expression, godan verb (-su)
do something useless; gild the lily; build a roof atop the roof
Idiomatic expression meaning to do something redundant or unnecessary, like adding a roof on top of an existing roof. Often used to criticize superfluous effort.
See also: 屋上架屋
Adding more data to this report would be like gilding the lily.
彼の提案は屋上屋を架すだけで、何の役にも立たない。
His suggestion is just building a roof atop the roof; it serves no purpose.