Wit in architecture is tough to pull off. Architecture clashes uneasily with rat-a-tat oneliners. By the time a “witty” building is complete, its in-built epigrams, so clever on the drawing board, can make you squirm.

There’s humour aplenty in Baroque, Regency or Victorian architecture, though the gentle, intellectual jokes would hardly split sides at a librarians’ convention, let alone Jongleurs. Wit, too, came back in a big way with 1970s postmodernism, with architects hogging the stage with their humorous asides on historicism. But Woody Allen wasn’t quaking.

Fashion Architecture Taste (Fat) do wit, big time. I’m sure they get bored stiff being called architectural pranksters, but then they’ve only themselves to blame. Charles Holland, Sean Griffiths and Sam Jacob — bright chaps who left university just in time for the 1990s building slump — needed something to twiddle thumbs with, so they called themselves an art-architecture collective, peppered the installation and public-art scene with irony-loaded stunts and professed a passion for the love that dare not speak its name — 1970s postmodernism. This was like admitting that you thought Cannon and Ball underrated.

Still, they careered around, being outrageous, dissing Corbusier and Conran in favour of architecture with knobs on. One pavilion shimmered in sequins like a disco diva. Their 1999 exhibition Kill the Modernist Within trumpeted 1930s Tudorbethan. They covered bus shelters in thatched roofs.

Their Big Serious Point, learnt, naturally, from the now unfashionable 1970s postmodernists Robert Venturi and Denise Scott Brown, is that overfunctionalist, po-faced modernism has stripped architecture of meaning, history, fun and joie de vivre. God knows how they kept going, but they made it through the hard times, and at last they have found someone who’ll take their serious fun seriously.

You can’t miss Woodward Place. There are few terraced houses in Manchester with slap on like this: one long, defiantly stage-set brick façade, doubling back on itself and looking like a cardboard cut-out from The Simpsons, coloured in bright polychrome brick and topped with Dutch gables. You can’t help smiling.

There is depth to the depthlessness. Focus hard on the diagonal brickwork and you’ll see ballooned-up arts and crafts patterning. There’s more William Morris in the hearts and crosses carved into the distinctly DIY balconies. This social housing replaces a previous attempt to cosy-up modernism, the Cardroom estate’s 1970s suburban brick boxes. They were loved by most tenants, but badly planned, isolated and blighted with deprivation. The quarter is now being ambitiously rebuilt with an eclectic mix of architects by the developer Urban Splash as one of the Government’s millennium communities.

Urban Splash has to square the sociological circle of improving the lot of the existing locals while giving this scrap of inner-city Manchester a viable future by attracting the more affluent. The first step is to rehouse the much-abused locals in homes a little denser — to make room for the new lot — though as spacious and of better quality, and not to annoy them with fancy architecty ideas about good taste. Step forward Fat, the very last architects in the world to impose wood floors and middle-class taste on anyone. Their pop-culture love of crazy paving and knick-knacks is at least heartfelt. The tenants voted 99 per cent for their design.

Behind a showy façade is a plain shell in the shape of a (modern?) box — a functional device, but also an intellectual one. This is definitely a decorated shed, which Venturi and Scott Brown presciently foresaw as architecture’s future three decades ago. But it’s a spacious shed, high-ceilinged, humanely detailed (no PVC windows) and well planned, with the kind of homely elements (bay windows, nooks that serve no purpose) usually edited out by Scrooge-like housing association book-keepers.

Fat do wit well, though enough is definitely as good as a feast. Praise be, few other architects have the stomach for it, let alone 1970s po-mo. Fat’s tardy emergence, though, does point towards this season’s big architectural trend, decoration. Herzog & De Meuron are at it, Rem Koolhaas is at it. Steel and glass are out. So unsustainable. So 1996. Even the arch-monochromist Lord Foster’s been spotted wearing a jaunty salmon-pink suit. It’s a slippery slope to flock wallpaper.

Fat’s exhibition In a Lonely Place is at the Royal Institute of British Architects, W1 (020-7580 5533), until May 2, 2006