The new rules make it compulsory for landlords to obtain planning permission when converting a property into an HMO.
This will apply to family homes in the C3 category that are being changed into small HMOs for three to six people, or C4s.
Landlords have also been directed to declare details of all existing small HMOs in the area.
The Council consulted on introducing the Article 4 Direction last year.
This year it wrote to landlords, saying: “If you are the landlord of an existing small HMO, we are asking that you declare this to us and provide details of the address of the property and any evidence to show that it is an existing HMO.”
“This will ensure that we have as much information as possible about existing HMOs in the city before the Article 4 Direction becomes enforceable. The process for declaring existing HMOs will remain open until the Article 4 Direction comes in to force on Monday 8 June 2020,” it said.
In October 2018, central government introduced a new, UK-wide licensing requirement for HMOs occupied by five or more people who form two or more households within blocks of non-purpose built flats.