A Dublin architects' firm bought a car-park and turned its mews building in a Georgian lane off Fitzwilliam Square into a light-filled open-plan office and four apartments. Emma Cullinan reports

Anyone seeking new clients will usually show them a portfolio but in the case of Newenham Mulligan and Associates (NMA), prospective clients who visit the architects' offices will be sitting in an example of the firm's work.

The practice had been in Baggot Court, Dublin, for nearly two decades, tucked in behind Dublin's Georgian façade in a former paper warehouse. In the past these backlands, in this case to the rear of Fitzwilliam Square, would have been teeming with activity generated by tradespeople and horses. This mews laneway is still a kind of transport hub, only now the area is full of car-parks attached to the rear of Georgian office buildings jammed with 21st century commuter traffic.

A few years ago NMA bought the car-park beside its office with a view to creating a mixed-use building. "It used to be dead here in the evenings and even during the day we felt lonely," says architect Tom Mulligan.

So when it came to upgrading, brightening and increasing the size of its existing offices, the architects added on four apartments next door. Meetings with Dublin City Council concluded that such a mixed-use building would help to revitalise this city centre site.

The resulting building re-establishes the streetline of the past in its positioning and massing but isn't in itself a pastiche of former styles. Instead it's a contemporary, multi-layered structure whose various elements are competently drawn together.

The architects looked at former maps of the area and the new building addresses the street in much the same way as previous buildings did - even if they were houses for horses.

In current urban planning parlance, the former car-park was causing 'leakage' at the corner where a coach-house used to stand. Part of the task, then, was to remake this corner with a new building.

Essentially creating a complete terrace on their own, the architects discussed whether the building should be a single edifice or broken up. They opted for the latter and so the question was how to break up the façade and articulate the street. The design involved many discussions, as would be expected when a group of architects creates an office for themselves.

Then the job had to be juggled in with work for clients, which took priority: it's a running joke that many architects live in half-finished homes as they spend so much time working on other people's properties. "There were lots of design reviews and model making," says director Michael Grace. The result is a dynamic mix of shapes with everything in place for a reason, whether that be functional, aesthetic or psychologically pleasing.

Rather than breaking the scheme up completely, and pretending that this is a street made up of different buildings, the same materials (steel, glass, white render and timber) are used throughout the building in various configurations so that areas are differentiated but linked. Iroko slats cantilever off the façade as window frames and balconies, yet elsewhere the timber is recessed, as window panels, a garage door, and stairwell cladding.

On the façade, timber plunges down through the white render, and on to the ground via the stone wall at the base. This continuous wall of Donegal limestone visually ties the whole building together.

Between the four apartments on the left and the office on the right is a glass box housing the reception at ground level, topped by a roof terrace. This central area works as a light-well and, along with the ample glass on the street fronts, lets the building take care of its own natural lighting needs rather than worrying about shadowing from neighbouring structures. The central area also provides one of the many links through the building. A staircase runs from here right up through the first floor to the upper office floor with views back down and across to the apartment stairs. Those ascending and descending can to see their clambering counterparts in the apartment building opposite.

The apartments were built first so the architects could work in that building, while the open-plan office was being constructed. Any doubts about the benefits of open plan were dispelled when staff were cramped into 'apartments'."There is a psychological barrier to going into someone's room," says Michael, "whereas in an open-plan office you can just walk up to someone's desk." This is a company that encourages interaction and the design enables that.

The new office comprises open-plan first and second floors and a ground floor of meeting rooms divided by glass. There's also a shower on the other side of reception for glowing cyclists who represent hope for the future now that the number of car-parking spaces has diminished (the car park is beneath the apartments).

The break-out spaces, such as the terrace and bridge above it, must be a boon for those who work on the top floor, where the ceiling height is comparatively low. The Kalzip-coated roof - which looks like an iconic 1960s coffee table - wasn't just an architectural whim, it was created to make the most of planning restrictions. The architects were not allowed to build above the ridge line of the former pitched roof building and this space, which slopes away from the apex, was the solution.

Staff now work facing outwards and there are plenty of routes to the outside world: both actually and visually, including down the stairs to the ground floor, out of the banded windows to the street and onto the bridge between the two parts of the building, which has become a popular lunch location.

So the curved roof serves a practical function as do the two protruding iroko boxes on the facade, which subtly mark the entrance to the building, leading to that double-height glass space which offers a grand entrance with a light touch.

The outside of the building looks intriguing, with all of its elements brought calmly together with a restricted palette of materials and the mirroring of certain proportions of neighbouring elements. The unmatched curved form works because it sits above everything else although its glass wall reflects the glass across the connecting terrace. This acts as both a divider and a link between the living and working parts of the building.

This development could have been a vast, blank box taking up a whole terrace, for which there are plenty of precedents - after all this is just a hidden laneway. Yet this building shows just how these forgotten, car- and grotty shed-filled spaces in prime city-centre locations, can be turned into vibrant, well-designed living and working hubs.