IECC Climate Zone Guides
Attic insulation targets, seasonal risks, and example cities for every US climate zone from Zone 1 through Zone 8.
Very Hot (South FL, HI)
Zone 1 homes deal with extreme cooling demand, solar gain, and long air-conditioning seasons.
Hot (TX, FL, AZ)
Zone 2 still skews cooling-dominant, but homes also need enough attic depth to control shoulder-season heat flow.
Warm (South US)
Zone 3 homes need balanced performance because they face both muggy summers and meaningful winter heat loss.
Mixed (Mid-Atlantic)
Zone 4 is a classic mixed climate where attic upgrades can improve both winter comfort and summer stability.
Cold (North/Midwest)
Zone 5 homes are heating-driven and often see strong payback from attic upgrades because winter losses are substantial.
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.
Subarctic
Zone 7 is extremely cold, so attic insulation quality has outsized influence on comfort, durability, and heating cost.
Arctic (AK)
Zone 8 homes are in arctic conditions where attic mistakes are expensive and durability issues show up quickly.
Build a Better Attic Plan
See what matters most in hot climates where attic heat gain and duct losses drive comfort.
Focus on cold-climate attic priorities such as depth, air sealing, and ice dam prevention.
Learn how ventilation details can help or hurt an attic insulation retrofit.