Understanding the Difference Between the Full NFPA 286 Test and the Attic / Crawl-Space Versions
(Aligned with ICC & AC12 — Editorially Revised June 2024)
When using expanded polystyrene (EPS) insulation, meeting fire-safety requirements is essential for both performance and code compliance. The NFPA 286 is the principal large-scale room-corner test method recognized by the IBC for qualifying materials used as exposed interior finishes. Under ICC AC12 (2024), the same test method applied with modifications also serves as the basis for evaluating foam-plastic assemblies in attics and crawl spaces. The latest ICC-ES Acceptance Criteria AC12 (June 2024) defines how foam plastic insulation, including EPS, may be qualified for these various uses. AC12 integrates NFPA 286 within its framework for both interior finish (exposed) applications and attic or crawl-space assemblies, establishing clear acceptance paths for each use.
Before Comparing NFPA 286 Tests:
How Codes Define Fire Protection for Foam Plastics
Before we examine the differences between the full and modified NFPA 286 tests, it’s important to understand how the code distinguishes between the types of fire protection required for foam plastics. The International Building Code (IBC) and ICC-ES AC12 define two key protective layers, thermal barriers and ignition barriers, each serving a specific purpose depending on the location and fire-risk level of the installation.
Understanding Thermal vs. Ignition Barriers
(IBC § 2603.4 / § 2603.4.1.6 and AC12 § 4.5.2, § 4.5.11.5)
Under the International Building Code (IBC 2024), foam plastic insulation such as EPS must be protected from fire exposure by one of two types of barriers, depending on where it is installed:
- Thermal Barrier – Defined in IBC § 2603.4, foam plastic must be separated from the interior of a building by ½-inch gypsum board or an approved equivalent. Equivalency is typically demonstrated by testing in accordance with NFPA 275 (the standard method for evaluating thermal-barrier performance) or by special approval under IBC § 2603.9, using large-scale tests such as NFPA 286 or UL 1715 in the end-use configuration.
- Ignition Barrier – Defined in IBC § 2603.4.1.6 and AC12 § 4.5.11.5, an ignition barrier provides a lower level of protection suitable for attics and crawl spaces that are not normally occupied and accessed only for service of utilities. AC12 Appendix A/B allows modified NFPA 286 testing to demonstrate “ignition-barrier equivalence,” meaning the EPS system resists early flame spread and ignition under limited-access conditions.
In short, in this case, thermal barriers are required for occupied interior spaces, while ignition barriers apply to unoccupied concealed spaces such as attics and crawl spaces where the fire exposure risk is reduced.
Full-Scale NFPA 286 Room Test
Exposed Interior Finishes
(Referenced in AC12 § 1.3.3.2.5, § 4.3, § 4.5.2)
Purpose
To evaluate how an EPS insulation system performs when exposed as an interior finish during a fully developed room fire. The test replicates realistic fire conditions to measure flame spread, heat release, and smoke generation on directly exposed EPS assemblies.
Relevance under AC12 (2024)
AC12 explicitly includes NFPA 286 (Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth) as a referenced standard for qualifying interior finish applications of foam plastics. Section 4.3 of AC12 further states that thermal barriers for foam plastics in non-bearing walls and ceilings, that is, exposed interior finishes, may be qualified using either NFPA 286 or UL 1715 room-corner testing, with acceptance conditions defined by IBC § 803.1.1 (2024).
Test Setup
EPS boards or EPS-based wall systems are installed:
NFPA 286 specifies three types of specimen mounting, depending on the application of the interior finish material (NFPA 286 5.12.). Also, specimens shall be mounted on a framing or support system that is comparable to that intended for their actual field use, using substrates, backing materials, insulation, or air gaps as appropriate to the intended application, and representing a typical value of thermal resistance for the wall system. (NFPA286, Chapter 5)
- The burner applies 40 kW for 5 minutes, followed by 160 kW for 10 minutes, totaling 15 minutes of exposure (NFPA 286 protocol).
Measured Parameters
• Flame spread across EPS surfaces
• Smoke generation and total heat-release rate
• Temperature rise within the room
• Occurrence of flashover* (complete room ignition)
Pass / Fail Criteria
According to IBC § 803.1.1.1, the EPS assembly must,
- During the 40kW exposure, no flame to the ceiling:
- No flame to the outer extremities of any wall/ceiling sample
- No flashover (per NFPA 286)
- Peak Heat Release Rate ≤ 800 kW
- Total smoke ≤ 1000 m²
Code Implication
A listed EPS assembly that meets IBC § 803.1.1.1 via NFPA 286 in the tested end-use configuration can be specifically approved under IBC § 2603.9, permitting installation without the prescriptive ½-inch gypsum thermal barrier, provided field installation matches the tested assembly.
Modified NFPA 286 Tests
Attics and Crawl Spaces
(Referenced in AC12 § 4.5.11.5 and Appendix A / B)
When EPS insulation is used in unoccupied concealed spaces such as attics or crawl spaces, the fire-load risk is significantly lower than in occupied rooms. To account for this, ICC-ES AC12 (June 2024) allows modified large-scale testing based on NFPA 286 to qualify these assemblies as ignition-barrier equivalents.
AC12 Provisions (2024 Edition) Section 4.5.11.5 of AC12 explicitly states:
“Within an attic or crawl space where entry is made only for service of utilities, foam plastic insulation shall be protected as set forth in IBC § 2603.4.1.6 or IRC § R303.5.3 / R303.5.4 […] As an alternative, the prescriptive ignition barrier shall not be required when satisfactory testing is conducted in accordance with Appendix A/B of this criteria.”
While both Appendix A and Appendix B outline acceptable test procedures, Appendix B is commonly used because it provides explicit, measurable acceptance criteria specifically, the average of the four recorded times must be ≥ 4 minutes 18 seconds.
Appendix B requirements (B2.1.4 to B2.1.6)
Mounting method B2.1.2:
The interior room dimensions as required by NFPA 286 shall be maintained. The fire test room shall be completely lined with one layer of 5/8-inch-thick (15.8 mm), Type X gypsum wallboard or 1/4-inch-thick (6.4 mm) glass-reinforced cement board. The foam plastic insulation shall be applied directly to the gypsum wallboard at the maximum thickness and density intended for use. The insulation shall be applied to the three test walls and the test ceiling. If a coating is used over the insulation, it shall be applied to both the walls and the ceiling at the same minimum thickness or coverage rate intended for use.
Test Data (B2.1.4)
During the test, the following parameters must be recorded:
- The time at which the heat-release rate exceeds 1 MW
- The time when heat flux to the floor exceeds 20 kW/m²
- The time when the average upper-layer temperature surpasses 600 °C
- The time when flames exit the doorway
Reporting (B2.1.5)
The test report must include:
- Type, average thickness, and nominal density of the foam plastic insulation
- Details (type, thickness, or application rate) of any coating used
- Each of the four recorded times above
- The average of those four times
Pass / Fail Criteria AC12 B2.1.6
The test is considered successful if the average of the four times (from § B2.1.4) is 4 minutes 18 seconds or greater, demonstrating that the EPS assembly can be used without a prescriptive ignition barrier in attics or crawl spaces, in accordance with AC12.
Final Takeaway
Both the full NFPA 286 test and the modified AC12 Appendix A/B versions serve to demonstrate that EPS insulation systems can be used safely and responsibly in accordance with modern code requirements.
- For exposed interiors, AC12 (§ 4.3 & § 4.5.2) mandates the full-scale NFPA 286 room-corner test, establishing compliance as an interior finish material without a thermal barrier.
- For attics and crawl spaces, AC12 (§ 4.5.11.5 and Appendix A/B) provides reduced-intensity NFPA 286-based options to verify ignition-barrier
By referencing the 2024 AC12 framework, designers, builders, and code officials can confidently select code-compliant EPS assemblies tailored to each specific application, ensuring safety, performance, and regulatory clarity.
*Flashover: is “the transition phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously, and fire spreads rapidly throughout the space. NFPA 286
