A house we are building (Habitat project) has the following basement stair
situation:

The total run of the stairs cannot exceed 115" because of headroom
issues--the state code requires minimum headroom of 6'8"=80 inches, and
there is a steel beam flange at 115" which is 85" above the floor. The
total height of the stairs is 103.5". With 13 steps, the rise per step is
7.96". There are 12 treads, and 115/12 = 9.58" run per step. The building
code requires at least a 10" tread, so stairs with 12 treads, a 7.96 rise
and a 10" tread with about 1/2" nose would work (the nose of the bottom
step would project slightly under the beam but nobody is going to care about
this).

However, these dimensions violate the "two risers + 1 tread = 24 to 25"
rule; you get 26, which is too large. My question: is a set of stairs with
these dimensions going to be uncomfortable or unsafe to use? I know that 8"
rise and 9" tread works just fine (that's what my stairs are), but I don't
know how it would feel if the treads suddenly grew an inch.