The judgment of the first instance court, including the plaintiff's claim expanded and reduced in this court, is modified as follows.

According to the purport of Gap evidence Nos. 2, 3, 5, 6, 7, 8, and 10 (including paper numbers) and the entire pleadings as to the cause of the claim, the defendants are co-owners of building E (hereinafter "the building of this case") newly constructed in Yeonsu-gu Incheon Metropolitan City, and the plaintiff is a person engaged in household production and building business, and F was a site manager who has overall management of the construction site of the building of this case. The plaintiff was commissioned by F from F on January 18, 2019 to manufacture and install the main furniture and attached houses (hereinafter "the construction of this case") among the new construction of the building of this case, and submitted a estimate of construction price of 21,00,000,000 won, and the plaintiff can be recognized on January 1, 2019 to undertake construction works for households, such as the construction of a household, with the payment of construction price of KRW 10,000,000,000,000.

Therefore, at the construction site of the instant building jointly constructed by the Defendants, the costs that the Plaintiff did not incur (i.e., KRW 11,000,000 - KRW 10,000 - KRW 2,100,000). Since the value-added tax that was not paid is KRW 2,100,000,000, the Defendants jointly have the obligation to pay to the Plaintiff damages for delay calculated by the annual rate of 13,100,000 (=11,000,000 KRW 2,10,000) and the damages for delay calculated by 12% per annum under the Act on Special Cases Concerning the Promotion, etc. of Legal Proceedings from April 2, 2019 to July 7, 2020, which is the date the judgment of this court rendered that it is reasonable for the Defendants to dispute the existence or scope of the obligation to perform.

The plaintiff sought the payment of damages for delay calculated at the interest rate prescribed by the Act on Special Cases Concerning the Promotion, etc. of Legal Proceedings from the day following the delivery of a copy of the application for modification of the purport of the claim and the cause of the claim. However, if the defendant asserted the existence and the scope of the obligation and accepted