THE Department of Mechanical Engineering, Trinity College, by Grafton Architects. Trinity College has established an enviable reputation for the high architectural quality of its new buildings over the past 30 years - from the Berkeley Library, completed in 1967, to the more recent O'Reilly Institute on Westland Row, the Beckett Theatre and the remaking of Aras an Phiarsaigh.

The college's commitment to contemporary architecture is all the more commendable given that it is also the custodian of the largest single complex of historic buildings in Dublin. Pastiche has never been part of its agenda; if new buildings are required, they all bear the unmistakable mark of the late 20th century.

The £1.2 million extension to the Parsons Building, for the Department of Mechanical Engineering, is no exception. Designed by Grafton Architects, it has been described in the Irish Architect as "one of the finest buildings built in Ireland in recent years, very much in the tradition of contemporary European modernism".

The architects were faced with a complex brief and a very difficult site. They were asked to provide highly serviced laboratories and workshops, with ancillary seminar rooms and study areas, linked with the existing mid 19th century Parsons Building, which had been built at an angle to the college's geometry, parallel to Lincoln Place.

Appropriately, the new building is aligned with an extension to the Dental Hospital, now under construction. Its most striking feature, a raised "cube" clad in black basalt, may look somewhat out of place at first sight, but it is carefully aligned with the Chemistry Building, which follows the long established grid of Trinity. Grafton Architects had to fight for their openjointed basalt cladding, which is honed to give it a mild sheen. Dublin Corporation's planners, gripped by fear of the unknown, tried to insist on the more familiar Portland stone, but eventually relented on the issue. (The basalt will look even better when the Parsons' facade is cleaned).

The black "cuboid", housing a fluids laboratory, "floats" over an irregularly shaped podium which roofs the two main workshops - one lit by three sharp edged triangular rooflights and the other by a clever combination of clerestory and narrow horizontal windows, set into the Wicklow granite plinth just at eye level.

The interiors, with their mesmerising array of machinery, are highly functional. Some of the concrete work, particularly on the stepped ramp, is quite rough - in contrast to the polished, pigmented plaster of the building's "bookend", which links it to its Victorian neighbour and to the Dental Hospital extension.

This is architecture with guts, a highly refined "in your face" job, which challenges the misconceived notion that any extension to a historic building should plagiarise its style. Some people will find it disturbing, but there can be no doubt that it is the product of a considered design process, executed with great conviction.