How thick does spray foam need to be to meet building code?

It depends on your climate zone and application. In IECC climate zone 5, for example, an attic requires R-49 minimum. ThermoSeal HFO at R-7.4/inch would need approximately 6.7 inches to meet that requirement. Use the calculator above to find the exact thickness needed for your location and application.

Spray Foam R-Value Calculator

Q: Does spray foam R-value degrade over time?

Open cell spray foam (ThermoSeal 500 and 800) is water blown and does not experience R-value degradation. Closed cell spray foam (ThermoSeal HFO and 5G) uses HFO blowing agents; the long-term R-values shown are stabilized values per LTTR (Long-Term Thermal Resistance) testing, not initial values.

R-Value Calculator

1. Select Product

ThermoSeal 500 Open Cell · 0.5 lb/ft³ R-4.1 / inch

ThermoSeal 800 Open Cell · 0.75 lb/ft³ R-4.5 / inch

ThermoSeal HFO Closed Cell · 2.0 lb/ft³ R-7.4 / inch

ThermoSeal 5G Closed Cell · Commercial R-7.3 / inch

2. Application & Climate Zone

3. Foam Thickness

3.5 inches

½"3"6"9"12"

Total R-Value Achieved

R-14.4

IECC 2021 Code Minimum R-49

R-Value Remaining —

Meets code minimum

* R-values per ASTM C 518. IECC 2021 requirements shown are for insulation-only R-value; actual code compliance depends on wall assembly type, local amendments, and installation method. Always verify with your local building department.

Product R-Values (ASTM C 518)

ThermoSeal 500

Open Cell · Water Blown

R-4.1/in

ThermoSeal 800

Open Cell · Water Blown

R-4.5/in

ThermoSeal HFO

Closed Cell · HFO Blown

R-7.4/in

ThermoSeal 5G

Closed Cell · Commercial

R-7.3/in

IECC 2021: Code Minimums by Zone

Zone	Attic	Wall	Floor
Zone 1	R-30	R-13	R-13
Zone 2	R-38	R-20	R-19
Zone 3	R-38	R-20	R-19
Zone 4	R-49	R-20	R-19
Zone 5	R-49	R-20	R-30
Zone 6	R-49	R-20	R-30
Zone 7	R-49	R-21	R-38
Zone 8	R-49	R-21	R-38

Important Notes

Open cell foam (500, 800) requires a vapor retarder in Climate Zones 5–8 when used in walls.

Closed cell foam (HFO, 5G) acts as its own Class II vapor retarder at ≥1.5 inches.

ThermoSeal HFO does not require an ignition barrier in attics or crawlspaces.

ThermoSeal 5G is NFPA 285 compliant for commercial wall assemblies on Type I–IV buildings.

Always confirm R-value requirements with your local building department; local amendments may apply.

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IECC 2021 Reference

Insulation Code Requirements
by Climate Zone

The 2021 International Energy Conservation Code (IECC) sets minimum R-value requirements for each US climate zone. Most states have adopted IECC 2021 or IECC 2018. Always verify with your local authority having jurisdiction (AHJ).

Climate Zone	Example States	Attic / Ceiling	Wall Cavity	Floor / Crawlspace	ThermoSeal HFO @ Min Attic
Zone 1	South FL, HI, PR	R-30	R-13	R-13	≈ 4.1" HFO
Zone 2	TX, FL panhandle, AZ, LA	R-38	R-20	R-19	≈ 5.2" HFO
Zone 3	GA, SC, NM, CA coast	R-38	R-20	R-19	≈ 5.2" HFO
Zone 4	VA, MD, OR, WA, KY, TN	R-49	R-20	R-19	≈ 6.7" HFO
Zone 5	NY, PA, OH, IL, MI, CO	R-49	R-20	R-30	≈ 6.7" HFO
Zone 6	ME, VT, NH, WI, MN, ND	R-49	R-20	R-30	≈ 6.7" HFO
Zone 7	N. MN, N. WI, MT, ID	R-49	R-21	R-38	≈ 6.7" HFO
Zone 8	Alaska	R-49	R-21	R-38	≈ 6.7" HFO

Sources: IECC 2021 Table R402.1.2. Wall values shown are for wood-frame wall cavity insulation only. Many jurisdictions allow trade-offs between assembly components. Contact your local building department for applicable code edition and local amendments.

Common Questions

R-Value FAQs

What R-value does spray foam provide per inch?

ThermoSeal 500 open cell provides R-4.1 per inch. ThermoSeal 800 open cell provides R-4.5 per inch. ThermoSeal HFO closed cell provides R-7.4 per inch. ThermoSeal 5G commercial closed cell provides R-7.3 per inch. All values are tested per ASTM C 518 and represent stabilized long-term R-values.

How does spray foam compare to fiberglass batts for R-value?

Standard fiberglass batts provide R-2.9 to R-3.8 per inch. ThermoSeal open cell spray foam provides R-4.1 to R-4.5 per inch, about 20–30% more insulating power per inch. ThermoSeal closed cell spray foam provides R-7.3 to R-7.4 per inch, roughly double the R-value of fiberglass per inch. Spray foam also provides continuous coverage with no gaps, voids, or thermal bridging, which fiberglass batts cannot match.

How thick does spray foam need to be to meet code?

It depends on your climate zone and application. For an attic in IECC Zone 4–8, the minimum is R-49. To reach R-49 with ThermoSeal HFO (R-7.4/in) you need approximately 6.6 inches. With ThermoSeal 500 (R-4.1/in) you need approximately 12 inches. Use the calculator above to find the exact thickness for any product and location.

Does spray foam R-value degrade over time?

ThermoSeal open cell (500 and 800) is totally water blown; the cells fill with air rather than a blowing agent gas, so there is no long-term R-value degradation. ThermoSeal HFO and 5G use Forane 1233zd HFO blowing agent, which has exceptional long-term stability. The R-values shown for ThermoSeal HFO and 5G are stabilized LTTR (Long-Term Thermal Resistance) values, not inflated initial values.

Is open cell or closed cell spray foam better for my climate zone?

In Climate Zones 1–4 (warmer climates), open cell is often sufficient for walls and attics, especially where R-value requirements are lower. In Climate Zones 5–8 (colder climates), closed cell is typically preferred for walls and roofs where thickness is limited; you get R-7.4/inch instead of R-4.1/inch, helping hit higher code minimums in tight cavities. Closed cell also provides a vapor barrier, which is especially important in colder climates where moisture control is critical. Open cell remains popular in all zones for interior walls and ceilings where sound control is a priority.

Spray Foam R-Value Calculator

Insulation Code Requirementsby Climate Zone

R-Value FAQs

Get the Right Thickness, Installed Right

Insulation Code Requirements
by Climate Zone