All drawings and specifications shall be prepared under the responsible charge of an architect, civil engineer, or structural engineer, who shall sign all drawings and specifications for approval of the enforcement agency. Observation of the work of construction shall be under the general responsible charge of the same architect, civil engineer, or structural engineer when feasible, as determined by the enforcement agency, except that if drawings and specifications do not involve architectural or structural conditions, the drawings and specifications may be prepared and the work of construction may be administered by a registered professional engineer qualified in the branch of engineering that is appropriate to the drawings, specifications, estimates, and work of construction.