The problem of declining numbers in religious orders in recent years and the resultant closure of monasteries and convents has in turn created another difficulty: what should be done with these buildings?

While the main blocks can be converted with relative ease into apartments, and the grounds used for housing, it is much less easy to find a new purpose for the structure which has stood at the heart, both literally and metaphorically, of a religious community - the chapel.

What many observers find particularly extraordinary is that the monks, nuns and priests who have been custodians of these buildings for so long should show so little concern for their plight.

Churches have, of course, been refurbished for a variety of different purposes over the past decade. Initially, the majority of these were former Church of Ireland premises, made redundant by falling numbers of parishioners. More recently, the Roman Catholic church has also been disposing of some de-consecrated sites; SS Michael and John's in Dublin's Temple Bar, for example, is now a Viking Heritage Centre.

In the capital, and elsewhere, old churches have become offices, retail outlets and bars. With regard to the last of these uses, it is noteworthy that the majority of Ireland's pubs given a pseudo-Victorian makeover in the 1990s were decorated with recycled church furnishings. But all these buildings have been free-standing and therefore not too difficult to convert. Their interiors, as a rule, are relatively plain although that was not the case with SS Michael and John, which had charming neo-Gothic decoration surviving only in part.

Much more awkward when it comes to finding alternative uses are the churches and chapels now starting to come on the market. These were built specifically for the religious orders they have served until recently and can have elaborate interiors. What might almost be a test case of such buildings is St Alphonsus Chapel in Drumcondra, at present offered for sale by owners Shannon Development.

This listed building is attached to a convent occupied until recently by an enclosed order of nuns for whom the chapel was built in 1873. Its architect was George Ashlin, who during the previous decade had been in partnership with Augustus Welby Pugin, the 19th century's foremost advocate of Gothic architecture. While there are elements of the Gothic in this chapel, it also incorporates Palladian and Baroque features and, over the high altar, a top-lit dome.

However, the architectural complexities of the structure, while fascinating, are less likely to preoccupy potential purchasers than the wondrous decoration of the chapel, the walls of which are covered with inlaid marble. From floor to ceiling, there is hardly any surface left plain as those areas not faced with marble are either painted or carved.

The entire space rises without obstruction except for a gallery at the back of the chapel and this means even more challenges for any new owner; to divide the interior into two storeys, for example, would mean installing a free-standing mezzanine (since anything attached to the walls would damage their decoration) and removing all light from the ground floor as all windows are on the upper level.

Furthermore, the ecclesiastical character of the building is so distinctive that its original purpose could never be obscured and while the interior is dry, it is also cold, so installing effective heating could also prove problematic. The chapel actually occupies only half the total site of 588 sq. m being offered for sale and this may make the proposition more attractive to buyers.

A narrow passage could be opened behind the curved wall of the apse leading to a large room beyond. This in turn opens to a number of spaces, the dividing walls of which could be removed to create a substantial hall. But the chapel takes up so much of the overall area that whoever buys St Alphonsus will have to come up with an imaginative use for an unusual space.

The same difficulties in finding a purchaser are also likely to be faced by the vendors of the chapel attached to the old Loreto Abbey in Rathfarnham. The entire complex was sold last autumn for £14 million to a developer whose options for the convent church are very restricted. Again, the building is listed for preservation and is part of a much larger complex.

In this instance, there may be further problems as the chapel proper has floors both below and above; the former has been used until now as a kitchen while the latter served as dormitories and bathrooms. Pugin worked on the designs of Loreto Convent at the request of Dublin architect Patrick Byrne, who was also responsible for both St Paul's and St Audoen's Catholic churches in central Dublin. Dating from 1839 onwards, its high Gothic interior again contains rich decorative details on walls and ceiling which includes a glazed lantern originally installed to permit sick nuns to follow services at the high altar below.

John Hogan, the finest Irish sculptor of the 19th century, carved a marble pieta for that altar in 1843 and five years later provided flanking marble angels, for which his daughters (one of whom eventually became reverend mother of the convent) acted as models.

The present high altar itself dates from 1894 and was designed by J L Robinson. What purpose, other than its original use, can such a building serve? While the developers here plan to build 10 apartment blocks in the convent grounds and convert parts of the old structure into a nursing home, the chapel itself remains virtually incapable of conversion.

The problems faced here are certain to become more widespread as further monasteries and convents are vacated by former owners and abandoned to the vicissitudes of the Irish property market.