Why do we call a single building the premises ?

Why do we call a single building the premises ? 

 

To answer this question, we must go back to the Middle Ages. But first, let it be noted that premises  comes from the past participle  praemissa,   which is both a feminine singular and a neuter plural form of the Latin verb praemittere,  "to send in advance, utter by way of preface, place in front, prefix."  In Medieval Latin the feminine form praemissa  was used as a term in logic,  for which we still use the term premise  descended from the Medieval Latin word  (first recorded in a work composed before 1380). Medieval Latin praemissa  in the plural meant "things mentioned before"  and was used in legal documents, almost always in the plural, a use that was followed in Old French and Middle English, both of which borrowed the word from Latin. A more specific legal sense in Middle English, "that property, collectively, which is specified in the beginning of a legal document and which is conveyed, as by grant," was also always in the plural in Middle English and later Modern English. And so it remained when this sense was extended to mean "a house or building with its grounds or appurtenances," a usage first recorded before 1730.