For each site that is adjacent to, or considered by the Planning Commission and Board of Supervisors to be visibly or environmentally detrimental to, the use of any structure used for residential, human habitation, sleeping, cultural, social, educational, recreational, religious or similar residential related purpose in any district, there must be preserved a strip of land for screening purposes on any side of the tract of land on which the residential or related use is situated. The preserved strip shall be a minimum of 20 feet in width. The required screen shall have a height adequate to achieve its purpose. Plant materials used for screening shall consist of dense evergreen plants. They shall be of a kind, or used in such a manner, so as to provide a continuous opaque screen within 24 months after commencement of operations in the area to be screened. The Board of Township Supervisors shall require that either new planting or alternative screening be provided if, after 24 months, the plant materials do not provide an opaque screen.