gilding the lily; adding redundant things
A yojijukugo meaning to do something unnecessary or to add something superfluous, often making things worse. Literally 'building a roof on top of a roof'. Used in formal or literary contexts.
See also: 屋上屋を架す
That proposal was gilding the lily; it only caused confusion.
彼の説明は屋上架屋の感がある。
His explanation feels like adding redundant things.
Also means something unnecessary or redundant, but 蛇足 is more common and casual, while 屋上架屋 is more literary and formal.
A yojijukugo derived from the Chinese idiom 屋上架屋, literally 'to build a roof on top of a roof', meaning to do something redundant or unnecessary.