We are running an office on a rented building to collect & distribute Zakath. Whether Zakath fund can be utilised to pay rent to this office?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

It is not permissible for you to spend any of the Zakah funds to pay the rent of the office or salaries of the employees working there. The eight legitimate channels of Zakah are clearly stated in the Quran; Allaah The Exalted says (what means): {Zakah expenditures are only for the poor and for the needy and for those employed to collect (Zakah) and for bringing hearts together (for Islam) and for freeing captives (or slaves) and for those in debt and for the cause of Allaah and for the (stranded) traveler - an obligation (imposed) by Allaah. And Allaah is Knowing and Wise.} [Quran 9:60]

Those employed to collect the Zakah are the workers appointed by the Muslim ruler to collect the Zakah. Ibn ʻUthaymeen said, “The Zakah officers are those employed by the Muslim ruler to collect, preserve and distribute the Zakah funds and the like.”

Shaykh Ibn Baaz said, “The workers employed to collect the Zakah are those appointed to collect it and travel all over the land to reach the towns and sources of water around which people live. They collect, preserve and administer the Zakah funds. They should be given wages in proportion to their effort according to the discretion of the leader.” [summarized]

Charities that are not authorized by the state to collect the Zakah are considered the Zakah-givers' personal representatives for collecting it and distributing it to the eligible recipients. They do not fall under the category of "those employed to collect Zakah" mentioned in the verse, and so no Zakah funds must be spent on such charities.

An-Nawawi said, “Imaam Ash-Shaafiʻi, and his companions (the Shaafiʻis) held that if the one who is distributing the Zakah is its owner or his representative, the share of the agent employed to collect it is waived and he must give it to the seven other categories (of people who are entitled to it).” [Al-Majmooʻ]

Allaah Knows best.