Delaware Climate Zones by County
All three of Delaware's counties are in climate zone 4A under the 2021 International Energy Conservation Code (IECC).
Insulation minimums in Delaware (zone 4A)
| Zone | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|
| 4A | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 |
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 Delaware uses
Delaware enforces the 2024 IECC for homes (in effect since Apr 2026). 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 Delaware's counties changed zone between the 2018 and 2021 maps.
Every county in Delaware
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Kent County | 4A | 4A | Insulation → |
| New Castle County | 4A | 4A | Insulation → |
| Sussex County | 4A | 4A | 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 Delaware?
Delaware is IECC climate zone 4A under the 2021 code.
How much attic insulation do I need in Delaware?
The 2021 IECC calls for R-60 in the attic everywhere in Delaware.
What energy code does Delaware use?
Delaware enforces the 2024 IECC for homes (in effect since Apr 2026). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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