Sir Elton John and David Furnish are selling their Hollywood apartments.

The couple - who have 15-month-old son Zachary - own two homes in the Sierra Towers building Los Angeles and are selling them for a total price of $5.1 million after purchasing a $7.7 million home in Beverly Hills.

One of the apartments previously featured in Architectural Digest and covers 1,831 square feet and is up for sale at $3.5 million.

The second property adjoins the first but covers 1,151 square feet, with one bedroom and one bathroom.

A potential buyer could splurge on both and have them turned into a luxurious Penthouse apartment in the building - where Cher and Joan Collins also have homes - and enjoy its impressive facilities, which include exercise room, rooftop swimming pool, sauna, doorman, valet parking and concierge services.

Elton and David's new child-friendly home was built in 1966 and boasts three bedrooms, 3.5 bathrooms, a staff bedroom and bathroom, pool, a gym, floor-to-ceiling windows and white-oak flooring.

The move could be because the couple are reportedly planning to have another child after welcoming Zachary via a surrogate on Christmas Day 2010.

A source said: ''The Wheels are in motion. David and Elton have never hidden their desire to extend their family, and believe the time is right for another child.

''By the end of this year, or the beginning of next year, there will be a fourth member of the John-Furnish clan.

''They are incredibly excited and loving every minute of parenthood.''

Speaking previously, David revealed they did not think about which of the pair - who both ''contributed'' to their child's conception - was the father.

He said: ''For the time being we don't have a clue who the biological father is. We look at him every day and at the moment he has Elton's nose and my hands.

''Neither of us care. He's our child. The important thing is that he's healthy and happy and loved.''