Group dwellings with more than six occupants, such as hotels, motels, boardinghouses, family care homes, rest homes, convalescent homes or other similar residential uses, provided that such a group dwelling shall not be located within 300 feet of the boundaries of a parcel containing another group dwelling, unless a conditional use permit is issued on the basis that waiver of such separation requirement would not be materially detrimental or injurious to the property, improvements or uses in the immediate vicinity;