For smaller attic openings with a minimum measurement of 18 x 24 you will need to measure the swing clearance inside the attic space.
Attic access hatch minimum size.
The access opening should be located in a hallway or other readily accessible location and minimum 22 x 30.
An attic access opening runs between the ceiling joists whenever possible.
If the access is located in the ceiling the minimum unobstructed headrom above the opening must be 30 inches measured vertically at some point over the access.
If the attic space is smaller than these specs then an access hatch is not required.
The rough framed opening must be a minimum of 22 inches by 30 inches.
The 2007 california building code requires a minimum attic access opening of 20 inches by 30.
These specs are per r807 1 of the international residential code irc and the residential edition of the florida building code fbc.
Minimum vertical height of 30 inches measured from the top of the ceiling framing members to the bottom of the roof framing members.