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Pathways to Energy Compliance

Residential Energy Compliance Paths

When building a new residence, choosing an energy-efficient home design is important. Ensuring compliance with the International Energy Conservation Codes is mandatory. However, it can be a challenging and confusing process, especially as you move between various municipalities. This document is being provided to offer clarity on the primary residential energy compliance pathways.

International Energy Conservation Code (IECC) – Chapter 4 [RE] Residential Energy Efficiency

The intent of the IECC residential provisions is the effective use and conservation of energy over the useful life of the building (IECC Section R101.3), and within the 2015 and 2018 IECC there are three distinct compliance options — typically referred to as the prescriptive, performance and energy rating index (ERI) paths. The code user may consider each of the options and determine which is the best for them. However, one option must be used in its entirety, a user cannot pick different compliance options for different parts of the building. This document provides clarification of the similarities and differences between the three paths and highlights the compliance issues to verify.

Section R401.2 of the IECC identifies three compliance paths or options. They are listed below with their common names.

  • Sections R401 through R404 of the IECC (commonly called the prescriptive path).
  • Section R405 and the provisions of Sections R401 through R404 of the IECC indicated as “mandatory” (commonly called the performance or simulated performance path).
  • The energy rating index approach in IECC Section R406.

When conducting a residential plan review or inspection it is critical to know which compliance path was chosen. Not only do the requirements differ, so do the compliance tools. An essential verification process, applicable to any compliance path, should include verifying:

  • The project information matches the information on the building plans.
  • The levels of efficiency (insulation, windows and doors) shown on the plans and onsite meet or exceed that shown in the documentation.
  • The correct ceiling, wall and floor components that define the building envelope are shown on the plans and onsite.
  • Air leakage testing.
  • The Manual J or other engineering calculations required in IECC Section R403.7 are provided and match the inputs match values on the plans and in the compliance documentation.

Prescriptive

The prescriptive compliance path requires no software or modeling. It can be verified via a checklist. It requires, quite simply, complying with (as applicable to the building) the provision of IECC Section R401 General, Section R402 Building Thermal Envelope, Section R403 Systems, and Section R404 Electrical Power and Lighting Systems. Using the prescriptive path, one must simply comply with the items listed as prescriptive or mandatory in IECC Sections R401 through R404. This makes the prescriptive code fairly simple to follow. However, it does not give builders credit for any of the additional efficient practices that they may incorporate into their buildings, improved diagnostic testing results, or mechanical systems or domestic appliances that are more efficient than the federal minimums.

Jurisdictions may wish to provide applicants with a prescriptive checklist form tailored to the local climate zone. A checklist form can be used to verify compliance during both plan review and inspection. Verification may be limited to the essentials noted above.

Chapter 4 [RE] Residential Energy Efficiency – Section R402.1

  • This method is the most straightforward as each building material must meet the minimum envelope requirements. The downside to this method is that it does not provide any credit for additional efficient practices that have been incorporated into the building – such as appliances that are more efficient than federal minimum requirements.
  • To comply, the building thermal envelope must meet the requirements per climate zone as listed in Table R402.1.2.

Total UA Alternative

Within IECC Section R402 Building Thermal Envelope there is the optional total UA (sum of U-factor times assembly area) alternative — IECC Section R402.1.5 — which offers a tradeoff of lower performance building envelope assemblies with higher performance assemblies. This option only allows for envelope tradeoffs; none for mechanicals, performance testing or anything else. Compliance may be calculated by hand in accordance with the ASHRAE Handbook of Fundamentals, or by using the free United States Department of Energy software RESCheck, which may be downloaded here. When applicants submit with REScheck compliance documentation, a separate form is not needed, the REScheck generated forms will provide the information needed for plan review and inspection. Table 402.1.2 of the IECC is no longer applicable when using the UA alternative. In addition to the essential items listed above, it will be important to verify:

  • The project complies with the applicable code. The maximum UA must be greater than or equal to the proposed design UA to demonstrate compliance.
  • The gross area or perimeter and window areas values represent the proposed design.
  • The correct ceiling, wall and floor components that define the building envelope are shown.

Chapter 4 [RE] Residential Energy Efficiency – Section R402.1.5

  • Allows for greater flexibility in terms of trade-offs. If the total U-Factor is equal to or less than what would’ve been achieved using the prescriptive method the building is within compliance.
  • If the total building thermal envelope UA (sum of U-factor times assembly area) is less than or equal to the total UA resulting from using the U-factors in Table R402.1.4 (multiplied by the same assembly area as in the proposed building), the building shall be considered in compliance with Table R402.1.2. The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The SHGC requirements shall be met in addition to UA compliance.
  • This alternative allows one portion of the building to make up for another. It recognizes that there may be reasons for less insulation in some parts of the building, which can be compensated for by more insulation in other parts of the residence. The key concept is that the overall building thermal flow (UA) meets the code. This concept could allow a ceiling to make up for a wall or vice versa. As a practical matter, whether a building will comply by this method can sometimes be estimated quickly. A large area that is significantly over the required R-value will make up for a small area only mildly under the required R-value.

Performance Based Complianc

The performance path, or compliance option, provides code users with greater flexibility through using computer simulation to demonstrate that the proposed design would have the same or less than the same energy as the “standard reference design” building. Section R405 of the IECC details the protocol for demonstrating compliance. As noted in IECC Sections R401.2(2) and R405.2, the proposed design must include all applicable requirements labeled “mandatory” in IECC Sections R402 through R403 — these are design elements that cannot be traded off. Energy for lighting and appliances is not included in this path, and mechanical system efficiency is normalized between the proposed and standard reference designs.

Chapter 4 [RE] Residential Energy Efficiency – Section R405

  • Similar to the U-Factor alternative method but instead of using U-Factor improvements you can trade off lower insulation levels in the building for energy improvements such as geothermal and solar systems.
  • Compliance based on simulated energy performance requires that a proposed residence be shown to have an annual energy cost that is less than or equal to the annual energy cost of a standard reference design.
  • Compliance software tools are used to generate a compliance report (Section 405.4.2) validating that the proposed design annual energy cost is equal to or less than that of the standard reference design.

Energy Rating Index (ERI)

The Energy Rating Index was introduced as Section R406 of the 2015 IECC. In 2018, the IECC language was simplified by referring to ANSI/RESNET/ICC Standard 301, and other modifications were made, but the scope of the compliance path did not change.

Table R406.4 of the IECC provides the maximum allowed ERI score based on climate zone. Note, whereas in IECC Section 405 the simulated performance option uses values from construction documents that can be verified in the field, the ERI is not calculated until values have been field verified and appropriate tests are conducted.

These elements are verified in the field, an assessment of insulation installation is conducted, building and duct air leakage is determined, and the gathered information is used to calculate an ERI by comparing the efficiency of this constructed design to an ERI reference design.

In addition to the essential verification items listed above, it will be important to verify:

  • The compliance documentation indicates the ERI of the proposed design is less than or equal to that referenced in IECC Table R406.4.
  • The building thermal envelope is equal to or greater than the levels of efficiency and solar heat gain coefficient in Tables 402.1.1 or 402.1.3 of the 2009 IECC (or 2015 IECC when on-site renewable contributes to the ERI score).
  • The proposed design includes applicable mandatory requirements from IECC Sections R401 through R404.

Chapter 4 [RE] Residential Energy Efficiency – Section R406

  • This method allows for alternative routes to compliance. You can compensate with more energy efficiency in alternative areas of a home unrelated to the building envelope.
  • An ERI is a measurement of a residential building’s efficiency based on a comprehensive list of building criteria — such as assembly types, geometry, orientation, solar heat gain coefficient, insulation and efficiency levels, lighting, and appliances (including those not addressed in IECC Sections R401 through R405, such as washers and dryers), fans, service water systems, thermal storage, and whole-house mechanical ventilation elements — from the construction documents
  • An ERI is calculated comparing a residential building to the standard reference design, which is aligned with the 2006 IECC. Compliance documentation will provide an ERI value typically between 100 and zero. Where the energy performance of the actual building and the ERI reference building are equal, the ERI is 100, and where the actual residential building requires no net purchased energy annually, the ERI is zero.
  • The use of an approved software is required to show that the home is equal to or more energy efficient when compared to following the prescriptive path.

LAST UPDATED:November 17th, 2023

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