See the california mechanical code for access requirements where mechanical equipment is located in attics.
Attic access code requirements.
Here s the full text of the code.
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.
Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that exceed 30 square feet 2 8 m2 and have a vertical height of 30 inches 762 mm or greater.
Your attic may presently have a fixed ladder a pull down ladder or no ladder at all.
When the access is located in a ceiling minimum unobstructed headroom in the attic space shall be 30 inches 762 mm at some point above the access measured vertically from the bottom of ceiling framing members.
When located in a wall the opening shall be a minimum of 22 inches wide by 30 inches high 559 mm wide by 762 mm high.
The rough framed opening.
When located in a wall the opening shall be a minimum of 22 inches wide by 30 inches high 559 mm wide by 762 mm high.
Where the access is located in a ceiling minimum unobstructed headroom in the attic space shall be 30 inches 762 mm at some point above the access measured vertically from the bottom of ceiling framing members.