Maryland Climate Zones by County
Maryland's 24 counties span climate zones 4A to 5A under the 2021 International Energy Conservation Code (IECC). Zone 4A is the most common, with 22 of the 24. For reference, Baltimore and Annapolis are in zone 4A and Cumberland is in 5A.
Insulation minimums for each zone in Maryland
| Zone | Counties | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 4A | 22 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 |
| 5A | 2 | 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 Maryland uses
Maryland enforces the 2021 IECC with amendments for homes (in effect since May 2023). 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
In the 2021 map, one moved colder: Allegany County (4 → 5). If your town still enforces the 2018 or 2015 code, the older zone applies to permits.
Every county in Maryland
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Allegany County | 5A | 4A changed | Insulation → |
| Anne Arundel County | 4A | 4A | Insulation → |
| Baltimore County | 4A | 4A | Insulation → |
| Baltimore (independent city) | 4A | 4A | Insulation → |
| Calvert County | 4A | 4A | Insulation → |
| Caroline County | 4A | 4A | Insulation → |
| Carroll County | 4A | 4A | Insulation → |
| Cecil County | 4A | 4A | Insulation → |
| Charles County | 4A | 4A | Insulation → |
| Dorchester County | 4A | 4A | Insulation → |
| Frederick County | 4A | 4A | Insulation → |
| Garrett County | 5A | 5A | Insulation → |
| Harford County | 4A | 4A | Insulation → |
| Howard County | 4A | 4A | Insulation → |
| Kent County | 4A | 4A | Insulation → |
| Montgomery County | 4A | 4A | Insulation → |
| Prince George's County | 4A | 4A | Insulation → |
| Queen Anne's County | 4A | 4A | Insulation → |
| Somerset County | 4A | 4A | Insulation → |
| St. Mary's County | 4A | 4A | Insulation → |
| Talbot County | 4A | 4A | Insulation → |
| Washington County | 4A | 4A | Insulation → |
| Wicomico County | 4A | 4A | Insulation → |
| Worcester 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 Maryland?
Maryland spans IECC climate zones 4A to 5A; zone 4A is the most common. Find your county in the table above, or search by ZIP code.
How much attic insulation do I need in Maryland?
The 2021 IECC calls for R-60 in the attic everywhere in Maryland.
What energy code does Maryland use?
Maryland enforces the 2021 IECC with amendments for homes (in effect since May 2023). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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