The space above the UNESCO World Heritage-listed Hyde Park Barracks has been sold for $20 million.

Three different developers, including Lendlease, are said to have purchased “air rights” to the space for between $1,460 and $1,610 per square metre. This is the first case in which an Australian UNESCO-listed building has sold its air rights, and the second case for a government building in Sydney.

The money City of Sydney receives from the sale will be earmarked for the conservation of a range of heritage buildings, while developers will have access to space that would have otherwise been off the market.

The sale will allow Sydney Living Museums to improve visitors’ experience at the Barracks, which are currently closed for renovation, re-opening in December this year.

In a comment to the Sydney Morning Herald, NSW minister for the arts and heritage, Don Harwin, has referred to the scheme as “an innovative way for our metro-based cultural institutions to raise new investment that ensures the continued conservation of our heritage sites”.

However, NSW Greens’ David Shoebridge has countered this, arguing that the scheme in encouraging overdevelopment in Sydney.

“The 12,000 square metres of development yield that’s sold from [the Barracks] is going to turn up somewhere else in Sydney,” he says in a comment to the ABC.