## 1 Introduction  
One of the most common complaints about the sound environment in Korean multi-family housing is floor impact noise from the upper and lower floors. To solve these complaints, the government, construction companies, and various research institutes are conducting various studies [1, 2, 3, 4, 5]. Representatively, the development of resilient materials floor structures, the design of ceiling structures for soundproof rooms, and the planning of low-noise layouts are notable advancements. These technological developments are incorporated into the design of multi-family housing [6, 7, 8, 9, 10]. In addition, the government has revised the official guidelines concerning the evaluation of impact sound between floors in multi-family housing; including changes in the sources of impact and the evaluation methods, in accordance with the international standard ISO 16283-2, ISO 717-2 etc. [11; 12; 13]. The representative resilient materials inserted into the floor structure of multi-family housing for the purpose of reducing impact sound are EPS (expanded polystyrene) and EVA (ethylene vinyl acetate). These materials are used in floor cushioning structures that have been previously approved by the government, specifically those that have obtained certification. This system is referred to as the pre-certification system. In the case of resilient material certification, in Korea, it is common to install floor impact sound test buildings using 59 m\({}^{2}\) and 84 m\({}^{2}\) configurations. These test buildings are designed to be identical to actual multi-family housing. Once the installation of the floor structure is complete, measurements and evaluations are conducted to assess the impact sound insulation performance, including for both lightweight and heavy-weight impact sounds. For floor structures that have completed the evaluation, the certification grade of the installed resilient materials floor structure is determined based on the highest result obtained from the 59 m\({}^{2}\) and 84 m\({}^{2}\) test configurations. However, despite the installation of certified floor structures in actual multi-family housing, there are instances where the expected impact sound insulation performance does not meet the certified standards. Such issues may stem from various factors, including changes in the floor plan configuration of multi-family housing and the homogenization of bare slab structures. Additionally, the quality of work-manship at the construction site and flanking transmissions occurring between specific rooms on different floors may also contribute to these issues. As a result, residents of multi-family housings are experiencing disturbances related to impact sound transmission between floors. To address this floor impact sound issue, the government has revised the official guidelines to require measurement and evaluation of floor impact sound at the completion stage, prior to the inspection of multi-family housing, in order to certify the results. This system is referred to as the post-certification system. With the introduction of the mandatory post-certification system for measuring on-site performance at the pre-inspection stage of resilient materials floor structures in multi-family housing, it has become possible to assess the floor impact sound insulation performance of newly supplied housing units. This system is also regarded as a fundamental measure for addressing impact sound complaints in actual multi-family housing. The key elements of the post-certification system for floor impact sound include the requirement that the entity responsible for the housing project, after obtaining approval for the project plan, undergoes performance testing by an accredited inspection agency to evaluate the sound insulation performance of the floor impact sound barrier structure. The results are to be submitted to the authority responsible for the final inspection.