For nearly a century, architects have viewed facades with mistrust, going on fear and loathing. This feature, almost universal in all previous architecture, ever, came to be seen as fake and deceitful, as something like the hypocritical morality of the 19th century, and contrary to the modernist ideal of displaying the inner nature of a building on the outside. In the 1960s the architects and theorists Robert Venturi and Denise Scott Brown led a reaction, praising what they called the "decorated shed", but by the 1980s the revived facade was being abused as a postmodern wrapper for bankers' palaces, which seemed to prove that the fear and mistrust had been justified.  The new Roath Lock studios for BBC Wales in Cardiff are, architecturally speaking, almost all facade. There are 250 metres of it, looking across an old dock to the trophies of Cardiff's 25-year efforts at renewal – the Welsh Assembly Building by Rogers Stirk Harbour + Partners, and the Wales Millennium Centre on the site where Zaha Hadid's doomed opera house was once planned. Around the studios is empty space awaiting development under a regeneration plan backed by the Welsh government, and behind is a bit of Cardiff's docks that is still in use for shipping.  The studios are built on the success of Doctor Who and its spin-off Torchwood, just as Cardiff's finest buildings were once founded on coal. The phenomenal popularity of the Time Lord's show, which since its revival in 2005 has been made in Wales, has helped provide the funds and confidence to build a £20m complex where the programme is now made. A corridor in the new building has been named "Russell's Alley", in tribute to the contribution of the Doctor Who executive producer and screenwriter Russell T Davies.  The aim of the new building is to provide ample, well-appointed, highly sustainable production and post-production facilities for the making of Doctor Who, Casualty, Upstairs Downstairs and the BBC's longest running soap opera, the 37-year-old Welsh-language Pobol y Cwm. It means that scattered facilities can be brought together: the downstairs in Upstairs Downstairs, for example, used to be several miles away from the upstairs. Now they are under the same roof.  The complex consists of large sheds interspersed with functional courts and alleys, as in a Hollywood film lot, punctuated with sets of extreme specificity. For Casualty, the mediocre design of a PFI hospital is recreated with uncanny precision, down to the ridiculous public art in the car park. For Pobol y Cwm they have built a chapel front, an estate agent and chippy, and little back gardens with immaculately reconstructed B&Q decking.  Unusual design requirements include corridors wide enough for two Daleks to pass, and a recreation of Holby City hospital's car park in precisely the same orientation as the one in its former location in Bristol. The fear is that meteorologically aware Casualty nerds will bombard the Beeb with complaints if they spot that the shadows are falling in a different way. They also had to make sure that an ambulance could roar into the place without hitting any buildings.  Amid all this stage architecture, what might be called "proper" architecture – as in, designed by architects and written about by architectural critics – doesn't get much of a look in. After all, not even the greatest geniuses in the history of the art, not Palladio nor Wren nor Le Corbusier, have performed spatial magic to match the big-inside-small-outside effect of the Tardis.  Nor is this new building a work of the BBC in Medici mode, as they were in the early days of their expansion of Broadcasting House. It is more like the installation of BBC North at MediaCity in Salford, where a hopefully business-like deal was struck with the developer of a publicly assisted regeneration project. In Cardiff their partner was Igloo, an investment fund dedicated to "socially responsible development", who appointed the architects FAT, whose design seems to have taken the BBC somewhat by surprise.  Chris Patten, chairman of the BBC Trust, said it was like a cross between the Doge's Palace and Ikea, which for Sean Griffiths of FAT is mostly a compliment. His practice is, he says, "the UK leader in decorated sheds", which was what was called for here. Or rather, there was no choice but for it to be a shed, only whether to decorate it or not.  The issue, says Griffiths, was "how do you give any life at all to an immensely long elevation with only one door", which looks onto a quayside awaiting development and currently populated only by some hardy black pines, chosen for their ability to survive salty air. It has to deal with a problem common to incomplete regeneration projects, which is how to suggest life that is not yet there. A laughable hotel across the water, with a frantic roof in the style of Santiago Calatrava, shows how not to do it.  The BBC, moreover, are extremely sensitive about giving away future plotlines and details, and don't want people looking into their studios. The windows to the cafeteria are frosted, in case anyone peers in, sees a new Doctor Who alien having a cup of tea and goes viral with phone-snaps of it. Transparency, a favourite trope of modern architects, is therefore not possible.  FAT, who need little encouragement to come up with such things, have responded with a facade that is mannerist, baroque and "sci-fi retro", which has big cross-shaped windows in reference to Casualty, and gothic octofoils in homage to William Burges, the exuberant Victorian who built his greatest works near here. It is, says Griffiths, "a bit mountain-y" and "a bit wave-y", in response to the local landscape. You can detect the shapes of houses like those in Pobol y Cwm that "morph into space invaders", with a centrepiece that is "Doctor Who goes to Las Vegas" or "baroque mixed with what a cyberman looks like".  The aim is to communicate and engage, to escape constricting notions of good taste and create a "narrative" with which people can connect – and whether you get all the references is not entirely the point, as opposed to getting the sense that someone is talking to you. "Most people don't go into most buildings," says Griffiths. "The facade is what they experience. If you mention the Taj Mahal, what people think of is the facade." He wants to address "the experience when you are there", rather than the "doodle seen from 20,000 feet" that some iconic architects provide. The elevation is designed to work at different scales, with its exaggerated gables speaking to the view from across the dock, while a lower level squiggle addresses the eyeline of passersby.  If FAT can sound flip they are actually serious. They study historic architecture in a way that few other contemporary architects do, and try to learn from, for example, the effects of layering and depth you get in 16th- and 17th-century Italy. They compose and seek complexity. They want to make their shed seem substantial and "tactile", so they give an exaggerated thickness to its facade.  That the results are not precisely like those of Florence or Rome is due to the ferocious constraints of time and money under which buildings are now built, and the contracts that limit the architect's role to specific areas. FAT would have liked to spread their influence deeper into the building – to the somewhat basic reception and cafeteria areas, for example – but it was not possible. "Computers and Excel spreadsheets make the world," says Griffiths, "and it's a strange assumption to think that architects have any power to change it." FAT's attitude is rather to make the best of what they've got.  Making the best of it in this case leads to a facade where their escape from good taste has been achieved with exceptional success, but which might fairly be described as stonking. It is bold, engaging, rich, entertaining and complex. It commands its tough site and helps you forget that this zone is still largely wasteland. It achieves something beyond the abilities of many current architects, which is to make a very big facade. Of all the BBC's recent adventures in architectural patronage it is, by accident, one of the most successful.
The new BBC Wales studios are all about front – as well as Doctor Who, writes Rowan Moore