Find your climate zone
The IECC divides the US into seven climate zones, from Zone 1 in southern Florida and Hawaii to Zone 7 in northern Minnesota and Alaska. Your zone determines how much insulation is worth installing.
Hover or select a state on the map — or enter a ZIP code — to see the recommended R-values for that climate zone.
Zones follow the IECC climate zone map. Each state is shown in its most populous zone; nine states span three or more. For a precise answer, use the ZIP lookup or check with your local building department.
All seven zones
Cooling runs nearly year-round; heating is almost irrelevant.
- Attic
- R-49
- Walls
- R-13
- Floor
- R-13
Miami, FL · Key West, FL
Zone 1 guideLong cooling season, short mild winter.
- Attic
- R-60
- Walls
- R-13
- Floor
- R-13
Houston, TX · Phoenix, AZ
Zone 2 guideWarm, with short mild winters and a real cooling season.
- Attic
- R-60
- Walls
- R-20
- Floor
- R-19
Atlanta, GA · Dallas, TX
Zone 3 guideMeaningful heating and cooling seasons, roughly balanced.
- Attic
- R-60
- Walls
- R-20
- Floor
- R-25
Washington, DC · Nashville, TN
Zone 4 guideCold winters dominate; heating is the main load.
- Attic
- R-60
- Walls
- R-20
- Floor
- R-30
Chicago, IL · Denver, CO
Zone 5 guideLong, cold winters with a short cooling season.
- Attic
- R-60
- Walls
- R-21
- Floor
- R-30
Minneapolis, MN · Burlington, VT
Zone 6 guideSevere winters. Maximum insulation is clearly cost-effective.
- Attic
- R-60
- Walls
- R-21
- Floor
- R-38
Duluth, MN · Fargo, ND
Zone 7 guideRecommended R-value by zone
| Zone | Attic | Walls | Floor | Crawl walls | Example city |
|---|---|---|---|---|---|
| Zone 1 | R-49 | R-13 | R-13 | — | Miami, FL |
| Zone 2 | R-60 | R-13 | R-13 | R-10 | Houston, TX |
| Zone 3 | R-60 | R-20 | R-19 | R-15 | Atlanta, GA |
| Zone 4 | R-60 | R-20 | R-25 | R-15 | Washington, DC |
| Zone 5 | R-60 | R-20 | R-30 | R-19 | Chicago, IL |
| Zone 6 | R-60 | R-21 | R-30 | R-19 | Minneapolis, MN |
| Zone 7 | R-60 | R-21 | R-38 | R-19 | Duluth, MN |
How climate zones are set
Zones are defined by the International Energy Conservation Code, primarily from heating and cooling degree days — a measure of how far and how long local temperatures sit away from a comfortable baseline. They are assigned by county, not by state.
That matters because altitude shifts zones as much as latitude does. Flagstaff, Arizona is Zone 5 while Phoenix, three hours south, is Zone 2. Our map colors each state by its most populous zone, which is right for most people and wrong near boundaries and at elevation.
The calculator uses the same approximation and lets you override it. If your result looks off for where you live, change the zone manually — the target R-value follows immediately.