(California Building Code Chapter 5) 

The height of a structure is the vertical distance from the average level of the highest and lowest point of the natural grade of that portion of the building site covered by the structure, to the topmost point of the structure, but excluding certain features, such as chimney, vents, and other mechanical appurtenances. (Reference Section 21.06.630, Title 21, Monterey County Code).

Example of Height of Structure