YORK STREET flats were the last real slums in Dublin to survive into the 21st century, and probably provided a setting for films that needed an authentic "tenement" backdrop. But now they've been replaced by a superb social housing scheme that would put even the most "exclusive" private sector apartments to shame.

"The old flats were really appalling," says architect Seán Harrington, whose firm designed the replacement housing.

A Georgian terrace, rebuilt in 1949, the block contained 99 apartments, 45 of which faced northwards onto the street and the rest faced south, looking out over bleak concrete yards with washing lines.

Harrington is a committed architect who is passionate about housing. His "learning curve" in this area was a competition, sponsored by Dublin City Council, for an affordable housing scheme on Holles Street; a complex public-private partnership (PPP) project, it is only now nearing completion six long years later.

"When we came on the scene in York Street, the city council had already decided to demolish the flats," he recalls. "We said we wanted to meet the remaining residents to find out what their needs, wants and worries were, and to introduce them to the design process, instead of just getting what they would be given.

"We had some experience of this in Ballymun and also in the UK and, although it can be difficult, it can also be very rewarding. As architects, it's great to meet the people you're housing because it focuses you in a way and makes you do a good job. So we ended up having 10 meetings in Aungier Street community centre."

By then, less than 60 of the York Street flats were occupied and the city council had agreed to sell a third of the site to the Royal College of Surgeons in Ireland, whose main teaching building is directly opposite.

The flats were also plagued by "quite serious crime, health and safety issues", according to Seán Harrington.

The brief was to provide 66 new homes on a relatively tight site, and the residents made it clear that they wanted a variety of apartments, duplex units and townhouses.

"Right at the beginning, they also said the things we wanted to hear about building 'eco-homes' with waste control and even a composter," he says.

Architecturally, the new building turns the corner at York Street and Mercer Street, heralding its presence with a flourish; previously, there was only a blank gable here. It is arranged around a Scandinavian-style courtyard, divided into useful compartments - including a sedum-roofed and timber-clad recycling centre.

Rainwater is harvested in large stainless steel drums, from which it can be drawn to water a variety of shrubs, vegetables and fruit trees. There's also a seating area, which conceals the basement carpark vents, a playspace for kids and a portico formed by a pair of salvaged Georgian doorcases, set back-to-back. The apartments, all dual-aspect, are arranged in a U-shaped block around the courtyard, with five cores of lifts and staircases serving just two apartments per floor.

To the rear, where the back yards used to be, there is a range of three-storey mews buildings - separated from each other to let the sun come through.

The footprint of the apartment and mews pavilions is quite shallow, at just 11 metres (compared to 13 or 14 metres for most private apartments). Spatially, they are very generous, with 85sq m (915sq ft) for two-bed apartments and nearly 110sq m (1,184sq ft) for three-bedroom duplexes - well ahead of minimum standards.

With the city council's backing, Seán Harrington Architects extended the environmental agenda to include very high levels of insulation (using sheep's wool, incidentally) as well as glazed shutters on balconies, so that they can become winter gardens, and solar thermal panels on the roof, to supplement gas boilers.

"We just thought that all of this was best practice, even though it was way in excess of Building Regulations at the time," Harrington says. "As a result, each home in the scheme will have a BER (Building Energy Rating) of A3 or B1, which is still higher than what's required by the latest Building Regulations."

As if that wasn't enough, all of the timber joists in the old flats were salvaged and re-used in the timber-frame construction of the new mews housing as well as "green" cement from Ecocem for the concrete casting.

Even MDF was shunned in favour of plywood and chipboard for the kitchen units and wardrobes.

There are no PVC drainpipes either; stainless steel was used instead. Lime mortar, rather than cement, was used to point the brickwork, which is "stacked" on the street elevations to show that it is merely a cladding material. And every balcony has been supplied with a built-in planter - another Scandinavian touch (project architect Jim Roche lived in Finland for a while).

On both street frontages, steel bands delineate the extent of each apartment while the projecting bay windows all have side windows in different colours to give a sense of individuality. "But street elevations in a sensitive location like this need to be polite and have certain uniformity," Harrington says.

Echoing the Georgian idiom, a railed dry moat on York Street "keeps people away from the windows", with short bridges leading to entrances.

Granite gate piers were carved to provide children's seats and the architects have even designed a 10-panel art work in baked enamel illustrating the area's history.

On Mercer Street, the balconies are diagonally arranged so that residents enjoying the afternoon sun will always just have the sky over their heads.

The balustrades are also solid, rather than glazed, to provide a greater degree of privacy - and also to conceal bikes and toys that would otherwise be visible. In the seven-storey corner tower, rendered in cobalt blue, the balconies are "stacked like drawers" to reinforce its verticality.

Solar panels are integrated into the design, as is a south-facing roof garden from which there are great views; pity about the incessant noise from the Mercer Hotel's air-handling units opposite.

Extract vents from the plant rooms read like Georgian chimneys - a device also used by Grafton Architects on their great new building for the Department of Finance on Merrion Row. It is also possible to see right through the apartment block on York Street to the garden, or rather "outdoor room", in the courtyard.

The completed scheme, with its lavishly furnished showflats (all with lots of storage space), contrasts with the grim blocks of flats on the west side of Mercer Street, built by Dublin Corporation in the 1970s - none of which addresses the street; they're almost crying out for demolition and replacement.

Built by McNamara for €16 million (including fees), the York Street housing may be the swansong of a particular form of procurement and seems unlikely to be replicated elsewhere.

The critical thing now is that it gets good estate management, most effectively involving its justifiably delighted residents.