Apartment Liquid Waterproofing Minimum Thickness Standard Should Be Set at 4 mm

Published 11 Feb.2026 15:00(KST)

In a lawsuit seeking damages for defects in the liquid waterproofing layer of an apartment building, a court has ruled that the minimum thickness standard for calculating the cost of defect repair should be set at 4 mm. The 3-1 Civil Division of the Seoul High Court (Presiding Judges Kyeon Jongcheol, Choi Hyunjong, and Bae Yongjun) partially ruled in favor of the plaintiffs on November 5, 2025, in a damages suit (Case No. 2023Na2025399) filed by residents against the contractor Yuseong Construction and others. The appellate judgment became final and binding after the plaintiffs withdrew their appeal to the Supreme Court.

The Law Times

[Facts and Issues]

The plaintiffs filed a damages lawsuit on October 22, 2020, over various defects such as leaks and cracks. The key issue was the thickness of the liquid waterproofing. The liquid waterproofing thickness refers to the final thickness of the waterproof mortar made by mixing cement, waterproofing agent, and water. If the construction falls short of the standard thickness, it is deemed a defect and serves as the basis for calculating the cost of defect repair.

[Lower Court Judgment]

The court of first instance held that, based on the standard material quantities for building works, the cost of defect repair should be calculated using 6 mm for walls and 10 mm for floors as the standard, and ordered the contractor to pay 2,103,400,000 won to the residents.

[Appellate Court Judgment]

The appellate court held that the minimum thickness of the liquid waterproofing layer should be set at 4 mm for walls and 4 mm for floors when calculating the cost of defect repair, and ordered the contractor to pay 1,806,530,000 won to the residents. The bench stated, "In light of the purpose of the 2013 Standard Specifications for Building Works, which prescribe 4 mm as the minimum thickness of the waterproofing layer at which the adhesion performance of waterproofing work can be evaluated, it is reasonable to regard cases that do not reach 4 mm as defects." The court found it difficult to continue applying the previous thickness standards from 1994 (6 mm and 10 mm), which had been explicitly deleted. The Standard Specifications are basic construction standards for building works established by the government and serve as standard regulations that clients and construction companies must follow.

[Counsel’s Opinion]

Attorney Lee Dongguk of law firm Dongin (28th class of the Judicial Research and Training Institute) said, "With this ruling, contractors will be able to save unnecessary costs." He added, "If a client determines that a higher level of waterproofing performance is necessary, it will specify concrete figures from the design stage."