(a) The requirements of this article shall apply to the construction, alteration, repair, use, maintenance, and occupancy of permanent buildings and commercial modulars in parks. The provisions of this article relating to permanent buildings and commercial modulars in parks do not apply to accessory buildings or structures or building components established for use of an occupant of a unit. The department shall administer and enforce all of the provisions of this article relating to permanent buildings and commercial modulars in parks except in a city, county, or city and county, which has assumed responsibility for enforcement of Division 13, Part 2.1 of the Health and Safety Code and this chapter.

(b) Existing construction, connections, and installations of plumbing, electrical, fuel gas, fire protection, within permanent buildings or commercial modulars in parks, made before the effective date of the requirements of this chapter, may continue in use so long as they were in compliance with requirements in effect at the date of their installation and are not found to be substandard.