(1) A county may enact, enforce, or maintain an ordinance, development regulation, zoning regulation, or official control, policy, or administrative practice that authorizes the use of a residential dwelling, located in an area zoned for residential or commercial use, as a boarding home.

(b) Conform to lot size, building size, setbacks, and lot coverage standards applicable to the zoning district except if the structure is a legal nonconforming structure.

(3) A county may also require that the boarding home provider provide proof of written notification by the provider to the immediately adjoining property owners, informing the property owners of the intent to locate and maintain such a facility.

(4) Nothing in this section shall be construed to prohibit a county from imposing zoning or other conditions on the establishment and maintenance of a boarding home in an area zoned for residential or commercial use, including, but not limited to, restrictions on the number of residents.

(5) As used in this section, "boarding home" means any home or other institution, which provide board and domiciliary care, housing, and basic services in exchange for a fee or charge to up to sixteen unrelated permanent residents, and which assumes general responsibility for the safety and well-being of the residents in a residential structure located in an urban or rural residential zone. In order to qualify as a boarding home under this section, at least eighty percent of the permanent resident boarders must be fifty-five years of age or older. A boarding home shall be designed for supportive services in order for residents to live independently or semi-independently. A licensed in-home care agency may provide care as needed pursuant to chapter 70.127 RCW. A boarding home may be located adjacent to other boarding homes.