If under the IRC, a "flight" of stairs is defined as: "
FLIGHT. A continuous run of rectangular treads or winders or combination thereof
from one landing to another. " From:
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_2_sec002.htmUnderline is mine.
The risers can change height between flights but not vary individually by 3/8": "
R311.7.4.1 Riser height. The maximum riser height shall be 73/4 inches (196 mm). The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm)."
The treads can change depth, but vary by only 3/8" also; "
R311.7.4.2 Tread depth. The minimum tread depth shall be 10 inches (254 mm). The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Consistently shaped winders at the walkline shall be allowed within the same flight of stairs as rectangular treads and do not have to be within 3/8 inch (9.5 mm) of the rectangular tread depth. "
Which leaves us with the all-important
nosing (IF required, that remains the same at all flights between stories, if I understand this correctly);
"
R311.7.4.3 Profile. The radius of curvature at the nosing shall be no greater than 9/16 inch (14 mm). A nosing not less than 3/4 inch (19 mm) but not more than 11/4 inches (32 mm) shall be provided on stairways with solid risers. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm)
between two stories, including the nosing at the level of floors and landings. Beveling of nosings shall not exceed 1/2 inch (12.7 mm). Risers shall be vertical or sloped under the tread above from the underside of the nosing above at an angle not more than 30 degrees (0.51 rad) from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch diameter (102 mm) sphere.
Exceptions: 1. A nosing is not required where the tread depth is a minimum of 11 inches (279 mm). 2. The opening between adjacent treads is not limited on stairs with a total rise of 30 inches (762 mm) or less." Underline is mine, from:
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_par149.htm?bu2=undefined
Check locally with your AHJ.
Gary
P.S. Guide and definitions; flights-"Drawing 9", definitions- pp.18;
http://www.abqstair.com/wp-content/uploads/2012/06/SMAVisualInterpretationIRC2009ecopy_1__1_.pdf