Connecticut Climate Zones by County
All eight of Connecticut's counties are in climate zone 5A under the 2021 International Energy Conservation Code (IECC).
Insulation minimums in Connecticut (zone 5A)
| Zone | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|
| 5A | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
Minimums from the 2021 IECC (Table R402.1.3). Many areas still enforce an older edition, so check with your local building department. See sources.
Which energy code Connecticut uses
Connecticut enforces the 2021 IECC with amendments for homes (in effect since Oct 2022). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments. See every state's energy code.
What changed from the 2018 map
None of Connecticut's counties changed zone between the 2018 and 2021 maps.
Every county in Connecticut
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Fairfield County | 5A | 5A | Insulation → |
| Hartford County | 5A | 5A | Insulation → |
| Litchfield County | 5A | 5A | Insulation → |
| Middlesex County | 5A | 5A | Insulation → |
| New Haven County | 5A | 5A | Insulation → |
| New London County | 5A | 5A | Insulation → |
| Tolland County | 5A | 5A | Insulation → |
| Windham County | 5A | 5A | Insulation → |
Source: Pacific Northwest National Laboratory, Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates (2022).
Frequently asked questions
What climate zone is Connecticut?
Connecticut is IECC climate zone 5A under the 2021 code.
How much attic insulation do I need in Connecticut?
The 2021 IECC calls for R-60 in the attic everywhere in Connecticut.
What energy code does Connecticut use?
Connecticut enforces the 2021 IECC with amendments for homes (in effect since Oct 2022). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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