Welsh Slate roofing slates have played a “critical” role in the award-winning renovation of one of London’s most unusual buildings.
A two-year conservation project to restore the roofs, and 80 decorative dragons, on the 18th Century Great Pagoda in the World Heritage Site of the Royal Botanic Gardens at Kew will give the public access to the upper floors for the first time in decades.
The 10-storey building was one of the jewels in the crown of Georgian London, one so unusual that a suspicious public were unconvinced it would remain standing when it was built in 1762.
The brightly coloured dragons had been absent for more than 200 years after they were removed in 1784 when slate and copper work replaced earlier experimental cast iron tiles on the building’s roofs under the direction of the original architect Sir William Chambers. It was rumoured they were removed to be sold to settle George IV’s gambling debts but experts believe they had simply rotted over time.
The roofs on nine of the storeys (each one of which was unique) of the Grade 1 listed building were then laid with Cornish slate and sheet copper cappings on the hips, while the top cupola roof was entirely covered with sheet copper.
While the roofs have now been re-laid with Welsh Slate’s Cwt-y-Bugail slates (600mm x 300mm on the ground floor and 500mm x 300mm on the upper floors), 72 of the old wooden dragons have been replaced with 3D printed nylon replicas (the other eight were hand-carved in wood) fixed to stainless steel brackets for extra weather security.
The cost of the conservation work – £5 million – was paid for by the charity Historic Royal Palaces whose objective was to return the building as closely as possible to its original appearance using newly-discovered historic documents and archaeological analysis.
That aim guided many of the decisions made, from the use of traditional materials to the setting out of the dragons and the final colour scheme, under the expert guidance of conservation architects and frequent Welsh Slate specifiers Austin Smith Lord.
The Welsh slates were laid with copper nails to the original close boarding on pitches ranging from 20° to 45° for main contractor Blue Sky Building by sub-contractor Richardson Roofing who are specialists in heritage roofing and who won a 2019 Roofing Award for the project. Slates to the hip abutments were hand cut and at ground floor, the roof sweeps upwards which was achieved by curving the sarking boards below the slates, all this through an extreme winter.
Directly above the slated roof on each level is a flat copper roof which can be accessed through glazed doors on each floor. These roofs acted as viewing balconies and were surrounded by wooden balustrades.
As part of the restoration, Richardson Roofing was contracted to strip off and renew all slate and sheet copper weatherings but during the erection of scaffold and as closer inspection became possible, Historic Royal Palaces, along with Historic England, became more interested in retaining a proportion of the copper sheet weatherings. While there were signs of wear, the copper to the flat roofs and cupola were not deemed to be in need of immediate repair and were retained.
Prior to the work being started, Richardson Roofing and Austin Smith Lord designed a mock-up of a typical hip section upon which the dragons would be located. A full-size mock-up was built at Hampton Court Palace and various copper and slate details were tried. Then, as the start of work neared, the mock-up was relocated to Kew Gardens where a temporary roof was erected to enable further changes and experimentation.
An architectural requirement for the dragons was that they should appear to be standing on the roof coverings and as such the brackets had to be low enough for this to happen. To achieve the low profile, each bracket was sunk inside the dragon with copper sheet sleeves soldered to each hip capping. The hip cappings in turn were welded into sheet copper soakers located between each course of slates.
Conor Richardson, business development consultant for Richardson Roofing, said: “While the restoration was headed up by the architect, many other parties including Historic Royal Palaces, Historic England and Kew Gardens themselves, not to mention Richmond Upon Thames building department and the main contractor, each had an input into how the works proceeded.
“Dealing with so many different authorities raised challenges we had not previously encountered but after agreeing to work longer hours and employing additional hard metal and slating labour the project was completed on time.”
Because of the high level of interest in the project, Historic Royal Palaces also approached Richardson Roofing to help run a building conservation masterclass as part of the charity’s partnership with SPAB (the Society for the Protection of Ancient Buildings).
With help from Welsh Slate, Richardson Roofing delivered an enthusiastically-received slating masterclass attended by architects from all over the country. Some even got hands-on with the slate cutting demonstration!
The Great Pagoda was designed for the royal family by Chambers who was inspired by the buildings he saw when working in Canton and his designs for the Kew monolith were influenced by prints he had seen of the famous porcelain pagoda at Nanjing.
Built in the Chinoiserie style, Londoners and tourists alike flocked to see the striking 50m tall structure which formed part of a homage to the Grand Tour in the royal garden.
Although it had suffered much in the centuries since – losing original colour, materials and meaning – it remained the supreme example of Chinese style in Europe. Now, after years of investigation and research, the building has been repaired, conserved and returned to its former glory.
It was formally opened by HRH The Prince of Wales in July 2018.
To watch a video of the project, please go to https://www.richardson-roofing.com/portfolio/kew-pagoda-2/
Austin Smith Lord director and conservation-accredited David Millar said: “For the replacement slates, we tried hard to use the same Cornish slate. The original quarry was closed and the nearest existing quarry had already committed to using its entire annual output to a local housing development. We tried another Cornish slate but the thickness and quality was different to the original slate. We eventually chose Cwt-y-Bugail slate which is a close petrological match and has the same consistency as the original slates.
“The Welsh Slate was critical to the aesthetic appeal of the roof areas against the 1762 paint colours but as well as being excellent aesthetically it also meets the performance requirements.”