A. A. Around April 6, 2018, the Plaintiff was awarded a contract with D (Co., Ltd.) and Defendant C to the 319,000,000,000 (including value-added tax) for the construction cost of a bowling site remodeling project on the first floor of the building located under Dongdaemun-gu Seoul building E (hereinafter “instant construction project”).

B. After that, around October 31, 2018, a contract was concluded for the change of the contractor to the Defendants, and the total construction cost increased to KRW 324,50,000, and the Plaintiff completed the construction.

C. The Defendants paid a total of KRW 293,300,000 to the Plaintiff as construction cost with respect to the instant construction work.

On the other hand, there are parts related to the construction of this case such as partial modifications, construction parts and defects, and the results of the appraisal of this court are as follows.

[Reasons for Recognition: Facts without dispute; Gap evidence 2 and 12; Eul evidence; Eul evidence 9; witness D's partial testimony (except for the part not trusted in the rear); appraiser F's defect appraisal result; the purport of the whole pleadings]

2. Determination

A. The final construction cost related to the instant construction project is KRW 324,500,000 (the Defendant’s assertion that the amount was reduced to KRW 319,000 from KRW 324,50,000 to KRW 319,000 in relation to the existing construction cost is proved to have been dismissed after the conclusion of the contract) Here, the Defendants’ deduction of KRW 293,30,000 that the Defendants paid to the Plaintiff as the instant construction cost from the deduction of KRW 293,30,000 that the Defendants had to pay to the Plaintiff would remain 31,20,000.

B. After the arrival of the Defendants’ various claims for mutual aid, the Defendants were examined on the basis of the preparatory brief dated June 8, 2020, which was finally arranged after their arrival.

(1) - The Defendants who did not accept the portion of the non-construction or defect related to fire prevention facilities - The Defendants, even though they promised the first D to complete all the construction related to fire prevention facilities, ordered the Plaintiff to complete the construction related to the fire prevention facilities, but the cost of the construction due to the non-installation of the combustion boundary wall 10,000 won and the reduction of the construction cost and the heat reduction defect 2,145,00 won.