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Building Codes – Get Into the Zone

Building codes provide the minimum requirements for what all builders have to do (in order to follow the law, that is) when constructing and maintaining buildings.The variances between building codes in different states or even different regions within states has everything to do with one main consideration – the climate.

Climate has a significant impact on building codes, energy codes in particular.

What makes perfect sense for good moisture management in one climate varies wildly from that of another region.  It can even be quite different within one state. California is the most varied state – Marine, Hot-Dry, Mixed-Dry, and Cold. Builders really have to understand the particular climate they’re working with in order to follow good building science principles.

ICC Climate Zone Map

Surprisingly, prior to 2004 there was no universal climate zone map for the U.S. for use with building codes. At that time, ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) used 38 different climate groupings, while the IECC used 33 different zones based on county boundaries. That’s a lot of climate chaos.

Recognizing the need for an easier way to define climate, researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory (in conjunction with Building America) prepared a simplified map, and the 2004 IECC Supplement was the first model energy code to adopt this new climate zone map (map from ICC shown above).

Temperature & Humidity

Temperature and humidity are the two primary factors that influence the 8 climate zones in the U.S. Each of the eight zones are further divided into five climate “categories”:

  • 8  Subarctic  (Alaska only)
  • 7  Very Cold
  • 6  Cold
  • 5  Cold
  • 4  Mixed Humid or Mixed Dry
  • 3  Hot-Humid or Hot-Dry (some Marine)
  • 2  Hot-Humid or Marine
  • 1  Hot-Humid

If you’re a true building science guru, you’ll want to better understand something called “degree days”, or accumulated temperature calculations. The Energy Vanguard Blog has an excellent piece by building science expert Allison Bailes III, that dives deeper into temperature and moisture divisions.

Climate-Based Resources for Builders 

Considering that several states are in multiple climate zones, the DOE Building Best Practices Series issued the “Guide to Determining Climate Regions by County”, a helpful resource for builders listing every county within that state, and which climate category to follow in each county.

There are multiple climate-based Best Practices guides available for builders through the DOE Building America Program, which focus on real-world case studies that demonstrate solutions to improve whole-house energy performance for new and existing homes in the five major climate regions.

For a direct link to these climate-based case guides for all climates, visit energy.gov.  

The DOE Building TechDOE Building America logonologies Program works to improve the energy efficiency of buildings in the U.S. through educating builders on better building practices, and technological advancements in materials and techniques. Energy-Star and Zero-Energy Ready are just a a few of their recognizable efforts in place and on track to meet significant goals by 2020.  



  1. Thanks for helping me learn more about building codes. It’s good to know that two of the most primary factors that influence the climate zones are temperature and humidity. I’m kind of interested to learn more as to how the design of the building would be affected by the humidity of the area.

  2. ThermalBuck says:

    You’re welcome! Good resources on building science are becoming much more readily available, making it easier to find information related to how your building will “function” in your specific climate. It really impacts your building material choices, and wall assemblies. Some good resources in this post, and social media is also a valuable resource – find good accounts to follow for your specific region. Let us know where you’re located, and we will try to point you to good information. Humidity is a huge issue – moisture is the number one cause of building failures, and remediation is expensive.

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