The cavity wall conundrum

NFPA 285 compliance
Perhaps the most vexing element of building envelope design is compliance with NFPA 285. As defined by the National Fire Protection Association, the standard is a “Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-loadbearing Wall Assemblies Containing Combustible Components Using the Intermediate-Scale, Multi-story Apparatus.” (Prior to its IBC adoption in 2000, a similar, larger-scale test appeared in the 1988 Uniform Building Code [UBC].) The code applies to Type I through Type IV construction on multi-story projects, or single-story walls in excess of 12 m (40 ft).

The defining characteristic of NFPA 285 is it is an assembly test, just like an Underwriters Laboratories (UL) or Factory Mutual (FM) roof assembly test. A manufacturer may market an air barrier as “fire-resistant” or “fire-rated,” but such designations have no bearing on compliance with NFPA 285. Complicating matters, there is no single clearing house to provide designers with tested and passed assemblies.

In the late 1980s, NFPA required exterior insulation and finish system (EIFS) manufacturers to test their systems. Other foam plastic insulation manufacturers (e.g. those involved with extruded polystyrene [XPS]) have been vigilant with their testing for years, and have very thorough reports of assemblies with which their products comply. In the 2012 IBC, AWBs had to comply with Section 1403.5, as all AWBs are combustible. However, when some states and the District of Columbia adopted the 2012 IBC, they excluded 1403.5.

According to the 2015 IBC, 1403.5 can be excluded if the AWB is the only combustible component in the assembly. The 2015 IBC also specifies if the AWB falls below a certain level of fuel contribution (based on ASTM E84 Class A and ASTM E1354, Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter) and it is the only combustible component in the assembly, it will not require NFPA 285 compliance. Further, rough opening flashings associated with the AWB system are also excluded from NFPA 285 compliance requirements.

Clearly, verifying compliance with NFPA 285 can be complicated. Nevertheless, doing so is an essential element of modern building safety.

Solving the conundrum
While each of the preceding topics could be expanded into an article of its own, they are highlighted here to help make building designers aware of the competing requirements and standards involved in modern cavity wall design. Ultimately, designers should know continuous air barriers and insulation, along with NFPA 285, are code compliance issues, which must be balanced with the goal of keeping water out of the building.

Achieving this balance will help designers go a long way toward designing the safest, most effective building envelope possible and thus solve the cavity wall conundrum.

Todd C. Skopic, CSI, CDT, LEED AP, is a building science manager at Henry. He has been in the air barrier industry for 16 years, working with different manufacturers. Skopic is active in CSI, BEC, RCI Inc., and ASTM, and serves on the Terminations and Flashings Committee for the Air Barrier Association of America (ABAA). He can be contacted via e-mail at


Leave a Comment


Your email address will not be published. Required fields are marked *