Massachusetts Climate Zones by County
All 14 of Massachusetts's counties are in climate zone 5A under the 2021 International Energy Conservation Code (IECC).
Insulation minimums in Massachusetts (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 Massachusetts uses
Massachusetts enforces the 2021 IECC with amendments for homes (in effect since Oct 2024). 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 Massachusetts's counties changed zone between the 2018 and 2021 maps.
Every county in Massachusetts
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Barnstable County | 5A | 5A | Insulation → |
| Berkshire County | 5A | 5A | Insulation → |
| Bristol County | 5A | 5A | Insulation → |
| Dukes County | 5A | 5A | Insulation → |
| Essex County | 5A | 5A | Insulation → |
| Franklin County | 5A | 5A | Insulation → |
| Hampden County | 5A | 5A | Insulation → |
| Hampshire County | 5A | 5A | Insulation → |
| Middlesex County | 5A | 5A | Insulation → |
| Nantucket County | 5A | 5A | Insulation → |
| Norfolk County | 5A | 5A | Insulation → |
| Plymouth County | 5A | 5A | Insulation → |
| Suffolk County | 5A | 5A | Insulation → |
| Worcester 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 Massachusetts?
Massachusetts is IECC climate zone 5A under the 2021 code.
How much attic insulation do I need in Massachusetts?
The 2021 IECC calls for R-60 in the attic everywhere in Massachusetts.
What energy code does Massachusetts use?
Massachusetts enforces the 2021 IECC with amendments for homes (in effect since Oct 2024). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
More for Massachusetts: Last frost dates in Massachusetts · Massachusetts planting zones · Frost line depth by state