The Honolulu City Council unanimously approved a special management area use permit for expanding the former Kaiser Estate in East Oahu’s Portlock neighborhood on Wednesday.

The 9-0 vote allows the owners of the 5.4-acre property, Annie and Fred Chan of Evershine II LP, to add a third single-family mansion to the oceanfront estate and make other additions and improvements valued at $16 million.

Work is expected to last 18 months.

The major addition will be a new two-story residence with 20,000 square feet of living space, a guest wing, a cabana and a pool.

An existing 14,000-square-foot residence originally created mainly for boat storage will be renovated along with an adjacent staff house to which would be added a four-car garage and a pool.

One other big piece of the project is renovating the existing 12,350-square-foot main house and adding a new four-car garage topped by a guest/staff house.

Special management area use permits address potential negative impacts on shoreline areas and are required for renovation or construction of homes with more than 7,500 square feet of living space.