Shopping CentresWhile some stores have rightly preserved their historic elevations, Roches has stripped off completely, paring itself back to the basics and starting again, writes Emma Cullinan

Some say that shopping is the new religion. If that's the case then department stores are the cathedrals.

While we may expect luxury from Brown Thomas we'd grown used to cosy old department stores, whose internal decoration hadn't quite stood the test of time. But Dublin stores have been on a spending spree.

Clerys and Boyers have had makeovers, and now Roches Stores on Henry Street has come steaming in with a stunning new façade and a swanky interior. While stores, such as Clerys, have rightly preserved their historic elevations, Roches has stripped off completely, paring itself back to the basics and starting again.

The more traditional customers almost stagger around wondering if they've come to the right place. It's as if an old, grey haired, tweed-wearing friend has turned up with expensive highlights, Jimmy Choo boots and a Giorgio Armani suit, cut well above the knee.

A huge slab of white Techcrete spans the front of the building demonstrating that this store has broken with convention. It looks more like the type of shop front you'd find in Munich.

Dublin has a fine tradition of consistent street scapes. Our Georgian terraces are stunning. But sometimes what lies behind is a lie, when it comes to commercial buildings. While a department store is a single, albeit divided, entity to the front many of them are divided on a vertical scale to create a sense of a row of houses or shops.

But Roches has turned this idea around and gone horizontal. "We've been honest about the function of the building," says architect Tom Mulligan of Newenham Mulligan and Associates (NMA). The design follows customer needs and expresses what the building is used for.

While department stores are single entities their innards are disparate, in Roches case these now comprise trendy new concessions such as Zara, Hard Candy and Mad Dogs. The white slab on the front elevation draws the whole building together, pronouncing its unity.

Inside the architects had to contend with a split building with mismatched floors. Designed in the 1950s by the same firm of architects (NMA), half of the store was built in the 1960s and the other half in the 1970s. The 1960s gable wall became a spine up the middle of the store when the 1970s addition arrived. This cut Roches in half, as those who passed from the former toy section into electrics in the basement will remember.

Retailers are now savvy about what they call customer circulation and this new building is easier to negotiate. The spine wall has gone to be replaced by four sturdy columns. A 10m wide, impressive atrium has been added at this central point which serves as a location point for customers, not least because this is where the escalators are.

The entrance doors have all been enlarged. The central doors have been widened, and the corner entrances have been taken up to ceiling height (the east-facing entrance no longer leads straight to the basement). The external doors drop down into the pavement so, when the weather's good, the entrances will be barrier-free.

One detail that might impede customer throughput, or bunch people together, is the elongated barrier at the end of each escalator - but this is apparently for safety reasons. If there is a crush no one will find themselves hauled along by the escalator belt. The new glass canopy along the street has replaced the concrete one. This brings the huge building down to a human scale and presents the shop's window to potential buyers. But there is also something spectacular to draw the eyes up the building.

The Chocolate Soup cafe cantilevers out from the front wall. Coffee has now become our drug of choice and if it can be drunk it in special surroundings then how much better the experience. This small, slender cafe, with bistro tables and chairs, plus cosy booths, has a glass floor and wall so diners can engage in people watching and also perhaps get a sense of the David Blaine experience. Those looking up from Henry Street see feet padding around on the glass. If you don't get a kick from your coffee, then there'll be a frisson of excitement as you walk on the glass floor (31.5mm thick and stronger than concrete, the architect assures us).

In keeping with trends, there's a juice bar too, with a striking red wall and a suspended curved ceiling above it. You will be able to eat and drink on an upper terrace, opening in spring. "When you're shopping, it's always lovely to stop for a while and get outside," says Tom, something continentals know from experience. The view from here shows just how poorly parts of Dublin have been put together. The roofscapes around this area are a jungle of weed-strewn flat roofs behind parapets, air conditioning systems and pigeon barriers plus ill-assorted gaps between buildings. How different to the view of the Parisian roofscape from the Eiffel Tower. The impressive conversion of Roches has been carried out beneath a weight of restrictions. Site access was difficult, and required special permission to open up the pedestrianised street at night.

Much of this work was carried out in the small hours because, amazingly, the store stayed open throughout the project which has been on site for two years, even when the spine wall was dismantled. Roches just closed for two days recently to test services, such as the sprinkler system. Working with the mismatched floor heights the project director, partner Michael Byron, took the opportunity to house the services in a false floor between two existing floors. The firm is keenly aware of natural daylight and ventilation but many stores demand even temperatures. They have compromised, they say, and have tried to be economic.

It does seem a strange choice to enclose a building in solid slabs, at a time when many are discovering the joys of incorporating as much natural light as possible. But this has been addressed with a clear glass roof above the atrium and the glass front corners of the building, supported by steel spiders internally.

And the elongated floating slab, designed to make the building look longer, does make for an impressive addition to the overall composition. The black Rustenberg stone at the base, the glass corners, white block, glass box cafe and the black overhang designed to define the top of the building, work well together.

Inside the space looks smarter but department store innards are pretty similar worldwide. Yet the architects have worked to improve the space within such a restricted design opportunity: there is a higher percentage of accent lighting - with directional ceiling lamps to highlight various merchandise - and where ceilings are low, in the "funky floor" of women's clothing, they've highlighted the beam structure. They've also created five retail floors where there were formerly three (the rest used to house stock and staff who will soon move to an extension over the Ilac Centre).

The white slab won't please everyone, but this building has dared to be different and, as ever, architects need clients on board to realise such designs. "The client was excellent," says Tom, attesting to the bravery of Roches. "Unless your client shares your vision, you can't move forward."