Code provisions on this point have flip-flopped in recent years. The 2012 IBC limited projections to no less than 2 feet from the property line if the fire separation distance (FSD, usually the distance from the exterior wall to the property line) was less than 5 feet, or no less than 40 inches to the property line when the fire separation distance was 5 feet or greater. The 2015 IBC took a detour and set the minimum projection distance at “24 inches plus 8 inches for every foot of FSD beyond 3 feet or fraction thereof” beginning at an FSD of 3 feet, which resulted in much greater restrictions. Then, the 2018 IBC dropped this formula and went back to the 40-inch limit when the building had an FSD of at least 5 feet but kept the formula for buildings with an FSD between 3 feet and less than 5 feet. And most recently, a 2021 IBC change will strike the “old” formula for buildings with an FSD from 3 to less than 5 feet and will replace it with “2/3 the FSD” (see ICC code change FS14-18).
Bottom line? The 2021 IBC will be only slightly more restrictive on the proximity of commercial building projections to the property line than the 2012 IBC, and only for buildings with an FSD from 3 to less than 5 feet. Keep in mind that combustible projections extending to within 5 feet of the property line must be of 1-hour construction, heavy timber, or fire-retardant-treated wood. There’s an exception to this for Type V-B construction with an FSD of at least 5 feet (see 705.2.3 of the 2018 IBC).