Itikaf in a Room inside the Mosque: Permissible?
Question

Is the doorkeeper’s room or the Zakah committee room inside the mosque considered suitable for i'tikaf? Please note that the doors of these rooms are inside the mosque.
Praise be to Allah.Rooms which are inside the mosque and whose doors open into the mosque come under the same ruling as the mosque. Based on that, it is permissible to observe i’tikaf in them because they are part of the mosque. 
But if the rooms are outside the mosque , then i’tikaf observed in them is not valid, even if the room has a door leading into the mosque.
For more, please see this category: I’tikaf.
And Allah knows best.