Updated IECC Residential Energy Guidelines Released

The last time the IECC Compliance Guides were updated was 2018. These guides are energy code compliance aids based on state energy data, regional climate zones as well as improvements made in the industry.

In October 2020, the IECC hosted their annual convention to discuss the upcoming changes to their energy-saving guidelines on residential windows, doors and skylights.

Adjusted Climate Zone Regions

No new climate zones were created with the 2021 update, but a handful of counties changed zones. The majority of the counties that changed, were being moved to milder climates. Counties that are reassigned to milder zones have generally less stringent code requirements, although not by much.

Of the 23 counties that moved into a colder climate zone, over half of them were from Oklahoma. They were moved from zone 4 to zone 3.

2021 Changes: Windows

The most impactful changes in 2021 come in the form of adjusting zone 2’s recommended U-factor from 0.40 to 0.35, becoming more stringent. The same was done for zones 3 and 4 (not marine), where the suggested U-factor went from 0.35 to 0.32.

There was only one change with Solar Heat Gain Coefficient (SHGC) suggestions, in which zone 4 (marine) and 5 went from NR to 0.40, which is more stringent. This brought these two climate zones into the same recommended range as the non-marine parts of zone 4.

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