The Alfred Beit Foundation has said that no works of art were burned in a fire at Russborough House in Co Wicklow last night.
A garda investigation is under way into the fire, which extensively damaged the west wing of the stately home.
The fire was spotted at 9pm by passers-by who alerted the emergency services.
Four units of local fire fighters from Blessington, Dunlavin, Baltinglass and Naas attended the scene.
According to the Wicklow County Fire Service, it took until midnight to get the fire under control; fire fighters remained at the house until 5am to ensure it remained extinguished.
The fire service estimates that 80% of the roof in the west wing was destroyed by the blaze and much of the first floor was damaged. The damage to the ground floor of the wing is said to be less serious.
In a statement, the Alfred Beit Foundation, which runs the house, said the most important thing was that nobody was injured in the blaze.
It said the amount of damage had not been ascertained at this stage, but because the west wing was undergoing renovation, all the contents had been removed from it.
Watch a Nationwide report on Russborough House from 2008
While the house, which dates from 1741, still contains many important art works, the Beit collection's most valuable pieces are housed in the National Gallery.
The art that remains at the estate is held in the main part of the house, and is unaffected by the blaze.
The house is closed to visitors at this time of the year, so the 30,000 tourists who pass through it annually are unaffected.
1 million people have visited Russborough since it opened to the public in 1978, two years after the Beit family gifted it to the people of Ireland.