*This is part of a continuing series on rainscreen façades, for an overview of rainscreens please see the first article in the series.

Why fire considerations are different for rainscreen façades compared to curtain wall

An important part of every building design is fire protection. There is a heavy focus on maintaining internal partitions to prevent smoke and fire from moving throughout the building, but there can be some confusion when designing the façade. ASTM E2307 and NFPA 285 are two fire tests that relate to façade design, but for very different purposes. ASTM E2307 relates to fire joint assemblies, commonly between curtainwall glazing and a floor slab. Whereas NFPA 285 pertains to the combustibility of a wall or façade assembly. For some projects a designer will need to consider both the joint between the exterior wall and the floor slab with ASTM E2307, and the exterior wall itself by NFPA 285. When discussing rainscreens, we will focus on NFPA 285. 

NFPA 285, Standard Fire Test Method for Evaluation of Fire propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components

NFPA 285 is a standard test designed to understand how the materials used in a façade can contribute to flame and smoke spread. This can be important in a fire event, where the fire can breach an exterior window, and spread up and down the façade, or around partitions if the materials are not properly protected.

The test is completed with a 30-minute burn, and is a pass-fail criteria based on how flames and rising temperatures spread as seen below. 



NFPA 285 considerations depend on the project 

Model building codes recognize that the concern of fire propagation changes based on the materials that are used, and the type and size of the building. Eliminating or protecting combustible materials can remove the need to have an NFPA 285 certified system. These considerations can become very important to a designer as various parts of a façade are chosen. The type of insulation and panel are critical. Additionally, many bracket/clip systems rely on the use of mineral wool to cover and protect the clips from fire exposure. 



NFPA 285 is a system test, individual components are not certified

Testing reports following the NFPA 285 criteria rely on the entire buildup of the façade. The base material, insulation, substructure, panel type, and ventilation cavity are all relevant variables that must match the testing criteria. A component on its own may provide some combustible material, but not enough to make the entire system fail the test. This can create difficulties in finding a system, as there is a wide variety of façade products throughout the entire application. 

Two methods for compliance

NFPA285 provides two paths to compliance: analytical and evaluation protocols. The analytical process is simple, build a façade section based on the testing criteria and test the flame response. The evaluation protocol, while more complicated, allows for a wider range of replacement products. In this method, products are tested compared to those that they would replace to understand if they contribute to the spread of fire in a façade. Using this data and an understanding of fire science, engineering judgements can be made about the suitability of a product replacement with a system that passed the analytical process. 

Design with Hilti Support

The Hilti system has been tested by a third-party consultant following the evaluation protocols, for use when replacing a bracket from a NFPA 285 certified system. For further explanation on the evaluation protocol, and to see the consultant's report, please contact our Façade specialist teams (link to façade landing page).
 
Hilti is ready to support your façade design project needs.
 
Hilti Engineers can support you with:
-       Attachment solutions for most common base materials and panel types
-       Cladding view plans
-       R value calculation in accordance with ISO 6946 and ISO 10211
-       Structural design of the substructure according to IBC/NBC requirements
-       Design of fastening based on sub material, possibility of pull-out tests in the field
-       Installation documentation and training on site 
 
To contact our façade consultants to discuss your project needs please visit our request form
For more information on simplifying your design process, see our article
For more information about rainscreen performance in fire, see our article on NFPA 285
For more information on how rainscreens can provide protection from noise pollution, please see our article on acoustic testing