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How Climate Zones Affect Building Codes

Climate Zones and Building Codes

Across the United States and the world there are various climates that affect how cold or how much moisture there is in a particular region, but what is less understood is how these climate zones also affect building codes. Codes have been put in place to provide minimum requirements for new building designs and additions. The International Energy Conservation Code (IECC) places building codes regulating the exterior envelope of a building and their selection of air conditioning, ventilating, heating, service water heating, electrical, and equipment for effective use of energy. Different regions of the United States have been mapped to show their climate zones below:

Climate zones.

Heating and cooling degree days are used to determine which climate zone a region is in. Degree days are calculated as the difference in temperature between the average temperature of the day (high plus low temperature divided by two) and 65oF. As seen, Montana is fully covered by Zone 6B, 6 meaning cold and B meaning dry.  A cold climate zone is a region that experiences between 7200 and 9000 heating degree days per year (on a 65oF basis) whereas in regions like Florida, they have between 6300 and 9000 cooling degree days. The number of cooling and heating degree days affect codes for different regions. Shown below are maps representing the heating and cooling degree days across the United States. Specifically, southwest Montana and northwest Wyoming are among the highest heating degree days and lowest cooling degree days.

Annual Average Cooling and Heating Degree-days (1901-2000)

Annual average cooling and heating degree-days.

As for building in those specific climate zones, it is important to have proper designs. For example, homes in cold humid climates require the vapor barrier to be placed on the inside of the insulation to prevent rot whereas homes in warm climates require the vapor barrier on the outside of the insulation. Specifically in Montana, the code for above ground exterior walls requires insulation of R-21 and R-49 for ceilings. Some buildings though require more insulation based on shading and passive solar gain a house receives. In extreme climate regions like Big Sky, Montana, it is important to go above and beyond what a state-wide code requires to ensure sustainable and energy efficient building.

For further information on how climate zones affect building codes in Montana, please reach out to Cornerstone Management Services today. 



Written by:

Ward Cereck – CMS Engineering Intern 

Edited by:

Paul Williamson – CMS Director of Business Development



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