STI’s “Zero” Spandrel System

Apr 09, 2021 by Jonathan Matthews, CFPS, Fire Protection Engineering Manager

All vision glass curtain walls are becoming more popular as architects are designing these walls to
provide a modern and open concept for buildings. These buildings are aesthetically pleasing and result in unique and upscale designs. The difficulty firestopping all vision glass walls is there rarely is an area to properly install the firestop system and prevent it from being visible from the exterior of the building. So the question is how we properly maintain the life safety concern in the building while working within the design of the building.

One of the innovative perimeter fire barrier systems we have at STI is one that we call our “Zero” spandrel system. The Intertek System number is STI/BPF 120-03. The system uses a sheet metal pan attached to the upper transom and vertical mullions that hides the firestopping system at the floor line. The system does not require a lower transom therefore allowing the complete system to only be visible at the floor line. The pans can be painted or finished with a look that will be visibly pleasing from the exterior of the building. This system is a great option that only occupies a small area of the vision glass.

There are times though that the project design will not allow the installation of the system mentioned above. The International Building Code actually addresses all vision glass walls specifically. In section 715.4 the intersection of the floor assembly and the exterior curtain wall is addressed as follows:

714.4 Exterior Curtain Wall/Floor Intersection “Where fire resistance-rated floor or floor/ceiling assemblies are required, voids created at the intersection of the exterior curtain wall assemblies and such floor assemblies shall be sealed with an approved system to prevent the interior spread of fire. Such systems shall be securely installed and tested in accordance with ASTM E 2307 to provide an F rating for a time period at least equal to the fire-resistance rating of the floor assembly.

Exception: Voids created at the intersection of the exterior curtain wall assemblies and such floor assemblies where the vision glass extends to the finished floor level shall be permitted to be sealed with an approved material to prevent the interior spread of fire. Such material shall be securely installed and capable of preventing the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E119 time-temperature fire conditions under a minimum positive pressure differential of 0.01 inch (0.254 mm) of water column (2.5 Pa) for the time period not less than the fire-resistance rating of the floor assembly.”

This exception is not providing a rated joint condition but is intended to utilize materials that have known fire performance criteria. Through our extensive testing we know that our products are capable of preventing the passage of flame and hot gasses. To address this exception section of the code we have developed an IBC Exception letter to address this topic. In the letter we explain the code language in reference to the exception. The letter also describes the condition and the proper installation of the firestop material.

The acceptance of this letter will always fall upon the Authority Having Jurisdiction, but provides a degree of flexibility to designers for conditions that aren’t tested to ASTM E-2307 while still ensuring that some semblance of a system has been installed. Please contact Engineering Services if you have any questions.

Download PDF of Article Here