I just ran into an interesting situation recently. I had designed a set of exterior open grate metal stairs per the building code but the steel fabricator decided to construct them in another way. They will remain nameless to "do no harm". I received a phone call from the superintendent saying that the building inspector "dinged" us on these stairs during his inspection. So of course I asked if they were designed and installed per the architectural drawings. His response of course was "NO". What was missing? A simple piece of angle or bar stock should have been welded to the back side of the tread to prevent a 4" sphere from passing through the riser. The story ends with the fabricator resolving the issue on his own dime, unfortunately for them.
Most stairs are required to meet IBC provisions, except a choice few exceptions in an Industrial, Utilitarian, I-3, or other specified occupancies. Ships ladders and cage ladders are allowed in very specific circumstances, but must follow OSHA requirements.
The stairs in the above story were designed in accordance with 2006 IBC. The specific section that deals with stair risers is IBC 1009. If you read this section you'll notice there are different requirement for handicapped accessible stairs and non-handicapped accessible stairs, which I'll call "standard stairs".
Standard stairs require that a 4" sphere not pass through the riser per IBC section 1009.3.3 exception 1. In my opinion, this is a life safety provision- to prevent your foot from getting too far back on the tread and getting your toe caught on the tread above and having a less than thrilling spill. I have worked with a few stair detailers/fabricators that knew of the code provision, but did not follow it unless specifically asked to... and one who apparently didn't care to follow directions at all. This is rather alarming to me, so I try to do my best at checking shop drawings and communicating this code requirement clearly; I suggest the same to anyone else.
Handicapped accessible stairs require closed risers- no exceptions. What stairs have to be accessible? Due to length and content, I will cover that subject in a separate article entitled "Accessible Stairs". But be sure that YOU know, or else I see change orders in your future :)
So if a detailer/fabricator tells you that you don't need the angle or plate on the back of your stair tread (when you know it’s required) please educate them... It will improve both of your lives!
