IECC Climate Zone Guides

Attic insulation targets, seasonal risks, and example cities for every US climate zone from Zone 1 through Zone 8.

Zone 1R-30

Very Hot (South FL, HI)

Zone 1 homes deal with extreme cooling demand, solar gain, and long air-conditioning seasons.

Example cities: Miami
Zone 2R-38

Hot (TX, FL, AZ)

Zone 2 still skews cooling-dominant, but homes also need enough attic depth to control shoulder-season heat flow.

Example cities: Phoenix, Houston
Zone 3R-38

Warm (South US)

Zone 3 homes need balanced performance because they face both muggy summers and meaningful winter heat loss.

Example cities: Atlanta
Zone 4R-49

Mixed (Mid-Atlantic)

Zone 4 is a classic mixed climate where attic upgrades can improve both winter comfort and summer stability.

Example cities: New York, Seattle
Zone 5R-49

Cold (North/Midwest)

Zone 5 homes are heating-driven and often see strong payback from attic upgrades because winter losses are substantial.

Example cities: Chicago, Denver, Boston
Zone 6R-49

Very Cold (Northern US)

Zone 6 requires thick attic coverage because long winters and deep temperature swings expose every weak spot in the ceiling plane.

Example cities: Minneapolis
Zone 7R-49

Subarctic

Zone 7 is extremely cold, so attic insulation quality has outsized influence on comfort, durability, and heating cost.

Example cities: none in the current city set
Zone 8R-49

Arctic (AK)

Zone 8 homes are in arctic conditions where attic mistakes are expensive and durability issues show up quickly.

Example cities: none in the current city set
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