It's London's greenest building since it opened two years ago, but now the Upper Thames River Conservation Authority (UTRCA) headquarters has picked up international recognition.

The Watershed Centre building was ranked second in the world for its energy efficient design.

"On a 30 below day the building is performing optimally today. This is where it shows its colours in terms of sustainability and energy efficiency," says architect Randy Wilson.

The facility has an Energy Star rating of 98 out of 100.

The mounting awards has builders and architects from around the world requesting tours.

"They marvel at the layout of the building, the energy efficiency of the building, the design. And certainly most of them would like a spot to work in here," says Alex Shivas with UTRCA facilities.

The building cost roughly $12 million to build.

If the green features of the building are removed, the price would drops by about 15 per cent.

But the UTRCA expects to reclaim that amount of money back within three years through energy savings.