It's my understanding that if you have 3' wide treads and you put drywall on top you no longer meet code because your stair width is now 2-11". Is that also true for skirt board?
The skirt boards do not count. The drywall does, it needs to finish out at 36" or more. The framing needs to start at 37" for 1/2" drywall. If the drywall is thicker for some reason, the framing must be wider to accommodate.
According to IBC 2018 R311.7
Anything above the handrail height up until the headroom height needs to be a minimum of 36" wide. Anything at or below the handrail height the minimum width is 31.5" if there's one handrail or 27" if there are 2 handrails. As long as the skirt board isn't obnoxiously thick to reduce the width below 31.5" or 27" it's fine.
Do you have anything to support this? I believe this is correct but I haven't found anything to back it up in my searches. Nov 12, 2021 at 3:16
1It is in the code book It will take a few minutes, but I can add it to the answer Nov 12, 2021 at 3:19
codes.iccsafe.org/content/IRC2018/… Please go to R311.7 Stairways. I do not know how the get this page in the answer This is the actual building code site. Nov 12, 2021 at 3:27
I edited your answer with the link and my interpretation. Thanks. Nov 12, 2021 at 3:35
You did very well Nov 12, 2021 at 3:40