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Building Science

The 2015 IECC Recognizes Home Energy Ratings

With a specific HERS Index for each climate zone, the new energy code provides home builders with an alternate compliance path

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The 2015 IECC will include a compliance path for home builders to demonstrate that their homes meet the energy code by getting a home energy rating. The home's HERS Index must meet the threshold requirement for the home's climate zone.
Image Credit: Energy Vanguard
The 2015 IECC will include a compliance path for home builders to demonstrate that their homes meet the energy code by getting a home energy rating. The home's HERS Index must meet the threshold requirement for the home's climate zone.
Image Credit: Energy Vanguard
The HERS Index scale shows how energy efficient a home is. Lower numbers are better, and an Index of 100 means the home just meets the 2004 IECC requirements.
Image Credit: RESNET

Great news, everyone! (If you read that in the voice of Professor Hubert Farnsworth, please don’t let your imagination run away with you. This really is great news.) The HERS Index will part of the 2015 International Energy Conservation Code. Why does that matter?

Because it will help home builders build better homes.

Because it explicitly states what HERS Index is needed for each climate zone.

Because more home buyers will know what kind of performance to expect.

A coalition of groups has been pushing a proposal to use the HERS Index, and just this week, the International Code Council adopted it, with some modifications. The groups include RESNET, Natural Resources Defense Council, Air Conditioning Contractors of America, Leading Builders of America, and Institute for Market Transformation.

The HERS Index thresholds

Here’s the HERS Index that each climate zone (CZ) must meet:

  • CZ 1 & 2                  52 
  • CZ 3                        51
  • CZ 4                        54
  • CZ 5                        55
  • CZ 6                        54
  • CZ 7 & 8                  53

Yeah, those are pretty low numbers, but the 2015 IECC takes another big step toward energy efficiency in every path. They’re lower than NRDC and the other groups had proposed, too.

For more background on this change, here are a few resources that go into the details of the proposal. There’s not a lot of news out yet about the actual code change.

David Goldstein’s article in the NRDC blog

Factsheet on adding the HERS Index compliance path

Energy Efficiency Wins Big in New Residential Building Codes – press release from the Institute for Market Transformation (10/10/13)

How is this different from the current performance path?

The performance path has been in the energy code for a while now. It’s used in the 45L tax credit for new homes, for which home builders have to show that the homes they’re trying to qualify use at least 50% less energy than the 2006 IECC requires and then get $2,000 if they make it.

The performance path in versions of the IECC up to 2012, however, specifies neither a HERS rating nor a HERS Index. It’s based on annual energy costs. The proposed design has to have lower energy costs than the standard reference design, which is specified in the code. (See section 405 in the IECC.) It’s also limited to the energy used for heating, cooling, and water heating only. Lights and appliances are not included.

The new compliance path requires that a home meet a certain HERS Index. That means that lights and appliances count, too. And with Indices of 51 to 55, the energy savings will be considerable. Homes being built to the 2009 IECC probably have a HERS Index in the 80s. The HERS Index scale is based on the 2004-06 IECC, with 100 being the HERS Index of a home that just meets that version of the code.

For a full explanation of the HERS Index, see my article, Everything You Ever Wanted to Know about the HERS Index.

What will this mean?

It remains to be seen how much this will really affect the energy efficiency of homes. Dr. Goldstein makes the case that it will save billions of dollars, writing, “Our proposed 2015 update will accumulate to a national cost savings of over $100 billion by 2030 compared to the 2006 code.” I think that’s a bit of hyperbole because the savings generated by this new compliance path will come from builders using it rather than one of the other paths in the 2015 IECC. Anyone on that code will be building much more energy-efficient homes compared to the 2006 IECC.

Still, it’s a great option. In the state of Florida, most builders use the compliance path and hire HERS raters. Before we know what will happen with this new path, I think we need to see what’s going to happen to answer these questions:

  • How many states will adopt the 2015 IECC?
  • How many builders in the states that adopt the 2015 IECC will go the HERS Index route?

However things develop, I think it’s great news that we’ll at least have this as an option, explicitly spelled out in the 2015 IECC.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


  1. user-946029 | | #1

    For more info...
    The Green Builder Coalition also backed the ERI proposal, but we backed the one approved by the Dallas committee (also known as the original, with the stronger ERI scores) and confirmed by the voting members.

    You can read a detailed summary of the two main IECC-R debates, written by myself and our Advocacy Director, here:

    And you can also find a good recap from Meg Waltner (NRDC proponent who delivered testimony) here:

  2. Donnygo | | #2

    Note to say Hello
    New to this site and checking out the articles. About the Authors, has an impressive set of credentials and I expect to find things of interest. I am a retired home owner interested in ‘where we are going,’ and hoping for better. I’m hoping someday to obtain a PHD in common sense. Good Luck with this site, Don

  3. Nick Sisler | | #3

    Another big step in every path?
    Allison, just a question about this statement: 'the 2015 IECC takes another big step toward energy efficiency in every path.'

    As I read 2015, the prescriptive and performance paths look about the same as 2012. Is there something I'm missing?

  4. user-946029 | | #4

    DoE Determination

    The DoE did a preliminary determination on the 2015 IECC, and found it was approximately 1% more efficient than the 2012 IECC.

    A well-respected energy efficiency expert told me the 2012 envelope is just about as good as you can get without going all-out bonkers. I think future efficiency gains are going to have to come from some other area.

    Where? With a goal of net-zero code built homes by 2020, I'd look to CA's Building Energy Efficiency Standards (BEES). Their latest version (2013) went into effect July 1, 2014. Scheduled to be updated every 3 years, they are already going through their 2016 version. On that timeline, it will be released in 2017 and will be the version just prior to the 2020 (i.e., net-zero) BEES.

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