New Hampshire Climate Zones by County
New Hampshire's 10 counties span climate zones 5A to 6A under the 2021 International Energy Conservation Code (IECC). Zone 6A is the most common, with 5 of the 10. For reference, Manchester, Portsmouth and Concord are in zone 5A.
Insulation minimums for each zone in New Hampshire
| Zone | Counties | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 5A | 5 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 6A | 5 | 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 New Hampshire uses
New Hampshire enforces the 2018 IECC for homes (in effect since Jul 2022). 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
One county moved one zone warmer in the 2021 map: Merrimack County (6 → 5). If your town still enforces the 2018 or 2015 code, the older zone applies to permits.
Every county in New Hampshire
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Belknap County | 6A | 6A | Insulation → |
| Carroll County | 6A | 6A | Insulation → |
| Cheshire County | 5A | 5A | Insulation → |
| Coos County | 6A | 6A | Insulation → |
| Grafton County | 6A | 6A | Insulation → |
| Hillsborough County | 5A | 5A | Insulation → |
| Merrimack County | 5A | 6A changed | Insulation → |
| Rockingham County | 5A | 5A | Insulation → |
| Strafford County | 5A | 5A | Insulation → |
| Sullivan County | 6A | 6A | 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 New Hampshire?
New Hampshire spans IECC climate zones 5A to 6A; zone 6A is the most common. Find your county in the table above, or search by ZIP code.
How much attic insulation do I need in New Hampshire?
The 2021 IECC calls for R-60 in the attic everywhere in New Hampshire.
What energy code does New Hampshire use?
New Hampshire enforces the 2018 IECC for homes (in effect since Jul 2022). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
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