Conservation has become, if not quite a dangerous word, certainly a volatile one. Not merely because we still don't really know exactly what it means. "It seems to make a lot of people nervous, or at least uncomfortable," agrees Mary Hanna, architectural officer of the Heritage Council. Developers don't like it because it usually spells problems, or at least delays, for proposed projects. Our emerging awareness of our long neglected heritage, especially in its architectural context, might well be a case of too little too late, but measures now being taken across the island of Ireland in preserving significant representative architecture of many styles, including the often overlooked vernacular, suggests we now realise there is considerably more to our architectural heritage than the glorious though battered legacy of Georgian Dublin.

Hanna's many projects emphasise that variety. Among her charges are buildings as diverse as Buncrana Castle in Co Donegal, an early Georgian house built about 1718, now felt to be possibly earlier owing to the roof timbers and other details, to a large thatched vernacular farmhouse circa 1705 at Pollwitch, Mayglass, in south Co Wexford, to the charming church of All Saints Dysert Galen, Ballinakill, Co Laois, a neo-gothic structure built in 1821 and, what could be a monumental work of conservation, if sufficient funds are made available, Ballyfin House, Mountrath, Co Laois, once the grandest and most lavish early 19th century mansions in Ireland and since 1927, a Patrician college, now a mixed education secondary day school.

An architect by training, she is practical and about as laid back as a highly efficient individual can be. It was she who coined the phrase "don't get stoned, get plastered", to reform attitudes towards the mistaken current trend of exposing rubble stonework. "Exposed rubble stone walls are not traditional, nor are they healthy for the buildings themselves." Instead she advocates the application of the traditional and efficient lime plaster or wash that served our predecessors so well "by providing a breathable membrane over the walls which kept the buildings dry inside, covered up the rough stonework and produced a pleasing soft textured effect." Hanna is also strongly opposed to the alarmingly popular trend of sandblasting of old stone. "This removes the surface of the stone and exposes it, leaving it wide open to decay." Even worse, is the practice of pointing up joints with a cement mixture. "Cement is far too dense a material to use on this kind of stone work." The cement eventually shrinks leaving hairline cracks. Water then trickles into these openings, can't get out and the wall and the building, become damp.

All of this is explained with logic and enthusiasm. Hanna worries about these buildings but she is not a zealot, keeps her exasperation under control, and is the most good-natured campaigner sensible conservation practices could hope to have. She does not heckle, nor does she impose her expertise. above all, she listens. As many of the in excess of 700 buildings currently on the Heritage Council's list of buildings at risk, developed by Hanna, are in private ownership. Not all are Georgian or Victorian. Her approachable demeanour is a source of confidence for owners aware they are in possession of an important property and are, in most cases, overwhelmed by its conservation requirements. More owners are contacting the Heritage Council for advice on conservation.

Some of these may be routine enquires about limewash and pigments. Others are serious cries for help. During her years in private practice, Hanna, who is married to another architect and has three adult sons, found herself being increasingly drawn to projects involving period houses. Conservation became an interest almost without her realising it. Her involvement with the Heritage Council also began quietly. "I was asked to process the existing grant applications" and then applied for the position of architectural officer.

Appointed in September 1996 she was soon drawing attention to the then imminent demolition of Ssyngefield House just outside Birr, Co Offaly, the seat of the Synge family whose descendants includes the playwright J M Synge. Built in the mid-18th century and fallen into a derelict state, it retains many original features. The house is now on the market under conditions requiring its conservation. Her deliberate, methodical style, inevitably beginning with a careful assessment and detailed reports, is effective. Hanna's desk and shelves of files and reference books at the Heritage Council's offices in Rothe House, the remarkable Tudor complex in Kilkenny city, suggests she is very busy but organised.

Conservation depends on money but she can't over emphasise the information role and the importance of the public understanding of what conservation means to heritage. Her belief in protecting the value of local craft and regional and vernacular style is underlined by the Mayglass project. It was not about providing a local tourism amenity, it was geared for study purposes. The hipped roof farmhouse was repaired by local craftsmen using traditional materials and building techniques. Earth bricks were made in order to repair the mud-walls. Attention to detail was so precise, a national SOS went out in an attempt to source the traditional oaten straw required for the thatching. Nowadays most straw in Ireland is wheaten. Modern farming practices leaves harvested straw unsuitable for thatch, as thatching straw was always harvested slightly green and was allowed to ripen later.

Mayglass shows Hanna is interested in explaining processes, not issuing directives. According to the council's chief executive, Michael Starrett, "Mary pioneered the development of the conservation plan approach in Ireland. It is a tribute to her commitment and professionalism that she was recently elected a fellow of the Royal Institute of Architects in Ireland." In the case of All Saints, Dysert Galen, Ballinakill, she was approached by the rector, the Reverend Patrick Harvey who was concerned by its deterioration. "This church typifies a growing problem in Ireland" says Hanna, "where particularly Church of Ireland churches have small congregations which have difficulty in maintaining the buildings - yet paradoxically these buildings are very important architecturally and historically in their own place." The owners of Bessmount House outside Monaghan town contacted her when the timber turret structure was in danger of collapse. Originally a large Georgian house it was, during the mid-19th century, subjected to an ambitious, almost fanciful high gothic transformation with echoes of a fairytale. "It is another example of private owners being faced with the task of maintaining these wonderful inherited properties."