One of Dublin’s most architecturally significant buildings is to resume use as a secondary school after lying idle for almost 15 years.

Rathfarnam's Loreto Abbey, which dates back to the 18th century, is to house Gaelcholáiste an Phiarsaigh, the first all-Irish secondary school to be established in south Dublin since Tallaght's Coláiste de hÍde was founded in 1993.

The former boarding school was recently purchased from Nama by the Department of Education for a reported €2.3 million and will reopen for lessons in September.

The huge growth in demand for Irish language schooling has intensified the need for Irish language post-primary schools to accommodate the numerous Gaelscoileanna that have sprung up across Dublin city and county in recent years.

There are currently only seven post-primary schools catering for some 34 all-Irish primary schools in the region, and south Co Dublin is serviced by just three post-primary schools - Coláiste Eoin and Íosagáin in Stillorgan and Coláiste de hÍde in Tallaght.

The new post-primary school will be multi-denominational and will cater primarily for pupils from Gaelscoil Thaobh na Coille in Kilternan, Lios na nÓg in Ranelagh, Scoil Mológa in Harold’s Cross and Gaelscoil Chnoc Liamhna in Knocklyon.

Some 200 children have already registered with the school and 46 are enrolled to start in September. It is envisaged that this number will increase to between 500 and 600 once the school is fully operational.

After campaigning for 10 years for a site to house an Irish language post-primary school in the area, parents were told in January that the Department of Education had identified a permanent location suitable for the school.

Commercial sensitivities surrounding the purchase of the site meant the location was only revealed this week.

Speaking this morning, chairman of the school board, Lorcán Mac Gabhann, said he had been informed on Monday that the new school will be housed in the former abbey from September.

He said the news brought a sense of relief to parents who had become frustrated at the absence of a premises as the new school year approached. The school will now concentrate on enrolment and determining the number of teachers required.

“One major element was missing - the location of the school. Everything else depended on that,” Mr Mac Gabhann said, adding he hoped the attendance will be finalised soon.

The school board is holding a meeting for prospective parents in Bewleys Hotel in Leopardstown at 8pm tonight to discuss the latest developments.

“We are expecting 100 people at the meeting tonight. People are coming back who had registered for other schools.”

An Foras Pátrúnachta, the patron body for the school, welcomed the development. General secretary Caoimhín Ó hEaghra said: “We are delighted that the school has found a permanent site at last.

“There has been a clear demand for a Gaelcholáiste in this area for a long time and this can be seen in the level of demand for places in Coláiste Eoin and Íosagáin. We hope the new school will cater for the need that is there at the moment and that we will see in the future.

Mr Ó hEaghra said some renovations would be required to bring the building up to current standards, but that An Foras Pátrúnachta was working on this with the Department of Education.

Built in 1725 by William Palliser, the original house was purchased by Archbishop Murray of Dublin in 1821 for the Irish branch of the Institute of the Blessed Mary. Described as early Georgian and classical in style, the main abbey building is where the school will initially be housed.

The 1.82 hectare site consists of several buildings including the abbey itself, a concert hall, a church, a gymnasium and two gate lodges.

A boarding school was established on the site in 1823 and the property was extended between 1863 and 1903 to include the concert hall and gymnasium.

Previously run by the Loreto Sisters, the school closed in 1999 and was purchased by property developer Liam Carroll for £14 million.

He planned to convert the property into a nursing home and to build 10 apartment blocks. He failed in his attempt to convert the former convent buildings into offices in 2004 and the site was subsequently taken over by Nama.