Provided that, where two or more adjoining holdings held by the same owner form part and parcel of the site or premises of an apartment and a dwelling house, manufactory, warehouse, or place of trade or business, such holdings shall be deemed to be one holding for the purposes of this Act. Provided further that where any building is capable of being enjoyed separately in parts, or where portions of such building are owned separately by different persons, or where the building comprises self-contained and independent units, each of such parts, portions or units shall, on application by the owners, be deemed, to be a separate holding.