Sydney's central business district rents will plunge by 7.5% this year and will not recover for at least two years, according to new client research from Jones Lang LaSalle.

While average net effective rents are expected to climb to about $610 per sq m by 2015, market commentators say the cost of building a Sydney office tower in a prime location is $800 per square metre.

Currently, Sydney has four office towers under construction, including 420 George Street, 85 Castlereagh Street, Darling Walk and 1 Bligh Street.

A research report on Sydney office rents by Jones Lang Lasalle, sent out to subscribers, shows rents will not increase until 2015 in Sydney's city.

The Australian