Abnormal stair width, must we bring it to current standards?

I have a 203k question

On a house built in the 30's; the stairs to the second floor, which has 3 rooms, is only 28" wide.  Can that be grandfathered in or will it need to be increased to 36".

Grandfathered...

Years ago I had one that had 10" stair treads, to correct it would have cut off the hallway and put you into the bathroom. HUD engineering told me it was grandfathered and we didn't have to bring it to current standards provided the stair treads were all uniform in height. 

I my instance the living area was clearly predicated on those upper rooms.