R-Value Calculator

Find the recommended insulation R-values for your location based on IECC climate zones and Energy Star guidelines.

Find Your R-Value Requirements

Enter your ZIP code to find the IECC-recommended insulation R-values for your climate zone.

Option 1: Enter ZIP Code

Option 2: Select Climate Zone Manually

Zone 1 = Hottest (Florida, Hawaii) | Zone 8 = Coldest (Alaska)

2021 IECC Requirements for All 8 Climate Zones

Complete reference table of minimum R-value requirements per the 2021 IECC (Table R402.1.3), broken down by zone and building assembly. Use this if you already know your zone or want to compare requirements across zones.

Zone 1 (Very Hot-Humid)

cooling

Southern Florida, Hawaii, Puerto Rico, US Virgin Islands

Ceiling/Attic	R-30
Wood Frame Wall	R-13
Floor	R-13
Basement Wall	NR
Crawl Space Wall	NR
Slab Edge	NR

HDD: 0–2,000 · CDD: 3,500–7,000

Zone 2 (Hot-Humid / Hot-Dry)

cooling

Southern Texas, Southern Louisiana, Southern Georgia, Southern Arizona

Ceiling/Attic	R-49
Wood Frame Wall	R-13
Floor	R-13
Basement Wall	NR
Crawl Space Wall	NR
Slab Edge	NR

HDD: 2,000–3,000 · CDD: 2,500–5,000

Zone 3 (Warm-Humid / Warm-Dry / Warm-Marine)

mixed

Northern Texas, Tennessee, North Carolina, Northern Arizona, Coastal California

Ceiling/Attic	R-49
Wood Frame Wall	R-20 or R-13+5ci
Floor	R-19
Basement Wall	R-5ci or R-13
Crawl Space Wall	R-5ci or R-13
Slab Edge	NR

HDD: 3,000–4,000 · CDD: 1,500–3,000

Zone 4 (Mixed-Humid / Mixed-Dry / Mixed-Marine)

heating

Virginia, Kentucky, Southern Missouri, Central Oregon, Maryland

Ceiling/Attic	R-60
Wood Frame Wall	R-20 or R-13+5ci
Floor	R-19 (R-30 Marine)
Basement Wall	R-10ci or R-13
Crawl Space Wall	R-10ci or R-13
Slab Edge	R-10, 2ft

HDD: 4,000–5,500 · CDD: 800–2,000

Zone 5 (Cold-Humid / Cold-Dry)

heating

Pennsylvania, Ohio, Indiana, Iowa, Colorado, Southern New England

Ceiling/Attic	R-60
Wood Frame Wall	R-20+5ci or R-13+10ci
Floor	R-30
Basement Wall	R-15ci or R-19
Crawl Space Wall	R-15ci or R-19
Slab Edge	R-10, 2ft

HDD: 5,500–7,000 · CDD: 400–1,200

Zone 6 (Cold)

heating

Minnesota, Wisconsin, Michigan, Northern New England, Montana

Ceiling/Attic	R-60
Wood Frame Wall	R-20+5ci or R-13+10ci
Floor	R-30
Basement Wall	R-15ci or R-19
Crawl Space Wall	R-15ci or R-19
Slab Edge	R-10, 4ft

HDD: 7,000–9,000 · CDD: 200–700

Zone 7 (Very Cold)

heating

Northern Minnesota, Northern Maine, parts of Alaska

Ceiling/Attic	R-60
Wood Frame Wall	R-20+5ci or R-13+10ci
Floor	R-38
Basement Wall	R-15ci or R-19
Crawl Space Wall	R-15ci or R-19
Slab Edge	R-10, 4ft

HDD: 9,000–12,500 · CDD: 0–400

Zone 8 (Subarctic/Arctic)

heating

Interior Alaska

Ceiling/Attic	R-60
Wood Frame Wall	R-20+5ci or R-13+10ci
Floor	R-38
Basement Wall	R-15ci or R-19
Crawl Space Wall	R-15ci or R-19
Slab Edge	R-10, 4ft

HDD: 12,500–20,000 · CDD: 0–100

“ci” = continuous insulation (uninterrupted by framing). “NR” = Not Required by IECC. Source: 2021 IECC Table R402.1.3 (residential prescriptive R-values), last verified May 2026. Local codes may differ—always verify with your building department.

Find Your Climate Zone by State or City

Most US states span just one or two climate zones. Find your state or major city below, or use the calculator above for a precise lookup by ZIP code.

Climate Zones by State

Zone 1R-30 attic

Hawaii
Puerto Rico
U.S. Virgin Islands
Guam

Zone 2R-49 attic

Florida (peninsula)
Texas (south)
Louisiana (south)

Zone 3R-49 attic

Alabama
Arkansas
Arizona (Phoenix/Tucson)
California (south & central)
Georgia
Mississippi
Nevada (Las Vegas)
New Mexico (south)
North Carolina (east)
Oklahoma (east)
South Carolina
Tennessee (west)
Texas (north)

Zone 4R-60 attic

California (north)
Delaware
District of Columbia
Kansas
Kentucky
Maryland
Missouri
New Jersey
New Mexico (north)
New York (south)
North Carolina (west)
Ohio (south)
Oklahoma (west)
Oregon (Portland, Marine 4C)
Pennsylvania (south)
Tennessee (east)
Virginia
Washington (Puget Sound, Marine 4C)
West Virginia

Zone 5R-60 attic

Colorado
Connecticut
Idaho (south)
Illinois
Indiana
Iowa
Massachusetts
Michigan (south)
Nebraska
Nevada (Reno/north)
New York (north)
Ohio (north)
Pennsylvania (north)
Rhode Island
Utah
Washington (east)
Wyoming (south)

Zone 6R-60 attic

Idaho (north)
Maine
Michigan (north)
Minnesota (south)
Montana
New Hampshire
North Dakota (south)
South Dakota
Vermont
Wisconsin
Wyoming (north)

Zone 7R-60 attic

Alaska (interior south)
Minnesota (far north)
North Dakota (north)

Zone 8R-60 attic

Alaska (interior north)

Climate Zones for Major US Cities

City	State	Zone	Attic R-Value	Wall R-Value
Albuquerque	NM	4	R-60	R-20 or R-13+5ci
Anchorage	AK	7	R-60	R-20+5ci or R-13+10ci
Atlanta	GA	3	R-49	R-20 or R-13+5ci
Austin	TX	2	R-49	R-13
Baltimore	MD	4	R-60	R-20 or R-13+5ci
Bismarck	ND	6	R-60	R-20+5ci or R-13+10ci
Boise	ID	5	R-60	R-20+5ci or R-13+10ci
Boston	MA	5	R-60	R-20+5ci or R-13+10ci
Buffalo	NY	5	R-60	R-20+5ci or R-13+10ci
Charlotte	NC	3	R-49	R-20 or R-13+5ci
Chicago	IL	5	R-60	R-20+5ci or R-13+10ci
Cincinnati	OH	4	R-60	R-20 or R-13+5ci
Cleveland	OH	5	R-60	R-20+5ci or R-13+10ci
Columbus	OH	5	R-60	R-20+5ci or R-13+10ci
Dallas	TX	3	R-49	R-20 or R-13+5ci
Denver	CO	5	R-60	R-20+5ci or R-13+10ci
Detroit	MI	5	R-60	R-20+5ci or R-13+10ci
El Paso	TX	3	R-49	R-20 or R-13+5ci
Fargo	ND	7	R-60	R-20+5ci or R-13+10ci
Fresno	CA	3	R-49	R-20 or R-13+5ci
Honolulu	HI	1	R-30	R-13
Houston	TX	2	R-49	R-13
Indianapolis	IN	5	R-60	R-20+5ci or R-13+10ci
Jacksonville	FL	2	R-49	R-13
Kansas City	MO	4	R-60	R-20 or R-13+5ci
Las Vegas	NV	3	R-49	R-20 or R-13+5ci
Los Angeles	CA	3	R-49	R-20 or R-13+5ci
Louisville	KY	4	R-60	R-20 or R-13+5ci
Memphis	TN	3	R-49	R-20 or R-13+5ci
Miami	FL	1	R-30	R-13
Milwaukee	WI	6	R-60	R-20+5ci or R-13+10ci
Minneapolis	MN	6	R-60	R-20+5ci or R-13+10ci
Nashville	TN	4	R-60	R-20 or R-13+5ci
New Orleans	LA	2	R-49	R-13
New York	NY	4	R-60	R-20 or R-13+5ci
Oklahoma City	OK	3	R-49	R-20 or R-13+5ci
Omaha	NE	5	R-60	R-20+5ci or R-13+10ci
Orlando	FL	2	R-49	R-13
Philadelphia	PA	4	R-60	R-20 or R-13+5ci
Phoenix	AZ	2	R-49	R-13
Pittsburgh	PA	5	R-60	R-20+5ci or R-13+10ci
Portland	OR	4	R-60	R-20 or R-13+5ci
Raleigh	NC	4	R-60	R-20 or R-13+5ci
Reno	NV	5	R-60	R-20+5ci or R-13+10ci
Sacramento	CA	3	R-49	R-20 or R-13+5ci
Salt Lake City	UT	5	R-60	R-20+5ci or R-13+10ci
San Antonio	TX	2	R-49	R-13
San Diego	CA	3	R-49	R-20 or R-13+5ci
San Francisco	CA	3	R-49	R-20 or R-13+5ci
Seattle	WA	4	R-60	R-20 or R-13+5ci
St. Louis	MO	4	R-60	R-20 or R-13+5ci
Tampa	FL	2	R-49	R-13
Tucson	AZ	2	R-49	R-13
Washington	DC	4	R-60	R-20 or R-13+5ci

Cities near zone boundaries (e.g., Raleigh NC, Reno NV, Boise ID) may fall into either of two zones depending on exact location and elevation. Use the calculator above to verify by ZIP code. Marine subzones (4C, 3C) apply to coastal Pacific Northwest and northern California; they share R-value requirements with their primary zone but have stricter vapor-control rules.

Understanding R-Value Requirements

What is R-Value?

R-value measures insulation's resistance to heat flow. The higher the R-value, the better the insulation performs. Different areas of your home need different R-values based on your climate zone and how heat moves through the building envelope.

About IECC Climate Zones

The International Energy Conservation Code (IECC) divides the United States into 8 climate zones, from Zone 1 (very hot/humid) to Zone 8 (subarctic). Each zone has specific minimum R-value requirements for different parts of a building.

Important Note

The R-values shown are 2021 IECC minimums. Your local building codes may require higher values. Always check with your local building department before starting an insulation project.

Code Minimum vs. Recommended

Code minimums are the legal requirements for new construction. However, Energy Star and building science experts often recommend exceeding these minimums for better comfort, lower energy bills, and future-proofing your home. The calculator shows both to help you make an informed decision.

Understanding "ci" Notation

When you see "ci" (continuous insulation) in the requirements, it means insulation installed on the exterior of the framing without thermal bridging through studs. For example, "R-13+5ci" means R-13 in the wall cavity plus R-5 continuous insulation on the outside.

Related Resources

R-Value Chart

Complete reference of R-values for all insulation types.

Climate Zone Map

Interactive map of IECC climate zones.

Cost Calculator

Estimate material and installation costs.

What is R-Value?

Learn how R-value works and why it matters.

Thickness Calculator

Find out how thick your insulation needs to be.

Insulation Quiz

Get personalized insulation recommendations.

Frequently Asked Questions

Why does my attic need higher R-values than my walls?

Heat rises, so the attic is where most heat escapes in winter. Additionally, there's typically more space in an attic to add insulation, and it's more cost-effective to add thickness there than in walls where space is limited.

What if my ZIP code shows a different zone than I expected?

Climate zones can vary within counties, especially near zone boundaries or in mountainous areas. If you're unsure, check with your local building department or use the manual zone selection based on the official IECC climate zone map.

Do these R-values apply to existing homes?

The IECC requirements technically apply to new construction. However, when retrofitting an existing home, these values serve as excellent targets. Your local utility may have specific rebate programs that reference these or similar R-value targets.

What does "NR" (Not Required) mean?

NR means the code doesn't require insulation in that location for your climate zone. However, you may still benefit from insulation there for comfort or energy savings. For example, Zone 1 doesn't require basement wall insulation by code, but adding some can still improve comfort.