What climate zone am I in? Look it up by ZIP
By Insulation Report Editorial. Last reviewed August 2026. How we research this.
In brief
A climate zone is a number from 1 to 8. The 2021 International Energy Conservation Code gives one to every US county, and it sets the insulation targets for houses there. Zone 1 is the hottest. It covers the southern tips of Florida and Texas, plus Hawaii. Zone 8 is the coldest, up in inland Alaska.
Type a five-digit ZIP into the tool on this page and it gives you three things. Your zone and how wet the climate is. The lowest ceiling value the 2021 IECC sets for new work in that zone. And the ENERGY STAR recommendation.
For a bare attic that last one is R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. Targets are lower if you already have some inches down. What your state enforces is a different question. Most states are not on the 2021 IECC, and our energy code tracker covers that.
Look up your zone
Figure 1
The 2021 IECC climate zones, by county
Zone 1 is the hottest and zone 8 the coldest, and your zone sets the attic R-value worth aiming for. Zones follow county lines, not state lines. So find your county, not your state. Several states cover three zones.
- Zone 1 R-30
- Zone 2 R-49
- Zone 3 R-49
- Zone 4 R-60
- Zone 5 R-60
- Zone 6 R-60
- Zone 7 R-60
- Zone 8 R-60
One input. The ZIP is matched to its county in your browser, against a table already on this page; nothing you type here is sent or stored, and this is not a lead form.
Every zone at a glance
This lookup is the 2021 IECC climate zone map in a different shape. The printed map colors each county by zone. Typing your ZIP here returns the same county assignment, from the same data, without squinting at a small state on a national map. If your project needs the map itself, the code publishes it as Figure R301.1 in the residential chapter.
Two different numbers per zone, and they answer different questions. The 2021 IECC ceiling minimum is model code for new construction and permitted work. The ENERGY STAR figures are voluntary retrofit guidance for the attic you already have, with a lower add-on target when 3 to 4 inches is already down, because the first inches do the most work.
| Zone | 2021 IECC ceiling minimum (new work) | ENERGY STAR, uninsulated attic | ENERGY STAR, already has 3 to 4 in |
|---|---|---|---|
| Zone 1 | R-30 | R-30 | R-25 |
| Zone 2 | R-49 | R-49 | R-38 |
| Zone 3 | R-49 | R-49 | R-38 |
| Zone 4 | R-60 | R-60 | R-49 |
| Zone 5 | R-60 | R-60 | R-49 |
| Zone 6 | R-60 | R-60 | R-49 |
| Zone 7 | R-60 | R-60 | R-49 |
| Zone 8 | R-60 | R-60 | R-49 |
Where the 2021 IECC asks for R-60 in the ceiling, R-49 is enough on one condition. The insulation has to run all the way out over the top of the outside wall at its full depth, with nothing squashing it. That normally takes a raised-heel truss, which lifts the roof to make room.
What the zone determines
Your zone sets the insulation target for every part of the house shell. For an attic, it picks your row in the table above. Two questions follow. How many inches is that in the material you are using? And what does putting it in cost? The attic insulation calculator answers both, off the same zone lookup. The full chart, across every part of the house and every material, is in the R-value guide.
What the zone does not determine
It does not tell you what your state enforces. The 2021 IECC is a model code. Each state chooses whether to adopt it. By our count from the ACEEE State Policy Database, reviewed November 2024, only 12 of the 51 places we track (the 50 states plus DC) are on the 2021 IECC or newer. Several have no statewide home code at all. So the code minimum in your result is what the 2021 edition says. It is not what a permit in your town will ask for. The energy code tracker lists what each state has adopted. Your local building department is the only authority on your address.
It also does not tell you whether any rule covers your project. Energy codes cover new building and work under a permit. Topping up the attic of a house you already own usually does not trigger the code at all. That is why the ENERGY STAR column is there. It is advice for exactly that case.
If your ZIP sits on a boundary
ZIP areas follow mail routes. Climate zones follow county lines. So about 3 percent of ZIPs sit across a zone line. When yours does, the result says so. The data holds only the zone of the county with the most land in that ZIP, so the tool cannot show you the other one. But the stakes are small. One zone step moves the attic target by at most one row of the table above. If you see the flag, check the zone for your own county with your local building department before you plan around it.
Where the zone data comes from
The lookup ties together two federal files. One is the county climate zone data from the Pacific Northwest National Laboratory and the Department of Energy, which carries the 2021 IECC zones. The other is the US Census Bureau 2020 ZCTA to county file, which lays ZIP areas over counties. The moisture letters follow the ASHRAE groups: A moist, B dry, C marine. Puerto Rico is missing because PNNL publishes no IECC zone for it, and the tool says so instead of guessing.
You may not need this page
Already know your zone, from a permit, an energy audit or a quote? Then there is nothing here for you past the table. And knowing your zone does not mean you need more insulation. The zone gives you a target. Whether your attic falls short of it is something you measure, not something you look up. We do not sell insulation and we do not install it, so nothing here needs you to buy anything. Measure what is up there first, with the depth checker. An attic already close to target usually gains more from air sealing than from more depth.
Short of your zone's target?
If the lookup and a depth measurement say your attic is well below the recommendation and you would rather not do the work yourself, tell us the job and your ZIP. We pass it to a licensed contractor who works in your area.
A marketing service, not a licensed contractor. Insulation work is performed by independent licensed local contractors.
- What does it cost?
- A 1,200 square foot attic blown to R-49 runs about $2,600 to $3,200 installed, from this site's own cost model dated August 2026. Two of its parts are estimates, so read it as a range and not a quote. See the full working and the price by attic size.
- What happens next?
- Your request goes to a licensed insulation contractor near you, usually within about an hour during the day.
Related
Common questions
What climate zone am I in?
Type your five-digit ZIP into the lookup on this page. US climate zones under the 2021 IECC run from 1 to 8. Zone 1 is the hottest: the southern tip of Florida, the southern tip of Texas, and Hawaii. Zones 2 and 3 cover most of the south and much of California. Zones 4 through 8 run from the mid-Atlantic and the Pacific Northwest up through Minnesota, Maine and inland Alaska. Zones are set by county. So the lookup finds your county from your ZIP using a Census Bureau file, then reads the zone from the Department of Energy and PNNL data.
Does a higher zone number mean a colder climate?
Yes. IECC zone 1 is the hottest and zone 8 the coldest. So the number goes up as it gets colder, and the recommended insulation goes up with it. For a bare attic that means R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. Watch out for USDA plant hardiness zones. Those run the other way, with the low numbers coldest. The two systems share nothing but the word zone.
Is my IECC climate zone the same as my USDA plant hardiness zone?
No. The Department of Agriculture draws the plant hardiness zones from winter low temperatures, to help you decide what to plant. Those number the coldest places first. The IECC climate zone is drawn for building energy codes, from heating and cooling patterns across the whole year. It numbers the hottest places first, and it is the one that sets insulation targets. A seed packet and a bag of insulation answer different questions. Do not carry a number from one to the other.
What if my ZIP is on a zone boundary?
About 3 percent of ZIP areas sit across a zone line, because ZIPs follow mail routes, not county lines. For those, this lookup gives you the zone of whichever county holds the most land in that ZIP, and it flags the result. The data does not carry the other zone. Moving one zone usually shifts the attic target by one row of the table on this page. If you see the flag and you are close to a cutoff, check your county zone with your local building department before you buy material.
What does the letter after the zone number mean?
It tells you how wet the climate is. A is moist, B is dry, C is marine. Minneapolis is 6A, Albuquerque is 4B, Seattle is 4C. The number is what drives your insulation target. The letter matters mostly for walls, for controlling water vapor, and for how vents are detailed, because a moist climate and a marine one want different building. A few places carry a number with no letter, because the source data leaves it blank there.
Why does the lookup not work for my ZIP?
The data behind it covers the 50 states and the District of Columbia. The PNNL and Department of Energy files publish no IECC zone for Puerto Rico, so those ZIPs come back empty rather than guessed. About 7,000 ZIPs are PO boxes or single addresses with no area of their own. For those, the lookup uses nearby ZIPs that share the first three digits, and tells you the zone was worked out that way.