Major preservation works are underway to replace the tilted glass skylights that define Stirling and Gowan's iconic Engineering Building at the University of Leicester, England.

The "once in a lifetime" £19.5 million project will see each of 2,500 panels that form the Engineering Building's distinctive sculptural roof structure and facade replaced, with the aim of extending the building's use for a further 50 years.

Considered one of the forerunners of Postmodern architecture in the UK, the factory-like building was designed by British architects James Stirling and James Gowan in 1957 to house the University of Leicester's engineering department.

Stirling and Gowan set the building's glass roof panels at a 45-degree angle, creating rows of diamond-shaped skylights that bring light into the engineering research laboratories from the north. But the lifespan of this glass roof has now come to an end.

The 2,500 roof panels, as well as those that form the glazed facade, will be now be replaced.

"This is a once in a lifetime project," said project manager Pete Bale.

"It is very exciting that we are travelling the road that Stirling and Gowan trod all those years ago, in that we are producing the solution to an inspirational concept design, to modern performance and health and safety requirements, that has never been done before."

Part of the new glass roof will rest on the original windowless brick base, which also features brick-covered doors, while the other section of the roof will sit atop the updated glass facade.

University of Leicester is working with English Heritage, conservation campaign group Twentieth Century Society, engineers Arup and the local authority on the project, which is expected to extend the building's functionality for a further 50 years.

Fabric-wrapped scaffolding and a tensile netting under the roof line will weatherproof the building and allow the workshops to remain occupied throughout the refurbishment works.

The building completed in 1963, the year Stirling and Gowan parted in a professional capacity, and it was granted a Grade II* heritage listing in 2003.

"The design has generated much controversy and architects come from all over the world to see it," said the school's head of engineering department professor Helen Atkinson. "It has even featured on a postage stamp. We are proud to be educating engineers for the 21st century in this iconic building."

Stirling – who gives his name to the prestigious architecture award the Stirling Prize – also designed the one of the movement's most recognisable buildings, No 1 Poultry. James Gowan, who died earlier this year, was responsible for the RCA's flamboyant yolk-coloured bookshop.

The £19.5 million needed to complete the renovation is partly funded by a loan from the European Investment Bank and partly from the University's own capital.

Work is currently underway and is expected to complete by the end of 2016.

Photography is courtesy of Mott MacDonald Façade Engineering and the University of Leicester.