The 2015 IECC/IRC add an additional path to energy code compliance using an Energy Rating Index (ERI). The ERI scale ranges from 0, to represent net zero energy, to 100, which represents the approximate efficiency of a home built to the 2006 IECC. Each point on the ERI scale represents a 1-percent change in the relative energy efficiency of the building. Each point higher is 1-percent less efficient and each point lower is 1-percent more efficient.
By design the ERI is intended to be more stringent than the Prescriptive, or Performance Paths, due to trade-offs of shorter-lived measures for permanent energy efficiency.
ERI allows the use of the insulation and fenestration efficiency values in Table 402.1.1 or 402.1.3 of the 2009 IECC instead of the equivalent tables in the 2015 IECC as long as the difference in efficiency is made up in other areas, including installed appliances, water heating and HVAC systems. Trading off long lasting envelope efficiency measures for short term measures like HVAC creates a long term energy efficiency deficit. ERI attempts to deal with this issue by making the initial ERI score lower or more efficient than a purely prescriptive score would require. This increases the odds that the building’s life cycle energy efficiency will not be too badly reduced.
To meet compliance using the ERI Path, a residential building must achieve an ERI score equal to or less than the maximum ERI score (discussed below) as well as meet all of the mandatory provisions of the 2015 IECC/IRC, and the building thermal envelope must be equal to or better than the levels of insulation and Solar Heat Gain Coefficient in Tables 402.1.1 or 402.1.3 of the 2009 International Energy Conservation Code.
The ERI does not include on-site power production such as solar PVs.
The published IECC contains the following maximum ERI Scores for the climate zones in Texas and Oklahoma.
The Texas Legislature, through House Bill 1736, specified the Texas ERI Maximum Score and established a gradual improvement over the next 6 years. Those maximum scores and time frames, which are now in statute, are contained in the table below.
State law authorizes local jurisdictions to implement and enforce the energy code, and the maximum ERI scores may be amended by local jurisdictions as they adopt the 2015 IECC/IRC energy code. ERI scores can vary greatly because of differences in climate zone, building size and other variables.
Below we provide charts of cities showing the variations of ERI scores by size and whether they are all electric or gas/electric. The ERI score adopted by a local jurisdiction should be low enough for 90% of all homes to be more efficient than the prescriptive code, otherwise less efficient homes will be built using this alternative path, and similar energy savings will not be realized by its residents.
Click on the links below for ERI scores by size and code for individual cities in Texas.
| Amarillo | Houston |
| Austin | Laredo |
| Corpus Christi | Lubbock |
| Dallas/Ft. Worth | Midland |
| Del Rio | San Antonio |
| El Paso |
[1] The 2015 IECC and 2015 IRC Residential Energy Codes are now aligned and equivalent, so either can be adopted.
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