Hello and welcome to Just Answer. I'm not sure what you are asking. Why is only one set required?
in a two story - single family residence you can have one set of stairs to the second floor with egress windows in the bedrooms some clients like to have a back set of stairs . The current house I'm working on has a problem in the framing so my backset of stairs don't fit if I could reduce my run to 9.1/4" it would fit
I'm working in Chester County PA outside of Philadelphia using 209 IRC if that helps
ment 2009 IRC
Yes...I understand your situation now. Unfortunately, all stairs have to meet the code requirements because in an egress situation, you never know which one is going to be used to make the emergency escape. The only thing I can recommend is that you look into using a stair with winder treads or even a spiral stair. They are a little more lenient code wise and you can usually get them to work where a typical stair won't.
no room for winders or spiral, thanks for looking into it, I might have another question down the line are you knowledgeable on wall brace as it applies to residential construction sec 602 in the 2009 IRC
In addition, verify that there are not any amendments to the code for PA, regarding stairs. My state uses the IRC for the basis of codes, but it has an amendment that allows a minimum of a 9 inch tread. It's just a thought and might be worth looking into with your local building department. Yes about the wall bracing, I am familiar with just about every code....I go through the book daily....let me know.