Why Are Corridors 5 Feet Wide?
Why are some doors recessed into the corridor? Why are some doors flush with the corridor? Why are most corridors 5’-0” wide? Why are some not?
In 2018 IBC 1005.3.2 Other Egress Components, anything not a stairway, is calculated by multiplying the occupant load by 0.2 inches. For a single corridor, 5’-0” (60”) divided by 0.2”/person equals 300 people. In most circumstances this is overkill. For example in an all (B) Business occupancy 300 people would occupy 30,000 square feet. More likely than not, there would be multiple corridors at that size floorplate, therefore, exacerbating the capacity. Then why 5’-0” wide?
In 2018 IBC 1020.2 Minimum Corridor Width states that the previous calculation governs, but minimum widths are stipulated in the identically named chart.
In an all (B) Business occupancy, unless the occupant load is less than 50, then the required minimum width would be 44” (3’-8”). So, then why 5’-0” wide?
Some corridor doors are recessed because in 2018 IBC 1005.7.1 Doors, “when fully open, shall not reduce the required width by more than 7”....” Where a typical required width is 3’-8” (44”) and a typical door is 3’-0” (36”) wide and the allowed encroachment when fully open, 90 degrees, is 7” then the corridor would need to be 6’-1” (73”) wide minimum, see figure 2. More commonly this would be articulated as a corridor of at least 4’-3” (51”) with a 2’-5” (29”) deep recessed door alcove, see figure 3.
Figure 2: 90-degree door without alcove.
Figure 3: 90-degree door with alcove.
2018 IBC 1005.7.1 does continue with “...and doors in any position shall not reduce the required width by more than one-half.” Consider a door with 180-degree hinges. Where a typical required width is 3’-8” (44”) and a typical door is 3’-0” (36”) wide and the allowed encroachment when fully open, 180-degrees, is only 7” and the door in any position can not reduce the required width by more than one-half. Then the corridor would need to be 4’-8” (58”) wide minimum. The next closest round number is 5’-0” (60”), see figure 4.
Additionally, in ICC A117.1-2009 404.2.3.2 a forward approach, and hinge side approach, on the pull side of a door require a perpendicular clearance of 5’-0” (60”), see figure 5.
Figure 4: 180-degree door, alcove not necessary.
Figure 5: 180-degree door with forward approach.
There are three reasons why most corridors are 5’-0” (60”) wide:
You could install 36” doors with 180-degree hinges and be compliant with both egress and corridor code.
It satisfies the most extreme door maneuvering clearances in accessibility code.
It’s a nice round number.
