Part Egyptian tomb, part masonic temple, the 1930s headquarters of the Royal Institute of British Architects has always exuded a cultish air. Sited on London’s illustrious Portland Place, among embassies, consulates and oligarchs’ pieds-à-terre, it is a fittingly regal headquarters for a chartered profession that has long styled itself as an exclusive gentlemen’s club. If you have ever been to an event there, you probably won’t have paid much attention to the dull brown mural at the back of the auditorium. It’s a dirty, poorly lit and badly scuffed screen, which tends to fade into the background of the surrounding art deco pomp. And there’s a good reason that the RIBA hasn’t wanted to you look at it too closely. “It’s one of the most racist things I’ve ever seen in my life,” says Thandi Loewenson, a Zimbabwe-born architectural designer and researcher. “And that’s saying something.” Take a look, and you’ll see groups of semi-naked figures from all corners of the British empire, cartoonishly depicted as primitive savages with exaggerated features, huddled in timid submission around the edges of the mural. In the centre, radiating above a map of Britain like some heavenly vision, is the RIBA council, depicted as a professional parliament of identical faceless figures. Floating between the professionals and the natives, in a kind of architectural halo, are the symbolic buildings of empire: the government buildings of Pretoria, the viceroy’s palace in New Delhi, the old parliament house of Canberra, and other works authored by the institute’s distinguished members. “It’s a very useful document,” says Loewenson. “It celebrates the role of the architect within the structures of colonialism. The buildings depicted here are literal repositories of stolen land and exploited labour.” But, in her eyes, there is something crucial missing from the tableau. “What’s absent are the sites of material extraction themselves – the mines, farms, plantations and jails, from where all of this wealth was violently taken.” So she has come up with a solution. Along with several other designers from the colonial diaspora, Loewenson has been commissioned as part of a new exhibition, Raising the Roof, curated by Margaret Cubbage, which aims to shine a spotlight on the colonial symbolism embedded throughout the RIBA building – and propose ways that these histories might be interpreted and untangled. Loewenson’s response is a startling mural of her own: a shimmering drawing etched into panels of graphite, conceived as “another layer” to be superimposed on the problematic Jarvis mural in the auditorium. Her image, created in collaboration with Chinese designer Zhongshan Zou, is a reinterpretation of a 1921 drawing of a lead and zinc mine in Kabwe, Zambia, called Broken Hill. It was one of the first sites of British colonial mineral extraction and it’s now one of the most toxic places on the planet. As a result of decades of mining, 95% of the local population have elevated levels of lead in their blood, leading to lifelong health conditions. Last year, the UN’s special rapporteur on human rights described Kabwe as one of the world’s “sacrifice zones”, where corporate environmental contamination has created shadowlands of misery. Loewenson’s speculative proposal would see the mural daubed with layers of graphite – “this messy, slippery mineral, extracted from the earth” – so that fragments of the old world order, depicted beneath, would glimmer though the image of the toxic landscape that it created. “Traces of the original mural can still be seen,” she writes in an accompanying text. “The ghosts of buildings glow through the image, now contextualised by slag heaps and accompanied by the much less glamorous infrastructure of extraction that supported their own construction.” She won’t, sadly, be let loose on the mural itself, in this Grade II*-listed building, but it is a provocative proposition. Built in 1934, to the designs of George Grey Wornum, the RIBA was conceived as a monument of imperial splendour. It was designed as a showcase of colonial riches, featuring African marble on its processional staircase, Indian silver grey wood on the floors of its halls, and Australian walnut and Canadian maple on the walls of its council chamber. In the building’s Florence Hall upstairs, the rear wall is lined with a carved wooden screen that stands as a hymn to the raw materials of the imperial dominions – a stately billboard advertising exotic things that architects could specify in their projects. One panel depicts a South African mine, while another shows a Canadian lumberjack hacking down a pine tree, of which the screen itself is made. Architect and designer Giles Tettey Nartey, who grew up in Ghana, has responded to the panels with a series of beautiful, organically shaped stools, carved from the same Quebec pine as the screen, but stained a dark, inky black. They are arranged like little islands around a meandering table, where a blank tablet is fixed in the centre, awaiting a future interpretation panel. “I didn’t want to impose a literal alternative to the Dominion Screen,” says Tettey Nartey, “but instead create something that would help to facilitate multiple conversations. I want people to pull up a stool, discuss, and come up with a collective response to the screen.” He says the 17 stools represent the countries “left out” of the carved panels (which feature Australia, South Africa, India, Canada and New Zealand), making us think about “other places that also had the British ideal of architecture imposed upon them”. Hanging on the wall nearby, India-born architectural designer and artist, Arinjoy Sen, has come up with a dazzling, psychedelic alternative to the Jarvis Mural. He thrusts the Indigenous subjects of the empire centre stage, transforming them from suppressed savages in the margins to active players in a colourful carnival of creativity. Flanked by trees of Burma teak and west African mahogany, his drawing unfolds as a riotous, intricately detailed scene that samples numerous details from around the building to form a kaleidoscopic spectacle, shining with sunny optimism. The RIBA should commission a full-size version of it at once (preferably embroidered, like Sen’s delightful contribution to last year’s Venice Biennale) to replace its drab, racist mural downstairs. Finally, artist and writer Esi Eshun contributes a poetic film that combines archival images with her own thoughtful commentary as she wanders through the building. She examines a number of the colonial structures depicted in the contentious mural and unpicks their histories, in relation to the native peoples on whom these buildings were “at once imposed and denied”. The retractable screen is a “cartography of desire and despair”, she says, which, as it rises out of and lowers back into the floor, evokes “imperial cuts and continuities, partitions and enclosures”. The timing of the exhibition couldn’t be more apt. It opens in the week that Lesley Lokko receives the RIBA gold medal – the first Black woman to be awarded the hallowed gong – and at a time when the institute has its youngest and first ever Black president at the helm, Nigeria-born Muyiwa Oki. It is a moment of reckoning for the 190-year-old institution. This year also marks the 90th anniversary of the building’s completion, which sees the launch of RIBA’s capital project to refurbish and restore it, for which this exhibition will hopefully provide useful food for thought. “This is not just an exercise in institutional self-flagellation,” says architectural historian and head of the London School of Architecture, Neal Shasore, who is advising on the conservation management plan. His research into the history of the RIBA building led the institute to add interpretation panels to some of these problematic features, and it also inspired the origins of the new exhibition. “These commissions are serious, nuanced responses to the complexity of the building’s colonial entanglements.” He would ultimately like to see the “egregiously racist” Jarvis Mural taken down, acceded into the RIBA’s collection to be displayed contextually, and replaced with a new commission. “It’s not about pretending it wasn’t there, or ‘cancelling’, or any of these boring discursive tropes,” he says. “You can make it more present, and find imaginative ways of rewriting some of those problematic narratives, completely transparently. This is not a process of erasure.” Barely anyone had noticed these elements in the building before, he argues, and this is an opportunity to highlight them, as well as open up the wider conversation. “From the Confederate monuments in the US, to the Rhodes Must Fall campaign, to the Colston moment in Bristol, we’re finally seeing these aspects of our built environment, and reflecting much more fundamentally on what the nature of architecture is – and the ways it can sometimes be co-opted for nefarious ends.” Raise the Roof: Building for Change is at RIBA, London from 27 April to 21 September