Kew Gardens in London has completed the largest restoration project in its entire history: a redevelopment of its iconic Temperate House, now home to 10,000 plants, including some of the world’s rarest.

The long and painstaking repair of the historic glasshouse, overseen by Donald Insall Associates and costing £41m (€46m, US$54m), saw 400 staff and contractors remove 69,000 individual elements from the building to be cleaned, repaired or replaced. The structure’s intricate ironwork and ground paving was carefully repaired and thousands of panes of glass replaced.

The Temperate House – show-house of the Gardens’ largest plants – was designed by architect Decimus Burton and opened to the public in 1863. Over the following 40 years, north and south wings – called the Himalaya House and the Mexican House – were added when finances allowed.

Reflecting the design trends of the era, the building featured a rich mix of decorative motifs, including intricate stone urns and statues, and was admired for its collection of plants and architectural details.

However, during the Second World War the glasshouse suffered indirect structural damage, causing leaks and corrosion that persisted despite repairs. A first restoration was completed in 1980, but by 2011 the government warned that repairs were required within three years. The attraction was closed in August 2013 and covered in scaffolding, hoarding, and a tent-like structure large enough to cover three Boeing 747s.

Over the following five years, the building has been carefully restored to its original design, albeit using new 21st-century materials. As the plants inside had outgrown the space, blocking sunlight from reaching the ground, they were removed and propagated by Kew’s gardeners throughout the restoration period, with the species now reintroduced – creating an “architectural wonder, a horticulturists’ haven and the most captivating of classrooms.”

Famed naturalist and broadcaster Sir David Attenborough re-opened the Temperate House on 5 May.

“The restoration of the Temperate House has been a complex and immensely rewarding project, recalibrating contemporary understanding of Victorian architecture and the development of past innovations,” said Aimée Felton, lead architect on the project. “New glazing, mechanical ventilation systems, path and bedding arrangements all took their founding principles from Decimus Burton’s own drawings, held within Kew’s archives.”

Richard Barley, director of horticulture at RBG Kew, added: “It’s been amazing watching this project unfold, the building emerge gloriously and some of the world’s rarest plants safely reach their home. This is world class horticulture, science and design working together to create something truly impressive.

“The Temperate House is a glistening cathedral where the new glass allows the sun to stream in and the ironwork has been restored to its glossy best. And I’m most excited that it is for everyone, from young to old, for budding gardeners or aspiring artists, for those making a pilgrimage from great distances, and for our local community, we hope every visitor will see plants in a new light”.

Speaking to the BBC, Attenborough said: “It’s a breathtakingly beautiful space. These plants are wonderful, and here they are, safe from peril.

“Kew does all sorts of things that nowhere else does. If you want to identify something, this is the ultimate authority worldwide. It’s the most important botanical institute in the world and occupies a very special place in the science of Botany.

“In some circumstances, the only way you can prove that a particular species is that species, is to come to Kew and compare what you have with what is here. This is why people come from all over the world to the Kew Herbarium, and to these great glasshouses.”

The Heritage Lottery Fund awarded around £15m (US$20.2m, €17m) to the project, with around £10m (US$13.5m, €11.3m) from the UK Department for Environment, Food & Rural Affairs, and £8m from private donations.