Exterior Wall Opening Limit by Fire Separation Distance (IBC Table 705.8)
How much of an exterior wall may be windows and doors, capped as a percentage of the wall area by the fire separation distance and by whether the openings are protected or the building sprinklered. A wall under 3 ft from the line gets none; at 5 to 10 ft a sprinklered wall may be 25% glass; at 30 ft or more there is no limit. The distance to the lot line, not the facade design, sets the glass - one of the strongest arguments for a sprinkler system on a wall tight to the property line. A design aid, not a code-official determination.
Formula and source
band = f(fsd_ft, protected) from Table 705.8; allowable_pct = band; allowable_area = band x wall_area (Infinity = no limit); pass = actual_opening <= allowable_area.
IBC 2021 Table 705.8 (maximum area of exterior wall openings) and ยง705.3 (measurement of the fire separation distance), by name.
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