NFPA 285 Exterior Wall Fire Propagation
Summary
NFPA 285 is a full-scale fire test of an exterior wall assembly that measures how flames spread up and across the wall, through cavities, and from floor to floor. The building code requires it for walls with combustible insulation, weather barriers, or cladding in Types I through IV construction, so the whole assembly must be selected from tested or listed designs.
Cols
Scope
- Edition noted: NFPA 285, 2023; the 2024 IBC references the 2019 edition. Always verify the adopted code edition and local amendments for the project jurisdiction
- Covers the test method and its use through the building code's exterior wall provisions; it is a test of an assembly, not a material
- The 2023 edition widened the scope to buildings of any construction type, covering bearing and non-load-bearing assemblies, and added Annex B, a guide for extending test results to similar assemblies
- Fire resistance ratings of walls (ASTM E119 and UL 263) are a different test and are in the exterior walls and fire-resistance notes
Terminology
- Assembly test: a test of the wall as built (framing, sheathing, insulation, barrier, cladding), not of individual products
- Flame propagation: spread of flame over the wall face, through air gaps and cavities, and between floors
- Combustible component: insulation, weather-resistive barrier, cladding, or adhesive that can burn
- Water-resistive barrier (WRB): the weather barrier behind cladding; a combustible WRB may trigger testing
- Listed assembly: a tested wall design published by a third-party agency
- Engineering judgment (EJ) or analysis: an approved analysis extending test results to a similar assembly
- Metal composite material (MCM): metal skins bonded to a core
- Insulated metal panel (IMP): panels with insulating cores between metal facings
- Thermocouple: the temperature sensor used in the test
- Pass/fail criteria: the limits on flame travel and temperature set by the standard
Requirements
What the test measures
- NFPA 285 is an assembly test and is not a test of individual materials
- Flame propagation is assessed both vertically and horizontally across the exterior surface, through air gaps and cavities, and from floor to floor
- The result is pass or fail, recorded with dozens of thermocouples
Where the IBC requires it
- IBC 2024, Section 1402.5: combustible exterior wall coverings in Types I through IV construction are limited for vertical and lateral flame propagation (water-resistive barriers, metal composite material, EIFS, high-pressure laminate, foam plastic)
- IBC 2024, Section 1402.6: combustible water-resistive barriers on buildings over 40 ft in height comply with NFPA 285
- IBC 2024, Section 1402.7: metal-faced panels with veneers laminated to noncombustible cores with combustible adhesives are tested when installed on buildings over 40 ft
- IBC 2024, Section 1409: insulated metal panel systems, with distinctions between combustible and noncombustible cores
- IBC 2024, Chapter 26: foam plastic insulation in exterior walls; exemptions for insulated metal panels were clarified
- IBC 2024, Section 1402.8: compliance methods: direct testing of the specific wall assembly; a third-party listed assembly from an approved agency; or an approved analysis based on test results for a similar assembly that meets NFPA 285 acceptance criteria
Typical exceptions
- One-story buildings of Types I through IV may be exempt from the foam plastic NFPA 285 requirement
- Walls under 40 ft with a combustible barrier, and metal composite walls under that height, have exceptions in the code
Worked examples
Choosing a wall for a mid-rise
A 55 ft tall Type III-A building with brick veneer over foam plastic insulation, a combustible WRB, and steel studs.
| Step | Check | Result |
|---|---|---|
| Construction type | Type III exterior walls are noncombustible; combustible components are limited | NFPA 285 applies to the assembly |
| Height | 55 ft is over 40 ft | Combustible WRB requires compliance (Section 1402.6) |
| Compliance path | Section 1402.8 | Use a listed assembly that matches every layer, or an approved analysis |
| Substitutions | Change of insulation, WRB, or cladding | Re-verify against the listing |
Metal panel system
| Step | Check | Result |
|---|---|---|
| Product | Metal composite panels with a combustible core | Test or listing required over 40 ft |
| Alternative | Panels with a noncombustible core | Different path; confirm the code section |
| Documentation | Test report matching the assembly | Submit with the wall section |
Submittal checklist
| Item | Where it shows |
|---|---|
| Wall section with every layer and thickness | Detail drawings |
| Listing or report number | Specification and submittal |
| Fastening and cavity details | Details and shop drawings |
| Fire barrier at floor edge | See the perimeter fire containment detail |
Coordination
- Wall assembly selection: choose an assembly with an existing listing or test early; custom assemblies need testing or an analysis
- Product substitutions: a change of insulation brand, WRB, or cladding can invalidate the listing; control substitutions in the specifications
- Building envelope consultant: envelope designers track listings and analyses
- Approvals: the building official accepts the listing or analysis at plan review
- Thermal performance: continuous insulation thickness and cavity design tie to the energy code
- Curtain wall and spandrel: perimeter fire containment at floor edges is a separate detail
- Cost and schedule: testing is costly and slow, so listings give design flexibility
Common issues
- Assuming product tests suffice: the test covers the whole assembly
- Wrong edition: the code references the 2019 edition, and listings may be to later editions
- Substitutions after approval: a different foam or WRB invalidates the evidence
- Analysis not accepted: an engineering judgment needs the approval of the building official
- Exterior insulation added in retrofit: applying combustible insulation on an existing building without a check
- Height threshold missed: the 40 ft rule applies to specific components, not all
Standards
- NFPA 285: standard fire test method for evaluating fire propagation characteristics of exterior wall assemblies containing combustible components
- ASTM E119 and UL 263: fire resistance tests for wall ratings
- ASTM E84 and UL 723: surface burning characteristics of materials
Sources
- ICC Building Safety Journal: beyond the wall, decoding the 2024 IBC and NFPA 285 fire safety evolution, https://www.iccsafe.org/building-safety-journal/bsj-dives/beyond-the-wall-decoding-the-2024-international-building-code-and-nfpa-285-fire-safety-evolution/
- GoCodebook: 2025 California Building Code, Chapter 14 exterior walls (based on the 2024 IBC), https://gocodebook.com/library/us/ca/ca-building-code