During the Civil War, Republican forces revived their campaign to burn down big houses. The campaign was facilitated by the absence of any forces of law and order in the countryside as a result of the withdrawal of the Crown forces in 1922 and the abolition of the RIC, but the elimination of signs of British rule in Ireland was the underlying motivation behind the destruction. The Republicans were also running dangerously low in arms so destruction of property was one of few acts of guerrilla warfare left at their disposal.
The big houses were burned down during the War of Independence as a way for the IRA to assert their authority. However, during the Civil War, many of the mansions abandoned by their owners for fear of attack were taken over by the anti-Treatyites and only destroyed when they were forced to leave when the National Army moved in on them.
Below were a few of many set alight in early 1923:
January 29 The Earl of Mayo’s Dublin residence is set alight by Republicans.
Sir Horace Plunkett’s Art Treasures are Destroyed
1 February: Moore Hall near Claremorris in County Mayo is burned down by Republicans.
Irish Times 6 February 1923
Freeman’s Journal 6 February 1923
Weekly Freeman’s Journal 3 February 1923
Further reading: https://www.con-telegraph.ie/2021/01/30/the-burning-of-moorehall-house-almost-a-century-ago/