Apartments in base game worlds

Hello! Unfortunately I don't believe that is possible without a pack. Now, of course it's possible to live in an apartment the only issue is other sims from the "City Living" pack or from any other pack (or the base game sims). won't be able to live in the same building. If you install some type of mod with apartments (there must be one out there somewhere) then you could change the lot type to apartment and other sims could live right next door! Anyway, hope I helped. Happy Simming! -@powers6180