A Simplified Explanation of the International Energy Conservation Code (IECC)

EnergyLogic is a residential energy services company that specializes in energy code and/or program compliance, generation of the HERS® or ERI index score, third-party risk and quality assurance inspections and diagnostics, as well as HVAC design. Most often we work directly with architects, builders, and developers and it begins with code compliance. This article will focus on explaining the International Energy Conservation Code (IECC).

The IECC is a tool used by jurisdictions to ensure that when new or remodeled homes are built, they achieve a specific quantifiable level of energy efficiency. Although it is a code, it does not mean that it is one-sided. In other words, the energy code is a marvel of flexibility, offering multiple compliance paths in order to help determine the most cost-effective way to build a home that not only meets the performance goals and expectations of our modern world but also includes the design imagination and material integration we desire. Yes, there are boundaries to this game, but there is flexibility as well, to ensure that we can build and live in the homes of our dreams.

Energy code flexibility is discovered in the different compliance paths of the code. A path through the energy code guides one through a series of code sections that, when followed, demonstrate that a building’s design meets the baseline requirements of the code defined by a quantifiable amount of energy use in the home. The quantifiable amount of energy used in a home is defined by a reference home, which the home you want to build is compared to.

What is a reference home?

Imagine your two hands are two homes that are geometric twins of each other. Your left hand, the reference home, is a house built with the energy and aesthetic features defined by the code which uses a quantifiable amount of energy that the code has deemed to be the minimum amount allowed by the jurisdiction.  Your right hand is the home you want to build, the proposed design, with the energy and aesthetic features you believe, are best to achieve whatever goal you have for the home: cost- effectiveness, safety, aesthetic beauty, comfort, durability, efficiency or livability.  Your home, the proposed design, on the right, is compared to the code reference home on the left and if your home’s performance is equal to or better than the reference home it complies with the code and can be permitted to be built.  The jurisdiction, an approved third-party, or both will inspect, verify, and report that the home was built as proposed in order for the certificate of occupancy to be released. 

Important terminology to know:

Mandatory requirements– requirements that must be met in every building design no matter which compliance path is chosen, unless there is a specific exception in the code

Prescriptive requirements – Requirements that must be met by every building, unless an approved tradeoff is utilized or unless there is a specific exception in the code

Tradeoffs – tradeoffs are defined performance features in a home such as R-values, U-values, infiltration, or duct leakage that allow trades to be made between various low and high performing features of a home

Performance approach – An overall performance requirement for the building that replaces the individual prescriptive requirement for building systems and components

Pathways in the IECC

There are four basic pathways through the code, all of which utilize the reference home/proposed design construct described above. The primary difference between the paths is ease of use and flexibility of choice of materials to determine the most cost-effective way to achieve the efficiency goals of the code and the builder.

Prescriptive Path:

The prescriptive path lays out the energy specification, R-values, and U-values, as well as installation techniques that must be used in the home you want to build. If you choose the prescriptive specification level for your home, you must install materials that are equal to or better than those listed in the R-value or U-value tables in the code in order to achieve a level of performance that is equal to or better than the reference homes level of performance.

Area weighted U-value or UA trade-off path (sometimes called the RESCheck Path):

RESCheck is not a compliance path: it is actually a software developed by the Department of Energy to demonstrate Area Weighted U-value (UA) trade off compliance. The pathway uses a tradeoff approach which provides flexibility for builders and designers to determine how they want to create a house.  For example, if a builder wants to install R-38 insulation in an attic rather than the required R-49 as prescribed by the 2015 IECC in climate zone 5, they may be able to trade off the lower energy performance in the attic for better than prescribed energy performance somewhere else in the home, such as foundation insulation.  In this way, the builder has demonstrated that lower R-value performance in the attic can be traded off for higher R-value performance on the foundation.

Simulated performance path:

The simulated performance path builds on the UA method and utilizes whole-house energy analysis to determine compliance with the IECC. As energy moves by conduction, convection, and radiant energy transfer this path offers the most flexibility by not only utilizing R-value and U-value tradeoffs but also allowing tradeoffs of house tightness and duct leakage, among other things. Annual energy costs rather than area weighted U-value is used as the matrix of compliance. In other words, the proposed design’s annual energy cost must be lower than or equal to the code reference home, to demonstrate compliance. Currently, EnergyLogic believes that the Simulated Performance path is the path that best helps builders achieve the most cost-effective and high-performance home to meet the intent of the IECC.

Energy Rating Index (ERI) path:

The Energy Rating Index and the HERS Index are the same. However, the ERI score is used as part of a code compliance path that was adopted in the 2015 IECC. It is important to know that the climate zone specific ERI score is one, but not the only thing required by the pathway. Like all code paths, the ERI path requires that all mandatory features of the code be completed for each home.  In addition, among other things, features such as mechanical equipment and solar, can lower the ERI score; therefore, in order to ensure a sound thermal envelope, a backstop was introduced. A home using the ERI path must use the prescriptive insulation levels outlined in table R402.1.1 of the 2009 IECC.

The 2018 IECC kept the structure of the ERI path while raising the ERI scores in each climate zone. In addition, if solar is installed on a home, the 2018 IECC states that the prescriptive insulation levels outlined in table R402.1.2 of the 2015 IECC must be used.

Robby Schwarz (faked)

Who to Contact:

Robby Schwarz
Principal, Director of Builder Relations

Email Robby

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