Skip to content
ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Insulation R-Value Chart:
Every Material, Per Inch
& By Climate Zone

R-value per inch for every common insulation, how deep you need to go for R-38 or R-60, and the 2021 IECC minimums for each climate zone, with two calculators.
Insulation Quotes

Not sure what R-value you have? We will measure it.

Tell us where the house is, which areas you want insulated (attic, walls, roof deck, crawl space), what is there now and roughly how many square feet. We will connect you with a certified applicator near you.

  • City or ZIP code
  • Areas to insulate
  • Existing insulation and depth
  • Approximate square footage
Rather talk now? Call (417) 831-5090
Step 1 of 3
R-60
Minimum attic (ceiling) insulation for new homes in climate zones 4 through 8
2021 IECC via PNNL
13.5 in
Blown fiberglass depth needed to reach R-38 in an open attic
Owens Corning AttiCat chart
10.5 in
Settled depth of blown cellulose for the same R-38
GreenFiber fact sheet
10%
Possible savings on annual energy bills from sealing and insulating
ENERGY STAR

This insulation R-value chart puts every common material on one page: R-value per inch, how much fits in a 2x4 wall, how deep you have to go to reach R-38 or R-60, and the minimum R-values the 2021 IECC sets for each climate zone. We manufacture spray foam, but most of the attics, walls and crawl spaces we look at need a mix of materials, so this guide compares all of them on the same terms. Use the two calculators to convert a target R-value into inches and to check whether the insulation already in your attic meets code for your zone.

Quick answer

Per inch, closed-cell spray foam (about R-6.5) and polyiso board (R-5.0 to R-5.6 for design) insulate best, followed by XPS (R-5), mineral wool and high-density batts (about R-4.3), EPS (R-3.6 to R-4.2), cellulose and open-cell foam (about R-3.6) and blown fiberglass (R-2.2 to R-2.8). For code, the 2021 IECC calls for R-30 attics in zone 1, R-49 in zones 2 and 3 and R-60 in zones 4 through 8. Per-inch numbers only matter when space is tight; in an open attic, cheap blown insulation piled deep usually wins on cost per R.

What's in this guide
  1. 1What R-value measures
  2. 2Insulation R-value chart by material
  3. 3R-value thickness calculator
  4. 4R-value requirements by climate zone
  5. 5Attic insulation code checker
  6. 6Which material belongs where
  7. 7Why installed R-value falls short
  8. 8FAQ
The basics

What an R-value actually measures

R-value is a material's resistance to conductive heat flow. The Department of Energy puts it simply: the higher the R-value, the better the insulation works. Three rules from DOE explain most of the confusion we hear on job sites:

  • R-values add up. Two layers of R-19 make R-38. Six inches of old cellulose plus a new layer of blown fiberglass is the sum of both.
  • Compressed insulation loses R-value. A batt stuffed into a cavity thinner than it was made for does not deliver the number on the bag.
  • Framing leaks heat. Studs, joists and plates conduct heat faster than the insulation between them. DOE calls this thermal bridging, and it is why a wall full of R-21 batts performs below R-21 as a whole.

The number on the label comes from a lab test. Under the FTC's R-value Rule (16 CFR Part 460), manufacturers test at a mean temperature of 75°F with a 50°F temperature difference, using standard ASTM methods. That makes products comparable, but real attics are hotter and colder than that. Building Science Corporation's testing of polyiso is the best-known example: its R-value drops as the outside temperature goes below freezing, so BSC recommends designing with R-5.6 per inch in warm climates and R-5.0 per inch in cold ones.

What you are owedThe same FTC rule requires installers to give you a receipt showing the coverage area, thickness and R-value installed. For loose-fill, the receipt also lists initial installed thickness, minimum settled thickness and the number of bags used. Ask for it, and count the empty bags if you can.
The chart

Insulation R-value chart by material

The table lists the published range for each material and the single value we use in the calculators below. Where a manufacturer chart exists, we used it: blown fiberglass from the Owens Corning AttiCat coverage chart (R-38 at 13.5 inches, so about R-2.8 per inch) and cellulose from the GreenFiber fact sheet (R-38 at 10.5 inches settled, about R-3.6). Click any column header to sort.

MaterialR per inch (range)Value usedR in a 2x4 cavity (3.5 in)Inches for R-38Inches for R-60Stops air?
Blown fiberglass (loose-fill)2.2–2.82.8R-9.813.621.4No
Blown rock wool (loose-fill)2.82.8R-9.813.621.4No
Fiberglass batt, standard3.1–3.73.4R-11.9 (R-13 batt)11.217.6No
Open-cell spray foam3.5–3.73.6R-12.610.616.7Yes, at full depth
Blown cellulose (settled)3.6–3.73.6R-12.610.616.7Slows it (dense-pack)
EPS foam board3.6–4.24.0R-14.09.515.0If seams taped
Mineral wool batt3.1–4.34.3R-158.814.0No
High-density fiberglass batt3.8–4.34.3R-158.814.0No
XPS foam boardabout 55.0R-17.57.612.0If seams taped
Polyiso foam board5.0–5.6 design5.6R-19.66.810.7If seams taped
Closed-cell spray foam6.2–7.06.5R-22.85.89.2Yes, at about 1 in
Radiant barrier foilNo rated R per inchn/an/an/an/aNo
Sources: DOE R-value list (via Oncor) for loose-fill, batt and spray foam ranges; Owens Corning AttiCat and GreenFiber coverage charts; DOE Types of Insulation (R-13 or R-15 batts fit 2x4 walls); Rmax (XPS about R-5, EPS R-3.6 to R-4.2); Building Science Corporation Info-502 (polyiso design values); ArmorThane closed-cell data. Values are at the FTC test condition of 75°F mean temperature. The R in a 2x4 column is cavity-only and ignores framing.

For spray foam specifically, including open-cell versus closed-cell and how many inches hit code, see our spray foam R-value guide. Two things jump out of this broader chart. First, the gap between the best and worst materials is more than 2 to 1 per inch, which is why spray foam and foam board dominate where depth is limited: 2x4 walls, cathedral ceilings, rim joists and metal buildings. Second, in an open attic, depth is cheap. Thirteen and a half inches of blown fiberglass reaches the same R-38 as about six inches of closed-cell foam, and on an attic floor there is usually room for both and more.

Radiant barrier foil is in the table because people ask about it constantly. It reflects radiant heat rather than resisting conduction, so it has no R-value per inch of its own; its effect depends on the air space next to it. We cover that in our radiant barrier guide.

Calculator

R-value thickness calculator

Enter the R-value you want and the depth you have. The tool divides the target by each material's per-inch value from the chart, shows how many inches each one needs, and highlights the materials that fit in your space.

Inches needed

How thick does it need to be?

Inches = target R ÷ R per inch. Uses the "value used" column above. Cavity-only, so framing losses are not included.

A preset chip overrides this box
2x4 = 3.5, 2x6 = 5.5, 2x8 = 7.25, 2x10 = 9.25
—
Materials that fit
—
Closed-cell foam needed
—
Blown fiberglass needed

Code minimums

R-value requirements by climate zone (2021 IECC)

The 2021 International Energy Conservation Code sets minimum insulation for new homes and additions in its prescriptive R-value table (R402.1.3). Your state or city may still enforce an older edition or its own amendments, so treat this as the national model and call your building department before you buy material. In wall entries, "13+5ci" means R-13 in the cavity plus R-5 of continuous insulation (usually foam board) over the studs.

Climate zoneExample citiesCeiling / atticWood-frame wallFloorBasement wallSlab edgeCrawl space wall
1MiamiR-3013 or 0+10ciR-13NoneNoneNone
2Houston, PhoenixR-4913 or 0+10ciR-13NoneNoneNone
3Atlanta, Dallas, Los AngelesR-4920 or 13+5ci or 0+15ciR-195ci or 13R-10, 2 ft5ci or 13
4 (except marine)St. Louis, Springfield MO, NashvilleR-6030 or 20+5ci or 13+10ci or 0+20ciR-1910ci or 13R-10, 4 ft10ci or 13
5 and marine 4Chicago, Denver, SeattleR-6030 or 20+5ci or 13+10ci or 0+20ciR-30*15ci or 19 or 13+5ciR-10, 4 ft15ci or 19 or 13+5ci
6Minneapolis, Burlington VTR-6030 or 20+5ci or 13+10ci or 0+20ciR-30*15ci or 19 or 13+5ciR-10, 4 ft15ci or 19 or 13+5ci
7 and 8Duluth, FairbanksR-6030 or 20+5ci or 13+10ci or 0+20ciR-38*15ci or 19 or 13+5ciR-10, 4 ft15ci or 19 or 13+5ci
Source: 2021 IECC Table R402.1.3 as compiled by PNNL's Building America Solution Center. *The code footnote lets you use insulation that fills the floor framing cavity instead, with R-19 minimum. Mass-wall values are omitted for space. Example cities are for orientation only; zones are assigned by county.

ENERGY STAR targets for existing homes

The IECC applies to new work. For a house that already exists, ENERGY STAR publishes retrofit targets for attics and floors. If your attic has no insulation, ENERGY STAR's target is R-30 in zone 1, R-49 in zones 2 and 3 and R-60 in zones 4 through 8. If you already have 3 to 4 inches, it recommends adding R-25 in zone 1, R-38 in zones 2 and 3 and R-49 in zones 4 through 8. Floor targets run from R-13 in zones 1 and 2 to R-38 in zones 7 and 8.

The DOE gives a simpler test: if the attic has less than the equivalent of R-30, which it describes as about 10 to 13 inches, you could probably benefit from adding more. Our attic insulation cost guide prices that top-up by material, and our guide to the cost to insulate a house covers walls, crawl spaces and basements too.

Calculator

Attic insulation code checker

Measure the depth of your existing attic insulation in a few spots (use the lowest typical reading, not the peak of a drift), pick your zone and material, and the tool estimates your current R-value, compares it with the 2021 IECC attic minimum, and works out how much blown fiberglass or cellulose you would add to close the gap.

Code gap

Does your attic meet code?

Current R = depth × R per inch. Bags are scaled from the AttiCat (19 bags per 1,000 sq ft at R-38) and GreenFiber (60.1 bags per 1,000 sq ft at R-38) coverage charts. Bag sizes differ by brand, so read the chart on the bag you buy.

Top up with
—
Estimated R today
—
2021 IECC attic minimum
—
Inches to add
—
Approx. bags

Choosing

Which material belongs where

The R-value chart tells you what each material can do per inch. Where it goes depends on space, air leakage, moisture and budget. This is how we would split a typical house.

Open attic floor

Blown cellulose or fiberglass

Depth is free here, so the lowest cost per R wins. Air seal the top plates, wiring holes and the hatch first, as DOE advises, then blow to R-49 or R-60. Spray foam on an attic floor rarely pays off.

Cathedral ceilings and roof decks

Closed-cell or open-cell spray foam

Rafter depth limits you, and the roof deck needs an air seal. Closed-cell gets about R-38 in under 6 inches. See our attic foam insulation page for vented versus unvented details.

2x4 and 2x6 walls

Batts, dense-pack or foam

Mineral wool or high-density batts give R-15 in a 2x4. Existing finished walls get dense-pack cellulose through drilled holes. Closed-cell foam reaches the highest cavity R and adds rigidity, at a higher price.

Rim joists and crawl space walls

Closed-cell foam or foam board

These are the leakiest, dampest spots in most houses. Closed-cell foam air seals and acts as a vapor retarder in one pass. Board works too if every edge is sealed. More in our closed-cell spray foam guide; for the water and heating lines that run through these spaces, see pipe insulation.

Real-world performance

Why installed R-value falls short of the chart

Every number in an insulation R-value chart is a best case. Here is where we see the gap open up when we inspect existing homes:

  1. Settling

    Loose-fill settles after it is blown. GreenFiber's chart shows R-38 cellulose going in at 11.7 inches and settling to 10.5, which is why the FTC rule requires bags to list both initial and minimum settled thickness. If an installer blows to the settled depth, you end up short.

  2. Compression

    A batt rated for 6.25 inches jammed into a 5.5-inch cavity, or flattened under attic storage, loses R-value. DOE is explicit that compressed insulation will not provide its full rated R-value.

  3. Framing and gaps

    Studs and joists are thermal bridges. Gaps around wiring, boxes and blocking let air move around the insulation. Continuous insulation over the framing, the "ci" in the code table, is how the IECC deals with it.

  4. Air movement

    Fibrous insulation slows heat but does not stop air. Wind washing at the eaves and warm air rising through top-plate gaps carry heat straight past it. That is why air sealing comes first on any attic job.

  5. Temperature

    Labels are tested at 75°F mean. Polyiso in particular loses R-value in the cold, which is why Building Science Corporation designs with R-5.0 per inch in cold climates instead of R-5.6.

Before you add anythingIf your attic has vermiculite, the gray-brown or silver-gold pebble-like fill, EPA says to assume it contains asbestos and leave it undisturbed. Do not blow new insulation over it or store boxes on it until a professional asbestos contractor has assessed it. Our attic insulation removal guide covers what comes next.
Spray foam where space is tight

Need R-38 in a 2x8 roof? Closed-cell gets there.

Our certified applicators spray ArmorFoam closed-cell and open-cell foam in roof decks, walls, rim joists and crawl spaces, and they will tell you when blown insulation is the better buy.

Get a free quoteFind an applicator

Contractors: become an applicator →

FAQ

Insulation R-value questions

Which insulation has the highest R-value per inch?

Among common building insulation, closed-cell spray foam is highest at roughly R-6.2 to R-7.0 per inch, followed by polyiso board (designed at R-5.0 to R-5.6) and XPS board (about R-5). Blown fiberglass is lowest at about R-2.2 to R-2.8 per inch.

What R-value do I need in my attic?

The 2021 IECC requires R-30 in climate zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8 for new construction. ENERGY STAR uses the same figures as targets for uninsulated attics in existing homes.

How many inches of insulation is R-38?

It depends on the material. Owens Corning's AttiCat chart lists 13.5 inches of blown fiberglass for R-38, GreenFiber lists 10.5 inches of settled cellulose, and closed-cell spray foam at about R-6.5 per inch needs just under 6 inches.

How many inches of insulation is R-60?

Owens Corning's AttiCat chart lists 20.5 inches of blown fiberglass for R-60, and GreenFiber lists 16.5 inches of settled cellulose. Plan for enough baffles at the eaves to keep that depth from blocking soffit vents.

Can I add R-values of different insulation layers?

Yes. DOE says to add the R-values of the individual layers. Six inches of existing cellulose at about R-3.6 per inch is roughly R-22, and adding R-38 of blown fiberglass on top brings the attic to about R-60.

Does a higher R-value always save more money?

No. Each added inch saves less than the one before it, and air leaks can cancel much of the benefit. ENERGY STAR estimates that sealing and insulating together can save up to 10% on annual energy bills. Seal first, then insulate to the level recommended for your zone.

Is the 2021 IECC the code in my area?

Not necessarily. States and cities adopt energy codes on their own schedule and often amend them. Use the 2021 IECC table as a benchmark and confirm the adopted edition with your local building department before you plan a project.

Do radiant barriers have an R-value?

Not in the usual sense. A radiant barrier reflects radiant heat and its effect depends on an air space beside it. ASTM C1313 defines radiant barrier sheet materials by a surface emittance of 0.1 or less, not by R-value.

AT
Written by the ArmorThane technical team. We have manufactured spray foam, polyurea and protective coatings since 1989 and train the applicators who install them. Code tables checked against the 2021 IECC. Updated October 2026.

Sources

  1. PNNL Building America Solution Center, 2009–2021 IECC and IRC minimum insulation requirements: basc.pnnl.gov
  2. ENERGY STAR, recommended home insulation R-values: energystar.gov
  3. ENERGY STAR, seal and insulate: energystar.gov/saveathome/seal_insulate
  4. U.S. Department of Energy, Insulation: energy.gov/energysaver/insulation
  5. U.S. Department of Energy, Types of Insulation: energy.gov/energysaver/types-insulation
  6. U.S. Department of Energy, Where to Insulate in a Home: energy.gov/energysaver/where-insulate-home
  7. Insulation R-values per inch, DOE data compiled by Oncor: oncor.com
  8. Federal Trade Commission R-value Rule, 16 CFR Part 460: ecfr.gov
  9. Owens Corning, AttiCat blown-in insulation fact sheet: owenscorning.com (fact sheet)
  10. GreenFiber, loose-fill cellulose fact sheet: greenfiber fact sheet
  11. Building Science Corporation, Info-502, temperature dependence of polyiso R-values: buildingscience.com
  12. Rmax, ASTM C578 explained (EPS and XPS R-values): rmax.com
  13. ROCKWOOL Comfortbatt product data: rockwool.com
  14. ASTM C1313, standard specification for sheet radiant barriers: astm.org
  15. EPA, asbestos-contaminated vermiculite insulation: epa.gov

latest news & bLOGS

Learn more

Hit your R-value target the first time.

Homeowners get a certified ArmorThane applicator who installs closed-cell and open-cell foam where depth is tight and tells you when blown insulation is the smarter buy. Contractors can add spray foam with no franchise fee and no royalties.

Find an applicator →Become an applicator
United States 417-831-5090 · Canada 780-444-6200

CONTACT US

REQUEST A QUOTE OR

BECOME AN APPLICATOR

ArmorThane has built a strong reputation over the past 30 years for producing high-quality, durable protective coatings.

group 115 660555abebfe4
Phone Number

Tel: 417.831.5090

group 115 1 660556c21395c
Email Us

moreinfo@armorthane.com

Step 1 of 3

We want to help you find the best ArmorThane applicator for your protective coating project. Please either fill out the request form below or call us toll free at 417-831-5090, any time Monday-Friday, 8:00 a.m. to 5:00 p.m. Central Standard Time.

RV Find An Applicator

Step 1 of 3

Connect with an authorized ArmorThane professional to get a long-lasting, seamless protective coating for your RV. Submit the form below or call us directly at 417-831-5090 (Monday–Friday, 8:00 AM – 5:00 PM CST).

Facebook Twitter Youtube

Find An Applicator

Applicator Login

Armorthane Logo Outlined
CALL NOW
BECOME APPLICATOR
FIND APPLICATOR

Protective Coating Applications

Products

Applicator Opportunities

Knowledge Center

Galleries