Roger Stirk Harbour + Partners’ have completed their £135m (US$231m, €170m) extension to the British Museum, London.

As one of the most popular visitor attractions in the world, the British Museum is a defining institution and its new World Conservation and Exhibition Centre has been a long time coming.

Rogers Stirk Harbour + Partners (RSHP) won the contract for the extension in 2009 from a shortlist of top architectural practices, such as David Chipperfield.

The initial master plan for the site was rejected in early 2006, RSHP and the British Museum collaborated closely with Camden Council as well as English Heritage and CABE to ensure that the the second master plan fitted everyone’s brief and was approved in 2009.

Following the opening of the first phase of the development – a temporary exhibition space that opened in March – the final phase of the extension is soon to be up and running as it is now complete.

The 17,000 sq m (55,774 sq ft) site now features state of the art laboratories and studios, conservation studios, copious amounts of storage for the museums ever growing collection - as well as temporary collections - and a Special Exhibitions gallery. A large portion of the development is subterranean, meaning specialised equipment can be onsite, whilst providing three underground floors of storage space.

Crafted of cast glass over a steel frame with a stone facade, the new building is yet another phase in the British Museums evolution, since its opening in 1759 to the modern day.