The train hall at Heuston station is to get its first major overhaul in 160 years, with a total reroofing of the structure as part of a €13 million upgrade.
The largest covered area in Ireland or Britain when it was built in 1844, the hall needs a refit because of safety concerns about the current state of the structure.
Iarnród Éireann has said there will be no disruption to rail services for the 30,000 passengers who will use the station during the 18-month refit of the iron structure, which will begin next January.
The station currently caters for 40 Intercity and 36 commuter trains each day, which the company said would continue throughout the refit.
The main aspect of the refurbishment will be the replacement of 390 wrought-iron roof trusses with mild-steel structures.
Each of 64 cast-iron columns that hold up the roof will also be checked for structural integrity.Some of the columns have eroded on the inside as they formed the original drainage system. It is estimated that up to 15 will have to be replaced.
The current timber roof, with plastic see-through sections, which covers 8,500 square metres and five train platforms, will be replaced - in some parts with glass. The original profile of the roof will be reinstated through a "lantern" feature, which originally provided for ventilation.
A spokesman for Iarnród Éireann said that, although there had been ongoing maintenance, it now required a major refit.
"It does need to be done. If it's not done now, it will become a safety issue," he said.
Heuston station and the train hall is a listed building, and Iarnród Éireann said it had consulted various heritage experts and organisations while developing its plans. A spokesman said the refit would protect key features of the original design.
"It's the first major upgrade, as far as we are aware, since it was constructed in 1844," said Mr John Clancy, the train company's chief architect. He said the train hall, originally built in 18 months, was one of the earliest constructed. It was designed by Sir John Benjamin MacNeill, the first professor of civil and structural engineering at Trinity College.
Mr Clancy said it was a "major wonder" at the time, and was lit by 72 gas lights.
When it was built, it served only one rail line, however, which went as far as Carlow. The original five platforms were the only ones available for 150 years until the recent development.
The train hall project is the latest phase in the entire overhaul of Heuston station, which included four new platforms and a remodelled public concourse.