Q: I rented a residential unit, but would like to use it for a workshop or office. Do I need the owner’s permission?
A: A renter should use the rental unit for the intended purpose and return it in the same condition in which he received it. He may not use the property for an alternate purpose that might damage it beyond the normal, expected wear and tear (C.M. 320:4).
If the tenant will repair any damage and restore the property to its original state, it seems permissible to use it for a different purpose, but the landlord can refuse if he fears this will require litigation. Similarly, the tenant is not allowed to use the property for an alternate purpose or leave it derelict if this will reduce future rental value (Kesef Kodashim 316:1; Maharsham 2:198).
The tenant may not make structural changes to the property without the landlord’s consent, unless the local custom allows making changes and restoring the property at the end of the rental period (Maharashdam, C.M. #292; Rema 314:2).