Fire-rated curtain wall
When the architects at Herman & Coliver: Architecture, San Francisco, began designing the addition of the east wing for the Jewish Home for the Aged in San Francisco, they had a clear vision, figuratively and literally. Integral to the design was a spacious glazed lobby that made a good fit with its historically significant surroundings, yet was clearly contemporary, signifying a place offering leading edge medical services. However, due to the proximity of this addition to the existing building, special fire requirements had to be met. The design team’s first challenge was to identify a 60-minute fire-rated window-wall system. Next challenge was to stay within budget.
The design team knew that fire-rated glazing products like ceramics existed, but was uncertain if they would meet the project criteria and were expensive. These products would include Safti First SuperLite C/P, TGP FireLite, Vetrotech Keralite and Schott Pyran. However, these products would not meet the 60-minute requirement of a fire-separation wall because ceramic products do not provide protection from radiant heat. The design team then started to explore other options.
Timing is everything
Safti First salespeople suggested a glass curtain wall to freely span an area almost 30 feet high. The sizes of the glass lites and vertical mullions of the frame would be carefully calculated to ensure that the structure would handle this unsupported span, while taking into consideration wind load, seismic drift and design criteria.
The outcome was the creation of an exterior 60-minute fire- and hose-stream rated window-wall system, curved horizontally and in elevation, using a SuperLite II-XL 60-minute fire-resistive glazing unit with an insulating glass-unit makeup of insulating clear low-emissive tempered glass. A total of 1,500 square feet of fire-rated, sound-abating insulating glass, with one-third of these units sandblasted to give a soft filtered lighting effect, was used. The glass lites ranged in sizes from 16 inches by 9 inches to 16 inches by 90 inches. A competitive fire-resistive filled glazing product that can provide similar performance is Contraflam, manufactured by Vetrotech. The SuperLiteII XL 60-minute glass lites were to be framed in an equally fire resistive-rated, water-tight custom-framing system that would afford maximum protection from the corrosive San Francisco fog and wet weather. The framing solution was Saftifire Frames, FireCW, a custom fire-resistive curtain wall.
The challenging climate conditions of the bay area include intense sun when not covered by fog. The need to allow soft daylight into the lobby while still having clear vision to the outside garden during these diverse conditions was important. The fire-rated units were also to be energy efficient and reduce noise from the adjacent roads to create a calm environment where the elderly could relax.
Criteria for exterior application
Fire-rated glazings are usually found in the interior where the threat of fire comes from inside the building. In this case, the fire rating was required for outside of the building as a result of:
• Another structure built within the same lot, as referenced in section 503.3 Buildings on Same Property in the California Building Code. In this case, the distance between the exterior wall and the existing building was greater than 20 feet but less than 40 feet, requiring the exterior window wall of this project to be fire rated for 60 minutes. This is to limit the spread of flames and fire that could develop from the radiant heat of a fire in either adjoining building.
• Close proximity to property lines.
• Thermal properties and energy efficiency. While the use of large areas of exterior glass allows daylight to enter a building, it also brings in heat. Insulating glass units were specified to limit the heat gain. The SuperLite II-XL 60-minute IGU selected was composed of an out board lite of 1⁄4-inch tempered glass on the No. 2 surface and with a low-emissivity coating a 1⁄4-inch spacer separating the low-e tempered glass and the fire-resistive glass unit. Much of the heat, either coming from direct sunlight or radiated from the surrounding buildings bounces off this surface and stays outside. The insulating attributes of the fire-resistive material in the unit provide superior energy performance with a U-value of 0.30. This low U-value allowed the project to meet California energy requirements and contributed to lowered energy consumption without sacrificing the airy well-lit design the team members required.
• Water penetration. To prevent rain and moisture from entering the building, the wall was designed to provide a water-tight seal to the exterior.
• Wind load and seismic drift. In all exterior glazing, wind load must be taken into consideration and in some locations, seismic drift is a factor. These factors applied to this project since the glass panels were to have an unsupported vertical span of greater than 28 feet, and the system would be located in a seismic zone. The engineering requirement was that the structure meet an L/240 deflection, allow for 1-inch vertical expansion and 1-inch side-to-side seismic movement.
• Acoustical properties. This addition would house medical clinics, research laboratories and administrative offices, so reducing traffic noise from the adjacent roads was important. The SuperLite II-XL 60-minute IGU used has a sound transmission rating of 49, and by placing this material in the exterior wall, a sound reduction of approximately 90 percent was achieved.
In an industry faced with ever-changing codes and the rapid advances in material technology, it is useful and time saving for designers to seek out expertise from a manufacturer when selecting fire-rated glazing.
Addition of east wing to the Jewish Home for the Aged, San Francisco
Owner: The Jewish Home for the Aged, San Francisco
Architect: Herman & Coliver: Architecture, San Francisco
Contractor: Turner Construction, Oakland, Calif.
Construction manager: Montgomery Corp., Petaluma, Calif., and Montgomery Capital Corp., San Francisco
Glazier: Guarantee Glass Inc., Richmond, Calif.
Glass: SuperLite II-XL 60-minute insulating glass unit
Framing: Saftifire Frames FireCW
Glass manufacturer and fabricator: SaftiFirst Fire Rated Glazing Solutions; San Francisco.