Jones Lang LaSalle has sold Skyline Central 2 in Manchester on behalf of Wheatley Properties to an undisclosed buyer.
The property was marketed with a guide price of £20m.
The 129-unit block is located within a 10 minute walk of the city centre.
Tom Henry, residential director in the Private Rented Sector team at Jones Lang LaSalle, said: "The sale of Skyline Central 2 illustrates that as we predicted, demand for PRS stock in the regions is growing due to the higher income returns and increasingly positive prospects for capital growth.
"The building is the largest of its kind in the market and we expect to see more developments of this nature coming to fruition as interest in the build to rent sector continues to grow."