What determines the fire resistance rating of an exterior wall?
The fire resistance rating for exterior walls is based on construction type, occupancy and fire separation distance as defined in Section 6 of the IBC. These fire resistance requirements range from no required rating to 3 hours. Exterior walls generally have a rating based solely on interior occupancy use and structural requirements. However, exterior walls that are 10 feet or less from the property line are required to have a fire resistance rating based on the proximity to adjacent buildings and interior occupancy conditions. The 2009 IBC increased this distance from five to 10 feet.
How much glass can be used in an exterior wall opening?
Openings in an exterior wall typically consist of windows and doors. An exterior wall may or may not be allowed to have openings depending on the fire separation distance. When allowed, the codes distinguish between openings that are "protected" (fire-rated doors, windows, shutters) and "unprotected" (no fire rating). Tables 704.8 (2006 IBC) and Table 705.8 (2009 and 2012 IBC) lay out the percentage of protected and unprotected openings and size limits allowed in exterior walls. Click here to download 2012 IBC Table 705.8.
Fire protective glass, such as ceramics, wired glass and specialty tempered glass, is either limited in size or prohibited altogether, depending on the fire separation distance. Generally speaking, as the fire separation distance increases, the allowable opening area and the percentage of allowable fire protective openings increases.
Do the same limits apply to fire resistive glazing?
Does Table 705.8 (2009 and 2012 IBC) mean that you cannot have glazing in an exterior wall when the fire separation distance is less than 3 feet? No. Fire resistive glazing materials tested as part of a wall assembly, such as SuperLite II-XL by SAFTI FIRST, are allowed. Products such as SuperLite II-XL have been tested to the more stringent performance requirements of ASTM E119, which requires any temperature rise to be less than 250º F above ambient temperature on the non-fire side. Advanced products like fire resistive SuperLite II-XL glazing and SAFTIfire GPX framing and SAFTIfire CW framing allow building designers to exceed the opening protection limits restricting the use of fire protective glazing in fire doors and windows.
Where are the window or door opening rating requirements for exterior walls?
Once you've determined from Table 705.8 that protected openings are allowed, as well as the percentage permitted, you can go to Tables 715.4 and 715.5 (revised 2012 IBC Table 716.5 and 2012 IBC Table 716.6 ) to find the rating required for fire doors and windows in the exterior wall. Click here to download the 2012 IBC 716 Tables.
For example, exterior walls with a 1-hour rating require fire doors and window assemblies with a 45-minute rating. For 2 and 3-hour rated exterior walls, door and window openings must have a 90-minute rating. Sidelites and transoms that are part of a 90-minute door assembly in a 2 or 3-hour rated exterior wall, must be 2 or 3 hour rated, not 90 minutes.
Click here to read the full article on the IBC and fire rated exterior openings.