## 3 Methodology  
### Description of the Studied Housing Units  
Field measurements of the water supply and drainage noises from the bathroom were carried out in 14 types of housing units with different floor areas and plans. The floor areas considered in this study are 33 m\({}^{2}\), 36 m\({}^{2}\), 46 m\({}^{2}\), 59 m\({}^{2}\), 74 m\({}^{2}\), and 84 m\({}^{2}\), and they represent the area for exclusive use. Different floor plans with the same floor area were also selected to examine the characteristics of the \begin{table}
\begin{tabular}{c c} \hline
**Receiving Room** & **L\({}_{\text{Amax}}\) (Slow Response) (dB)** \\ \hline Residential bedroom, living room, dining room & 35 \\ Residential bathroom, kitchen & 45 \\ \hline \end{tabular}
\end{table} 
Table 4: Recommended maximum A-weighted SPL for various transient plumbing-noise sources in buildings (ASHRAE handbook). \begin{table}
\begin{tabular}{c c} \hline
**Tier** & **Criteria** & **Weighting Factors** \\ \hline
1 & 9 points or above & 1.0 \\
2 & 7 to 8 points & 0.75 \\
3 & 5 to 6 points & 0.5 \\
4 & 4 points and below & 0.25 \\ - Dwelling-water-supply pressure less than 2.5 kgf/cm\({}^{2}\): 3 points \\ - Low-flow toilet less than 6 L, single-flush (or 9 L/5 L, dual-flush): 2 points \\ - Installation of buffer at pipe-crossing slabs: 1 point \\ - Low-noise drainage pipe: 2 points \\ - In-floor type for water supply and drainage pipes: 4 points \\ - Noise-reduction measure for air ducts: 2 points \\ \hline \end{tabular}
\end{table} 
Table 2: Criteria and credits in G-SEED for measures to reduce water supply and drainage noises. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Type of Space and Sources** & **Quantity** & **Class A** & **Class B** & **Class C** & **Class D** & **Class E** & **Class F** \\ \hline In habitable rooms in dwellings from & & & & & & & \\ service equipment, producing & & & & & & & \\ intermittent or irregular noise from & \(\leq\)26 & \(\leq\)30 & \(\leq\)34 & \(\leq\)38 & \(\leq\)42 & \(\leq\)46 \\ neighboring spaces & & & & & & & \\ \hline \end{tabular} \({}^{(1)}\) L\({}_{\text{ASAmax,LT}}\) may also be used, provided that 4 dB stricter limits (lower sound levels) are fulfilled, i.e., the same as the L\({}_{\text{Aeq,nT}}\).  
\end{table} 
Table 3: Class limits for service equipment noise from neighboring spaces (The 2 nd ISO/CD 19488). sound propagation from the bathroom to the adjacent room. The type of housing unit is distinguished by a symbol that indicates the floor area with a number and a plan in an upper-case letter (e.g., 59A = A type of 59 m\({}^{2}\)). The number of bathrooms in the housing units with a small floor area between 33 m\({}^{2}\) and 46 m\({}^{2}\) is one, while the housing units with a large floor area between 59 m\({}^{2}\) and 84 m\({}^{2}\) contain two bathrooms that are attached to the living room and bedroom. Figure 1 shows the 14 floor plans of the studied housing units with different floor areas. Figure 1: _Cont._  
For each type of housing unit, the measurements were also conducted on different floors to examine the fluctuation in noise level due to the altitude of the bathroom in multi-residential buildings with a maximum of 28 floors. The floor in the multi-residential buildings was selected by including the ground, middle, and top floors. Although it depends on the total floors of a multi-residential building, the number of selected properties is between four and six units with a step of the fifth floor. Table 5 lists the numbers of bathrooms and properties that were measured in the buildings. As described in Table 5, the total number of the studied housings where the noise level in the bathroom of the lower floor was measured according to the use of sanitary wares including the water closet, basin, and bath is 64 (113 bathrooms).