11.2 Energy Rating Index Alternative (R406)

11.2 Energy Rating Index Alternative (R406)

Quick Answer: A 2021 ERI dwelling must meet Table R406.2 mandatories, finish at or below Table R406.5, and then beat that table by at least 5 percent under R401.2.5. Climate Zone 5's table value is 55; 5 percent less is 52.25, so a claimed integer of 55 does not pass the overlay. Without on-site renewables, proposed total UA cannot exceed Table R402.1.2 UA × 1.15 and the area-weighted SHGC in Climate Zones 0–3 cannot exceed 0.30. With renewables, the envelope must still meet 2018 IECC Table R402.1.2 or R402.1.4, renewable credit cannot exceed 5 percent of total energy use, and RECs must be documented.

Independent OpenExamPrep material for ICC Exam 79 treats R406 as a rating-file review, not a HERS marketing conversation. The index is a score against an ERI reference design. The inspector's job is to confirm that the score on the title page is the 2021 score, that the envelope backstop matches whether renewables were counted, and that the confirmed built dwelling—not only the permit model—still meets the overlay.

What ERI compliance means in R406.2

R406.2 requires the rated design to meet both of the following:

1. The sections listed in Table R406.2.
2. The maximum ERI of Table R406.5.

Table R406.2 is the mandatory stack that rating tradeoffs cannot delete. It includes R401.2.5 additional efficiency packages; the R401.3 certificate; vapor retarder; eave baffle; access-hatch retention; crawl-space wall insulation installation; air-barrier installation; envelope testing; HVAC controls; ducts under R403.3 except R403.3.2, R403.3.3, and R403.3.6; piping insulation; circulation and temperature-maintenance systems; drain-water heat recovery; mechanical ventilation; equipment sizing and efficiency; multi-family systems; snow-melt; pools and spas; lighting equipment; interior lighting controls; and R406.3 building thermal envelope. A listed section includes its relative subsections except as the table states.

R401.2.5 then tightens the index: for buildings using R401.2.3, the Energy Rating Index shall be at least 5 percent less than the Table R406.5 target. R406.5 itself requires both the rated proposed design and the confirmed built dwelling to have an ERI less than or equal to the appropriate table value when compared to the ERI reference design. After the overlay, matching the table is not enough; the confirmed house must also be at least 5 percent better than that table.

Table R406.5 — 2021 maximum ERI

Do not use 57 / 55 / 53 as the 2021 table. Those figures belong to older editions and stale study sheets. Climate Zone 4 is 54, Climate Zone 5 is 55, and Climate Zones 7 and 8 are 53.

Worked overlay: Climate Zone 5

Table R406.5 lists 55 in Climate Zone 5. Five percent of 55 is 2.75. "At least 5 percent less" means the rated ERI must be at or below 55 − 2.75 = 52.25. An integer score of 55 is a 0 percent reduction. An integer score of 53 is only (55 − 53) / 55 = 3.6 percent less. An integer score of 52 is (55 − 52) / 55 = 5.45 percent less, which satisfies "at least 5 percent less." Teach the arithmetic that way on Exam 79: 55 × 0.95 = 52.25, so a claimed passing integer of 55 (or 53) fails the overlay. If the score is reported as a whole number, treat 52 as the integer that clears 52.25. The confirmed built dwelling must meet the same reduced target, not merely the permit model.

R401.3 then requires the posted certificate to list the ERI with and without on-site generation when an ERI is determined.

Envelope backstop — Equation 4-1 versus the 2018 floor

R406.3 sends the envelope to R406.3.1 or R406.3.2.

On-site renewables are not included (R406.3.1). Proposed total building thermal envelope UA—the sum of U-factor times assembly area—shall be less than or equal to the UA built from Table R402.1.2 U-factors multiplied by 1.15, Equation 4-1. In Climate Zones 0 through 3, the area-weighted maximum fenestration SHGC is 0.30. A UA worksheet that uses 2021 Table R402.1.2 with no 1.15 product, or that allows SHGC 0.40 in Climate Zone 2 on an ERI house without renewables, is the wrong backstop.

On-site renewables are included (R406.3.2). The building thermal envelope shall be greater than or equal to the levels of efficiency and SHGC in Table R402.1.2 or Table R402.1.4 of the 2018 IECC. Renewables do not authorize a 2006-level wall. They change which historic table is the floor.

How the index is calculated (R406.4)

The ERI shall be determined in accordance with RESNET/ICC 301, except that for buildings covered by the International Residential Code the ERI reference design ventilation rate shall follow Equation 4-2:

Ventilation rate (cfm) = (0.01 × CFA) + 7.5 × (N_br + 1)

where CFA is conditioned floor area in square feet and N_br is the number of bedrooms. A 301-only ventilation rate that ignores Equation 4-2 on an IRC dwelling is not a 2021 IECC ERI.

Energy used to recharge or refuel a vehicle used for transportation on roads that are not on the building site shall not be included in the ERI reference design or the rated design. For compliance purposes, any reduction in energy use of the rated design associated with on-site renewable energy shall not exceed 5 percent of the total energy use. A file that drives the index from 70 to 48 entirely with rooftop PV, without that 5 percent cap, is not a compliance ERI.

Who verifies what

R406.6 splits the inspection work. Verification of compliance with R406 as outlined in R406.5 and R406.7 shall be completed by an approved third party. Verification of compliance with R406.2 shall be completed by the authority having jurisdiction or an approved third-party inspection agency (R105.4). The rater who produced the index does not automatically satisfy the AHJ's Table R406.2 punch list. The AHJ still confirms mandatories: testing, lighting, certificate, and the R406.3 envelope backstop.

Software, reports, and RECs

R406.7.1 requires Approved Software Rating Tools in accordance with RESNET/ICC 301. A desktop spreadsheet is not a rating tool.

R406.7.2 requires a proposed compliance report with the permit application and a confirmed, site-specific report before the certificate of occupancy. Both reports declare ERI on the title page and on the building plans, name the analyst and the software version, document inputs, and carry a certificate of component specifications. The permit certificate uses assumed duct and envelope leakage; the confirmed certificate uses tested results and installed efficiencies. Where a site-specific proposed report is not generated, worst-case orientation and configuration apply—the same discipline as R405.

Where on-site renewable energy is included in the ERI, R406.7.3 requires one of the following:

1. Substantiation that the renewable energy certificates (RECs) associated with the on-site renewable energy are owned by, or retired on behalf of, the homeowner; or
2. A contract that conveys those RECs to the homeowner, or conveys an equivalent quantity of RECs associated with other renewable energy.

A solar array that sold its RECs to a utility, with no replacement contract, cannot be counted in the compliance ERI. R406.7.4 lets the code official demand reference-design characteristics, a builder-signed certification of the rated design, and the actual software inputs. Unspecified inputs come from RESNET/ICC 301 (R406.7.6).

Scenario: Climate Zone 5 ERI of 55 called passing

A Climate Zone 5 permit stamps "ERI 55 — complies with Table R406.5." The rater's cover letter quotes the table and stops. Under R401.2.5 the index must be at least 5 percent less than 55. 55 × 0.95 = 52.25. An ERI of 55 is the table value, not a 5 percent reduction. Reject the file until the rated design—and later the confirmed built dwelling—shows an ERI at or below 52.25 (in practice ≤ 52 if the score is reported as a whole number). Do not accept "55 is the 2021 Climate Zone 5 number" as a substitute for the overlay.

This is independent OpenExamPrep teaching of 2021 IECC residential provisions for Exam 79 study, not a claim of ICC or RESNET endorsement.