Washington, DC Climate Zone
The District of Columbia is in climate zone 4A under the 2021 International Energy Conservation Code (IECC).
Insulation minimums in DC (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 DC uses
DC enforces the 2015 IECC with amendments for homes (in effect since May 2020). 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
DC was zone 4A in both the 2018 and 2021 maps.
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 Washington, DC?
Washington, DC is IECC climate zone 4A under the 2021 code.
How much attic insulation do I need in Washington, DC?
The 2021 IECC calls for R-60 in the attic everywhere in Washington, DC.
What energy code does Washington, DC use?
DC enforces the 2015 IECC with amendments for homes (in effect since May 2020). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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