R-value insulation chart: what R-value do I need by climate zone?

"What R-value insulation do I need?" has one honest answer: it depends on three things — your climate zone, the part of the house you are insulating, and which edition of the energy code your town enforces. Once you know those three, the number comes straight out of a table. Here is that table, zone by zone, with what it means in inches for attics, walls and floors.

R-value insulation chart by climate zone

Quick answer: under the 2021 IECC, attics need R-30 to R-60 and wood-frame walls R-13 to R-21, rising as the climate gets colder. Find your zone in Step 1, then read across:

These are code minimums for new work from Table R402.1.3; the steps below explain the zones, the older code editions many towns still use, and how many inches each R-value takes.

Step 1 — Find your climate zone

The International Energy Conservation Code (IECC) splits the US into climate zones from 1 (hottest) to 8 (coldest). As a rough guide:

• Zone 1: South Florida, Hawaii, Puerto Rico
• Zone 2: Gulf Coast, South Texas, Central Florida
• Zone 3: North Texas, Georgia, Southern California
• Zone 4: Virginia, Kansas, the Oregon coast
• Zone 5: Illinois, Massachusetts, Colorado
• Zone 6: Minnesota, Vermont, Montana
• Zone 7: Northern Minnesota, Northern Maine, the Alaska panhandle
• Zone 8: Northern Alaska

Zones follow county lines, not state lines, so a big state can span two or three. Your county's zone is listed in the IECC (Table R301.1) and on the DOE Building America IECC climate zone map, and your building department can confirm it.

Step 2 — Look up the R-value for each part of the house

These are the code-minimum R-values from the 2021 IECC (Table R402.1.3), the edition most recent state updates are based on:

• Attic / ceiling: R-30 in zone 1, R-49 in zones 2–3, R-60 in zones 4–8
• Wood-frame wall cavity: R-13 in zones 1–2, R-20 in zones 3–6, R-21 in zones 7–8. In the colder zones the code pairs the cavity with continuous insulation on the outside (for example R-20 + R-5), and it also allows smaller cavity + board combinations such as R-13 + R-5 — check the table for your zone.
• Floor over an unheated space: R-13 in zones 1–2, R-19 in zones 3–4, R-30 in zones 5–6, R-38 in zones 7–8
• Crawl space wall (continuous): none in zones 1–2, R-5 in zone 3, R-10 in zone 4, R-15 in zones 5–8
• Basement wall (continuous): none in zones 1–2, R-5 in zone 3, R-10 in zone 4, R-15 in zones 5–8

A vaulted or cathedral ceiling is a ceiling, so it follows the attic row. A rim joist is part of the wall, so it follows the wall row.

Step 3 — Check which code year applies

Not every state has adopted the 2021 edition, and the attic number is where the editions differ most:

• 2009 IECC: R-30 in zones 1–3, R-38 in zones 4–5, R-49 in zones 6–8
• 2012, 2015 and 2018 IECC: R-30 in zone 1, R-38 in zones 2–3, R-49 in zones 4–8
• 2021 IECC: R-30 in zone 1, R-49 in zones 2–3, R-60 in zones 4–8

So an attic in Illinois (zone 5) is R-38 under the 2009 code, R-49 under 2012–2018 and R-60 under 2021. Code minimums are the floor for new work; when you are paying for labor and a blowing machine anyway, going to the newer, higher figure is rarely wasted. Your local building department has the final word, including any state amendments.

Step 4 — Turn the R-value into inches

depth (inches) = target R ÷ R per inch of the material

Using typical R-per-inch figures — blown cellulose R-3.5, blown fiberglass R-2.5, fiberglass batts about R-3.14, mineral wool batts about R-4.2, closed-cell spray foam about R-6.5 — the attic targets work out to:

• R-30: 8.6 in of cellulose or 12 in of blown fiberglass
• R-49: 14 in of cellulose or 19.6 in of blown fiberglass
• R-60: 17.1 in of cellulose or 24 in of blown fiberglass

Those are settled depths. Cellulose settles, so it is blown about 11% deeper — roughly 19 in on the day for R-60. Loose fiberglass does not settle appreciably.

When the cavity is too shallow

Walls and vaulted ceilings have a hard limit: the depth of the framing. A 2 × 6 wall is 5.5 in deep. Standard fiberglass batts at about R-3.14 per inch top out near R-17 there — short of an R-20 target. To reach R-20 in 5.5 in you need at least R-3.64 per inch: a high-density R-21 batt, a mineral wool batt (R-23 products are made for 2 × 6), or dense-packed cellulose at about R-3.7 per inch.

A 2 × 4 wall (3.5 in) cannot reach R-20 with any common cavity fill except spray foam, which is why the code offers cavity + continuous options: R-13 batts plus R-5 rigid board over the studs.

Already have some insulation?

Measure what is there, multiply by its R per inch, and add only the difference. An attic with about 6 in of old fiberglass batts has roughly R-19; bringing it to R-49 needs R-30 more — about 8.6 in of cellulose on top. For the bag math, see our guide to how much insulation you need.

Our app: Smart Insulation Calculator

Smart Insulation Calculator is a free Android app that keeps this whole table on the phone, offline. Pick your zone and code year (IECC 2009 through 2021) and every tool starts from the code-minimum R-value for that assembly — attic, wall, floor, crawl space or basement wall, cathedral ceiling or rim joist. It then shows the chain on screen: target R, material, depth, area, and the bags, batts, foam kits or boards to buy. If the framing is too shallow for the target, it says so and names a material that fits. Every R-value in this article comes from the app's own tables, and every default is editable.

It is on Google Play for Android only, and the calculators also run in any browser at smartinsulationcalculator.com. Tiling the bathroom next? See how much grout you need.

Once you know the R-value, turn it into bags, rolls or board feet with how much insulation do I need.