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.
Minimum attic access opening.
The minimum opening for the attic access should be 22 inches by 30.
The vertical height shall be measured from the top of the ceiling framing members to the underside of the roof framing members.
If the opening is located in a wall the 30 inch dimension must be vertical.
The access opening should be located in a hallway or other readily accessible location and minimum 22 x 30.
The rough opening cannot be less than 22 inches by 30 inches and must be located in a hallway or other readily accessible location.
Minimum vertical height of 30 inches measured from the top of the ceiling framing members to the bottom of the roof framing members.
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.
What is the minimum size for attic access opening.
The rough framed opening.
The 2012 international residential code requires an attic access opening for attics with an area greater than 30 square feet and a vertical height in excess of 30 inches.