Praise be to Allah, The Lord of the Worlds.

Rental apartment isn`t liable for Zakah. Rather, the Zakah is due on the rental outcome once it reaches Nisab (Minimum amount liable for Zakah) and a full lunar year passes over receiving it. As for the apartment itself, it isn`t liable for Zakah. The evidence on this is that Abu Huraira reported Allah's Messenger (PBUH) as saying: "No Sadaqa is due from a Muslim on his slave or horse." {Agreed upon}. This narration indicates that a Muslim`s belongings aren`t liable for Zakah-whether they were intended for rental or not-unless they were bought to be sold, and this is the view the four Imams and what is reflected in Resolution No.(2, 2/2) issued by the International Islamic Fiqh Assembly which reads: 

"First: There is no clear text of Sharia that rental property and land are liable for Zakah.

Second: There is no clear text of Sharia that the output of rental property and land-excluding agricultural produce-are liable for instant Zakah. Thus, the Iftaa` Council decided what follows:

First: Rental property and land aren`t liable for Zakah.

Second: A quarter of a tenth is due on the produce as Zakah after a full lunar year passes over its reception, in addition other conditions , and that nothing prevents paying it (Zakah). " And Allah The Almighty Knows Best.