Pennsylvania Climate Zones by County
Pennsylvania's 67 counties span climate zones 4A to 5A under the 2021 International Energy Conservation Code (IECC). Zone 5A is the most common, with 53 of the 67. For reference, Philadelphia is in zone 4A and Pittsburgh and Erie are in 5A.
Insulation minimums for each zone in Pennsylvania
| Zone | Counties | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 4A | 14 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 |
| 5A | 53 | 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 Pennsylvania uses
Pennsylvania enforces the 2021 IECC with amendments for homes (in effect since Jan 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
16 counties moved one zone warmer in the 2021 map: Adams County (5 → 4), Berks County (5 → 4), Cameron County (6 → 5), Clearfield County (6 → 5), Cumberland County (5 → 4), Dauphin County (5 → 4), Elk County (6 → 5), Franklin County (5 → 4), Lancaster County (5 → 4), Lebanon County (5 → 4), McKean County (6 → 5), Perry County (5 → 4), and 4 more marked in the table below. If your town still enforces the 2018 or 2015 code, the older zone applies to permits.
Every county in Pennsylvania
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Adams County | 4A | 5A changed | Insulation → |
| Allegheny County | 5A | 5A | Insulation → |
| Armstrong County | 5A | 5A | Insulation → |
| Beaver County | 5A | 5A | Insulation → |
| Bedford County | 5A | 5A | Insulation → |
| Berks County | 4A | 5A changed | Insulation → |
| Blair County | 5A | 5A | Insulation → |
| Bradford County | 5A | 5A | Insulation → |
| Bucks County | 4A | 4A | Insulation → |
| Butler County | 5A | 5A | Insulation → |
| Cambria County | 5A | 5A | Insulation → |
| Cameron County | 5A | 6A changed | Insulation → |
| Carbon County | 5A | 5A | Insulation → |
| Centre County | 5A | 5A | Insulation → |
| Chester County | 4A | 4A | Insulation → |
| Clarion County | 5A | 5A | Insulation → |
| Clearfield County | 5A | 6A changed | Insulation → |
| Clinton County | 5A | 5A | Insulation → |
| Columbia County | 5A | 5A | Insulation → |
| Crawford County | 5A | 5A | Insulation → |
| Cumberland County | 4A | 5A changed | Insulation → |
| Dauphin County | 4A | 5A changed | Insulation → |
| Delaware County | 4A | 4A | Insulation → |
| Elk County | 5A | 6A changed | Insulation → |
| Erie County | 5A | 5A | Insulation → |
| Fayette County | 5A | 5A | Insulation → |
| Forest County | 5A | 5A | Insulation → |
| Franklin County | 4A | 5A changed | Insulation → |
| Fulton County | 5A | 5A | Insulation → |
| Greene County | 5A | 5A | Insulation → |
| Huntingdon County | 5A | 5A | Insulation → |
| Indiana County | 5A | 5A | Insulation → |
| Jefferson County | 5A | 5A | Insulation → |
| Juniata County | 5A | 5A | Insulation → |
| Lackawanna County | 5A | 5A | Insulation → |
| Lancaster County | 4A | 5A changed | Insulation → |
| Lawrence County | 5A | 5A | Insulation → |
| Lebanon County | 4A | 5A changed | Insulation → |
| Lehigh County | 5A | 5A | Insulation → |
| Luzerne County | 5A | 5A | Insulation → |
| Lycoming County | 5A | 5A | Insulation → |
| McKean County | 5A | 6A changed | Insulation → |
| Mercer County | 5A | 5A | Insulation → |
| Mifflin County | 5A | 5A | Insulation → |
| Monroe County | 5A | 5A | Insulation → |
| Montgomery County | 4A | 4A | Insulation → |
| Montour County | 5A | 5A | Insulation → |
| Northampton County | 5A | 5A | Insulation → |
| Northumberland County | 5A | 5A | Insulation → |
| Perry County | 4A | 5A changed | Insulation → |
| Philadelphia County | 4A | 4A | Insulation → |
| Pike County | 5A | 5A | Insulation → |
| Potter County | 5A | 6A changed | Insulation → |
| Schuylkill County | 5A | 5A | Insulation → |
| Snyder County | 5A | 5A | Insulation → |
| Somerset County | 5A | 5A | Insulation → |
| Sullivan County | 5A | 5A | Insulation → |
| Susquehanna County | 5A | 6A changed | Insulation → |
| Tioga County | 5A | 6A changed | Insulation → |
| Union County | 5A | 5A | Insulation → |
| Venango County | 5A | 5A | Insulation → |
| Warren County | 5A | 5A | Insulation → |
| Washington County | 5A | 5A | Insulation → |
| Wayne County | 5A | 6A changed | Insulation → |
| Westmoreland County | 5A | 5A | Insulation → |
| Wyoming County | 5A | 5A | Insulation → |
| York 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 Pennsylvania?
Pennsylvania spans IECC climate zones 4A to 5A; zone 5A is the most common. Find your county in the table above, or search by ZIP code.
How much attic insulation do I need in Pennsylvania?
The 2021 IECC calls for R-60 in the attic everywhere in Pennsylvania.
What energy code does Pennsylvania use?
Pennsylvania enforces the 2021 IECC with amendments for homes (in effect since Jan 2026). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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