I have read that cut stair stringers longer than 6 feet in length require mid-span support. Solid stringers seem to be able to get to about 13 feet without support. So how do you combine these two ideas when you are building 4 foot wide stairs and the two outside stringers are solid and the two inside stringers are cut?
Can that span the entire length unsupported, or does the presence of the two cut stringers bring you back to a maximum of 6 feet unsupported? In my case, the total rise will be about 8 feet or so, for stringers somewhere around the 13 feet mark.
Or is this simply a better-safe-than-sorry thing and you just support it always?