The short answer
In the 2021 International Residential Code, spray foam falls under Section R316 (Foam Plastic). Foam generally has to be separated from living space by a 15-minute thermal barrier such as 1/2-inch gypsum board (R316.4). In attics and crawl spaces entered only to service utilities, a lighter ignition barrier is allowed instead (R316.5.3 and R316.5.4). Products tested under ICC-ES acceptance criteria AC377 Appendix X can omit or replace those barriers under the conditions in their evaluation report. Other sections govern unvented attics (R806.5), crawl spaces (R408), vapor retarders (R702.7) and required R-values (IECC Table R402.1.3). The 2024 IRC renumbers the foam plastic section to R303, and states and cities adopt different editions with their own amendments.
How the codes apply to spray foam
Spray polyurethane foam (SPF) in houses is regulated mainly by two model codes from the International Code Council (ICC):
- International Residential Code (IRC). Covers fire safety of foam plastic (Chapter 3), roof and attic assemblies (Chapter 8), foundations and crawl spaces (Chapter 4), and wall coverings, including vapor retarders (Chapter 7).[1][2]
- International Energy Conservation Code (IECC). Sets minimum R-values. The same residential tables appear in IRC Chapter 11, so IECC Table R402.1.3 is also IRC Table N1102.1.3.[10]
Model codes have no force until a state or local government adopts them, often with amendments. Some jurisdictions still enforce the 2018 or 2021 editions, while others have adopted 2024. This page uses 2021 IRC/IECC section numbers and notes where the 2024 edition changes them. Always confirm the edition and amendments with your local building department.
2024 renumbering. In the 2024 IRC, the foam plastic section moved from R316 to R303. An ICC-ES report covering both editions cross-references them: thermal barrier 2021 R316.4 = 2024 R303.4, attic and crawl-space ignition barriers 2021 R316.5.3/R316.5.4 = 2024 R303.5.3/R303.5.4, and termite provisions 2021 R318.4 = 2024 R305.4.[3]
IRC R316: foam plastic fire rules
| 2021 IRC section | What it covers |
|---|---|
| R316 (labeling provision) | Labeling and identification of foam plastic; evaluation reports set what the label must show[3] |
| R316.3 | Surface burning: flame spread index ≤ 75 and smoke-developed index ≤ 450 (ASTM E84) at the thickness used[7] |
| R316.4 | Thermal barrier between foam and the interior[3][4] |
| R316.5.3 / R316.5.4 | Ignition barrier in attics / crawl spaces[3][4] |
| R316.6 | Specific approval of alternate assemblies based on testing[4] |
Labeling and identification
Foam plastic must be labeled so an inspector can identify it. In practice, evaluation reports require the product label to carry the ICC-ES mark or report number, along with the manufacturer, product name, density and fire-test indices.[3] The same report requires jobsite insulation certification and labeling under IRC N1101.10.1 and N1101.10.1.1 (IECC R303.1.1 and R303.1.1.1).[3]
Thermal barrier (R316.4)
Foam plastic must be separated from the interior of the building by an approved thermal barrier. The prescriptive choice is 1/2-inch gypsum wallboard. NFCA notes that the IRC also allows a wood structural panel option, a material that meets NFPA 275, or a product-specific approval.[4][3] The barrier is meant to delay the foam’s temperature rise and its involvement in a fire.[4]
Ignition barrier in attics and crawl spaces (R316.5.3, R316.5.4)
Where an attic or crawl space is entered only to service utilities, the code allows a lighter ignition barrier in place of the thermal barrier. The prescriptive ignition-barrier materials are:[4][5]
- 1-1/2-inch mineral fiber insulation
- 1/4-inch wood structural panels
- 3/8-inch particleboard
- 1/4-inch hardboard
- 3/8-inch gypsum board
- Corrosion-resistant steel, 0.016 inch base-metal thickness
ACC points out that ignition barriers are not required to meet the 15-minute thermal-barrier performance test.[5] If the attic is used for anything beyond servicing utilities, such as storage, a thermal barrier applies instead. Duluth’s handout spells this out for Minnesota’s adoption.[7] The attic or crawl space itself must still be separated from the living space by a thermal barrier.[3] For how this plays out in practice, see attic spray foam and crawl space spray foam.
ICC-ES evaluation reports and AC377 Appendix X
Most spray foams are approved through an evaluation report (ESR) from ICC Evaluation Service, which checks a product against an acceptance criterion. For spray foam that criterion is AC377, Acceptance Criteria for Spray-Applied Foam Plastic Insulation.[5] ESRs are advisory. Only the code official grants final approval.[5]
Appendix X of AC377 is a modified NFPA 286 room-corner fire test developed with the Spray Polyurethane Foam Alliance. It lets a supplier qualify an attic and crawl-space assembly in a single test, either bare foam or foam covered by an alternate ignition barrier such as an intumescent coating.[5] The coating has to be applied uniformly to walls and ceilings in the test.[5] NFCA cautions that these approvals are product-specific: a coating approved over one foam isn’t automatically approved over another.[4]
A current report shows what the conditions look like. One 2025 ESR allows its foam in attics and crawl spaces without a prescriptive ignition barrier only when all of the following apply:[3]
- Entry is only to service utilities, and there’s no storage.
- The space isn’t interconnected with other attic or crawl spaces.
- Its air isn’t circulated to the rest of the building.
- Ventilation or unvented-attic rules are met.
- Combustion air is provided.
- Hot-work precautions are observed.
- An installation certificate is posted at each entrance listing the product, thickness, manufacturer and installer.
The same report sets a specific coating at a minimum film thickness and limits foam thickness.[3] Read the report for your product, not a generic summary.
R806.5: unvented attics
The IRC permits unvented (conditioned) attics and unvented rafter assemblies when a list of conditions is met. Duluth’s summary of Minnesota’s adoption includes these:[7]
- The attic is entirely within the building thermal envelope.
- No interior Class I vapor retarder is installed on the ceiling side.
- Air-impermeable insulation, such as spray foam, is applied in direct contact with the underside of the roof sheathing.
- In colder climate zones, air-impermeable insulation must also act as, or be covered by, a vapor retarder. Duluth’s handout states the climate zone 7 rule as a Class II vapor retarder or a Class III coating or covering. Check your adopted wording.
Where rigid board goes over air-impermeable insulation, 2021 IRC Table R806.5 sets minimum condensation-control R-values. The insulation must also meet the IRC N1102 energy requirements.[6]
| Climate zone | Minimum rigid board on air-impermeable insulation |
|---|---|
| 2B and 3B, tile roof only | None required |
| 1, 2A, 2B, 3A, 3B, 3C | R-5 |
| 4C | R-10 |
| 4A, 4B | R-15 |
| 5 | R-20 |
| 6 | R-25 |
| 7 | R-30 |
| 8 | R-35 |
Design choices are covered in vented vs unvented attic spray foam and spray foam roof deck insulation.
R408: crawl spaces
Section R408 covers under-floor spaces. For unvented crawl spaces (R408.3), the model text requires:[8]
- Exposed earth covered with a continuous Class I vapor retarder, with joints overlapped 6 inches and sealed, and edges run at least 6 inches up the stem wall.
- One of the following: continuous mechanical exhaust at 1 cfm per 50 square feet; a conditioned air supply at the same rate; use as a plenum in existing structures; or dehumidification sized to the manufacturer’s specifications.
- Perimeter walls insulated per the energy provisions when using the exhaust or supply options.
Spray foam on crawl-space walls still falls under the R316.5.4 ignition-barrier rule unless the product’s evaluation report allows otherwise.[3] States amend R408.3 too. Minnesota’s 2025 proposal is one example.[8]
R702.7: vapor retarders
The 2021 IRC defines vapor retarder classes in Table R702.7(1):[9]
| Class | Perm rating | Examples in the table |
|---|---|---|
| I | ≤ 0.1 | Sheet polyethylene, nonperforated foil |
| II | > 0.1 to ≤ 1.0 | Kraft-faced batts, vapor retarder paint |
| III | > 1.0 to ≤ 10 | Latex or enamel paint |
A Class I or II interior vapor retarder is typically required in climate zones Marine 4 and 5 through 8. Class III is allowed where continuous-insulation conditions in Table R702.7(3) are met, and Table R702.7(4) sets when Class II may be used with continuous insulation.[9] Whether a given spray foam layer counts as a particular class depends on its tested perm rating at that thickness. Check the product’s data sheet and evaluation report.
IECC R402: how much insulation
The prescriptive R-values are in Table R402.1.3 (Insulation Minimum R-Values and Fenestration Requirements by Component). Table R402.1.2 holds the U-factor alternative.[10] In the 2021 edition, the ceiling requirement is R-30 in climate zones 0–1, R-49 in zones 2–3, and R-60 in zones 4–8. A wood-frame wall in zone 4 (except Marine) needs R-30, R-20 + 5ci, R-13 + 10ci, or R-0 + 20ci.[10] Spray foam meets these with its labeled R-value at the installed thickness, documented through the jobsite certification noted above.[3]
Many jurisdictions amend these tables or offer alternative compliance paths, so check the local version.
What to ask your installer and inspector
- Which IRC/IECC edition and local amendments apply to this permit?
- Which ESR covers the product, and which section allows the planned barrier, or the lack of one?
- What climate zone are we in, and what do R806.5 and R402.1.3 require here?
Turn these into a full interview with our contractor questions checklist, or find installers in the directory.
Questions owners ask
Does spray foam have to be covered by drywall?
Usually. In the 2021 IRC, foam plastic must be separated from the interior by an approved thermal barrier, and 1/2-inch gypsum board is the common prescriptive choice (R316.4). Exceptions exist for some attics and crawl spaces, and for products whose ICC-ES evaluation report shows they passed specific fire tests with or without a tested coating.
What is the difference between a thermal barrier and an ignition barrier?
A thermal barrier separates foam from occupied space and must meet a 15-minute fire-performance standard. An ignition barrier is a lighter covering allowed only in attics and crawl spaces entered for servicing utilities. The prescriptive options include 1-1/2-inch mineral fiber insulation, 1/4-inch wood structural panels and 3/8-inch gypsum board.
Can spray foam be left exposed in an attic?
Only if the specific product, sometimes with a specific coating, has been tested and approved for that use, typically under ICC-ES AC377 Appendix X. Even then, the evaluation report's conditions apply, such as entry only for utility service, no storage and a posted installation certificate. Ask the installer for the report and the exact section that allows it.
Which code edition applies to my house?
Whatever edition your state or local government has adopted, with its amendments. Many places are on the 2018 or 2021 IRC, and some have moved to 2024. Your local building department can tell you which edition and amendments apply to your permit.
Sources
- 2021 International Residential Code (IRC), Chapter 3 Building Planning, International Code Council. Accessed October 19, 2026. Official ICC Digital Codes page for the chapter containing Section R316 Foam Plastic. Code text loads in an interactive viewer and could not be read by our tools, so section numbers below were cross-checked against ICC-ES reports and adoption documents.
- 2021 International Residential Code (IRC), Chapter 8 Roof-Ceiling Construction, International Code Council. Accessed October 19, 2026. Official ICC Digital Codes page for the chapter containing Section R806.5. Same viewer limitation as above.
- ICC-ES Evaluation Report ESR-5370 (spray-applied open-cell foam insulation), ICC Evaluation Service. Accessed October 19, 2026. Reissued September 2025. Cross-references 2024 IRC R303 to 2021 IRC R316 numbering; cites AC377 (June 2023, editorially revised June 2024) and Appendix X. Cited as an example only.
- Thermal & Ignition Barrier Requirements for Foamed Plastic, National Fireproofing Contractors Association (NFCA). Accessed October 19, 2026. Webinar slide deck dated July 2025. Lists IRC R316 thermal-barrier options and prescriptive ignition-barrier materials.
- Know the Code: Using Spray Foam Insulation in Attics and Crawl Spaces, American Chemistry Council, Center for the Polyurethanes Industry. Accessed October 19, 2026. Dated October 2009. Background on ICC-ES evaluation reports and the origin of AC377 Appendix X (SPFA room-corner protocol).
- Unvented Roofs for Conditioned Attics: Solutions That Work (BI509), Insulation Institute (NAIMA). Accessed October 19, 2026. Published May 2026 by the fiberglass and mineral wool trade group. Reproduces 2021 IRC Table R806.5.
- Residential Unvented Attic Assemblies (handout 164), City of Duluth, Minnesota, Construction Services & Inspections. Accessed October 19, 2026. Local building-department handout (document code 164-vD1225) summarizing Minnesota Residential Code R806.5, R316.3, R316.4 and R316.5.3. An example of a state adoption.
- Code Change Proposal: IRC R408.3 Unvented crawl space, Minnesota Department of Labor and Industry. Accessed October 19, 2026. State technical advisory group handout dated August 27, 2025, reproducing the model R408.3 text as the base for a proposed amendment.
- Interior Vapor Retarder Requirements with ZIP System R-sheathing (HUB 9311), Huber Engineered Woods. Accessed October 19, 2026. Manufacturer technical note dated November 22, 2024. Reproduces 2021 IRC Tables R702.7(1), R702.7(3) and R702.7(4). Cited for the code tables only.
- 2022 Committee Action Hearing Results, REPI-33-21 (2021 IECC Tables R402.1.2 and R402.1.3), International Code Council. Accessed October 19, 2026. ICC code-development document (2022) showing 2021 IECC Table R402.1.3 (Table N1102.1.3) as the base text for a proposed change.