERI on the same house. Mandatory provisions that travel with a chosen path (testing, lighting, R405 envelope backstops, and similar) are still required by that path. They are not a license to mix primary options.
This guide teaches 2021 IECC residential provisions (first printing) as used on Exam 79. Confirm the code year on the live ICC Exam Catalog. Do not treat New Jersey energy-subcode amendments, or any other state overlay, as the national 2021 text.
Four primary options
| Path (R401.2) | Pointer | Building must satisfy | Energy packet usually contains |
|---|---|---|---|
| Prescriptive Compliance Option | R401.2.1 | Sections R401 through R404 | R-value or U-factor tables, NFRC fenestration data, air-barrier notes, blower-door and duct-leakage tests, R404 lighting, plus one R408.2 package |
| Total Building Performance Option | R401.2.2 | Section R405 | Approved performance report comparing proposed annual energy cost to the standard reference design, plus the R401.2.5 method (R408 package omitted from the proposed design, or cost ≤ 95% of reference) |
| Energy Rating Index Option | R401.2.3 | Section R406 | ERI report against Table R406.5, with the index at least 5 percent less than the table target, listed with and without on-site generation on the certificate |
| Tropical Climate Region Option | R401.2.4 | Section R407 | Demonstration that the tropical climate region applies, plus the R407 compactness, shading, ventilation, and equipment provisions |
Prescriptive work remains the stack most Exam 79 items will assume, because Building Envelope is 46 percent of the outline and the component tables live in R402. Performance and ERI do not erase those tables from the codebook; they change how envelope compliance is demonstrated. Tropical R407 is a real fourth option, not a warm-climate nickname for R405.
What each path does not authorize
Prescriptive (R401.2.1) covers R401 through R404. That includes the certificate, envelope, mechanical systems, service water heating, and lighting. Hitting the wall R-value does not excuse R404 high-efficacy lamps or duct testing. Inside R402, the applicant may use the R-value alternative, the U-factor table, or the Total UA alternative, but those are envelope methods within the prescriptive option, not a switch to R405 or R406.
Performance (R401.2.2) requires R405, not a homemade spreadsheet. The standard reference design is defined by the code. R401.2.5 then adds either an R408.2 package kept out of the proposed design, or a 95 percent annual-energy-cost cap. Modeling the efficient furnace inside R405 and counting that same furnace as the R408 HVAC package is the performance-path trap: if the R408 package is the R401.2.5 method, those measures are not included in the proposed design under R405.
ERI (R401.2.3) requires R406. Table R406.5 is the 2021 target (Climate Zone 5 is 55). R401.2.5 then requires the rated index to be at least 5 percent less than that target (55 × 0.95 = 52.25). Meeting 55 on the nose is not enough on the 2021 ERI path. Chapter 11 works the rating mechanics; this section only plants the application overlay.
Tropical (R401.2.4) requires R407 and only where the tropical climate region applies. It is not available to a Climate Zone 2 inland subdivision because a brochure says island living.
Plans-examiner documentation
Exam 79 scores envelope compliance documentation and path identification. On review, require all four of the following:
- A declared path on the construction documents. Section R103 energy data should state prescriptive, total building performance, ERI, or tropical. Mixed attachments without a declared path are not a path.
- An R401.2.5 statement. Prescriptive: which one R408.2 package. Performance: package installed and excluded from the proposed design, or the 95 percent cost demonstration. ERI: Table R406.5 target and the 5 percent reduction.
- Certificate language that will actually be posted. R401.3 requires a permanent certificate in the furnace space, a utility room, or another approved interior location. It lists predominant insulation R-values, fenestration U-factor and SHGC (largest-area value and area-weighted average when more than one value exists), duct and envelope leakage test results, heating, cooling, and water-heating types, sizes, and efficiencies, photovoltaic array data if present, ERI scores with and without on-site generation when R406 is used, the code edition, and the compliance path used. R401.2.5 independently requires the additional-efficiency option selected to be identified on that same certificate. A furnace-closet card that lists R-values but not the path is incomplete.
- Reports that match the path. A Total UA worksheet supports R402.1.5 inside the prescriptive envelope. It is not an R405 compliance report. An ERI certificate is not a substitute for R405. Reject the wrong report stapled to the right form.
Field inspection
The inspector does not re-run the rating software. The inspector confirms that installed assemblies, labels, equipment nameplates, duct locations, and test reports match the approved path. If the permit says prescriptive plus R408.2.4 ducts and air handlers entirely within the building thermal envelope, and the air handler is in an unconditioned attic, the package fails even if the cavity R-values look generous.
Scenario. A Climate Zone 5 two-story permit lists Table R402.1.3 values, a blower-door target, and LED lighting, but never names R408. Under R401.2 the file is incomplete: R401.2.5 is missing. Do not invent a package in the field. Require a revision that names one R408.2 option, or that switches the project to performance or ERI with the matching R401.2.5 method.
Scenario. Drawings stamp ERI, but the only energy sheet is a UA worksheet. UA is the R402.1.5 alternative to Table R402.1.2, not R406. Ask for the ERI report and the 5 percent reduction against Table R406.5, or have the applicant redeclare the prescriptive path.
Keep path talk independent: this is OpenExamPrep teaching of 2021 IECC residential provisions for Exam 79 study, not a claim of ICC endorsement.
A Climate Zone 5 single-family permit lists Table R402.1.3 R-values, duct-testing notes, and high-efficacy lighting, but is silent on R408 and R401.2.5. Which 2021 application rule is missing?
A builder declares the Prescriptive Compliance Option under R401.2.1. Which statement describes the primary scope of that option?
Construction documents for a dwelling outside the tropical climate region include an Energy Rating Index report and no R405 report. Which primary option has been declared?
After a passing inspection, which certificate rule from R401.2.5 must the posted R401.3 certificate satisfy?