Sometimes you cannot fully establish the present zoning usage from various record source so the agreement to purchase is structured so that you enter the intended zoning = 2 fam, three fam etc. Then if after a contract were accepted is would be subject to determining what the current zoning use actually is and if it is not what you preferred in the written contract you can end the sale agreement.. Often a residential property has been issued zoning variance for multi fam use but record research may or may not be acurate, expecially in Phila records. Usually the public record will say something like "converted to apt use, etc" In addition, if you were to putchase a mlti family dwelling the seller would have to provide a Use&Occupancy certificate that states the present use is legal. Also, the lending bank appraisal will require the same proof that the usage is permitted by zoning etc. Sometimes you have a situation where a single fam dwelling has legally been approved for change to 2 fam dwelling and later on a seller has changed it into a 3 or more dwelling but never received zoning approval. If the City becomes aware they will make them cease the illegal usage but the occurance of this same situation happining in Phila was not too uncommon in the past. Zoning enforcement and bank lending and appraisal requirements have pretty much forced those conversions to conform or revert back to allowable usage but there may still some long time ownership situation that has been flying under the radar in zoning violation?