Plumbing Drainage Design Code

Building Plumbing and Drainage Equipment Design Code

Overview

This skill provides technical design and compliance evaluation procedures for building cold/hot water supply systems, drainage systems, ventilation piping, trap seal protection, cleanouts, same-floor drainage, and grease interceptors in Taiwan. It is based on Taiwan's official Technical Code for Building Plumbing and Drainage Equipment Design (建築物給水排水設備設計技術規範, per Building Technical Regulations Equipment Code Article 26).

Use this skill when:

• Designing or auditing water storage tank capacities (受水槽, 屋頂水塔) and maintenance clearances.
• Sizing water supply pipes using Water Supply Fixture Units (WSFU) and verifying pressure limits (0.3–3.5 kg/cm²).
• Calculating drainage pipe diameters (DFU) and minimum slopes (1/50 for 3065mm, 1/100 for 75100mm, 1/200 for ≥150mm).
• Checking trap seal depth (5–10 cm), avoiding double trapping, and reviewing same-floor drainage (同層排水).
• Verifying cleanout intervals (≤15m for ≤100mm, ≤30m for ≥125mm) and operating clearance (30–45 cm).
• Configuring vent systems (stack, individual, loop, yoke, relief, wet vent, AAV) and roof termination heights.
• Selecting and sizing manufactured grease interceptors (油脂截留器) per Appendix formulas.

Execution Steps

1. Step 1: Water Supply System Audit (§3.1 – §3.2, Appendix 1)

   • Determine total daily water consumption based on building occupancy and per-capita demand table (Appendix 1.1).
   • Verify storage tank volumes (§3.2.3):
     • Receiving tank (受水槽): $\ge 2/10$ of daily demand (typically 0.5 day).
     • Elevated roof tank (屋頂水塔): $\ge 1/10$ of daily demand.
     • Combined storage volume: $4/10 \le V_{\text{total}} \le 2.0$ days of daily demand.
   • Inspect tank physical clearances (§3.2.1 – §3.2.2):
     • Double-wall requirement: Tank walls/slab must not be shared with building structural walls/slabs.
     • Maintenance clearances: Side clearance $\ge 60\text{ cm}$ (or $\ge 45\text{ cm}$ near structural columns); top manhole and top slab clearance $\ge 60\text{ cm}$ (§3.2.2, §3.2.2(3)); bottom-to-slab clearance $\ge 20\text{ cm}$ (§3.2.2(4)) with a drainage sump.
     • Sloped bottom $\ge 1/50$ toward drainage outlet.
     • Air gap for water inlet $\ge 50\text{ mm}$ or $\ge 1 \times \text{pipe diameter}$ above overflow level (§3.2.6).
   • Check pressure & velocity limits (§3.1.3, §3.4.4):
     • Minimum residual pressure at fixtures: $0.3\text{ kg/cm}^2$ ($30\text{ kPa}$), or $1.0\text{ kg/cm}^2$ for direct flush valves.
     • Maximum fixture pressure: $3.5\text{ kg/cm}^2$ ($350\text{ kPa}$) — install pressure reducing valves (PRVs) if exceeded.
     • Maintain proper flow velocity in pipes to prevent water hammer and noise.

2. Step 2: Drainage & Vent System Sizing (§4.1 – §4.3, Appendix 3)

   • Calculate Drainage Fixture Units (DFU) for horizontal branches, stacks, and building drain.
   • Verify minimum pipe slopes (§4.2.3):
     • Pipe diameter $D = 30\text{--}65\text{ mm}$: Slope $\ge 1/50$ (2%).
     • Pipe diameter $D = 75\text{--}100\text{ mm}$: Slope $\ge 1/100$ (1%).
     • Pipe diameter $D \ge 150\text{ mm}$: Slope $\ge 1/200$ (0.5%).
   • Verify horizontal branch length $\le 12\text{ m}$ and maximum 4 bends to ensure solids conveyance (§4.2.16).
   • Verify trap seal depth (§4.4.4): $5.0\text{ cm} \le D_{\text{seal}} \le 10.0\text{ cm}$ ($50\text{–}100\text{ mm}$). Distance from fixture outlet to trap weir $\le 60\text{ cm}$ (§4.4.3). Check for prohibited double traps.
   • Check cleanout placements (§4.5):
     • Maximum interval: $\le 15\text{ m}$ for pipe $D \le 100\text{ mm}$; $\le 30\text{ m}$ for pipe $D \ge 125\text{ mm}$.
     • Required at branch origins, direction changes $> 45^\circ$, stack bases, and building drain connections.
     • Clearance around cleanout: $\ge 45\text{ cm}$ for $D \ge 75\text{ mm}$; $\ge 30\text{ cm}$ for $D < 75\text{ mm}$.

3. Step 3: Ventilation System Verification (§4.3)

   • Stack vent (伸頂通氣管): Height above roof $\ge 15\text{ cm}$ ($\ge 1.5\text{ m}$ if roof is accessible/garden/terrace) (§4.3.8).
   • Individual vent (個別通氣管): Diameter $\ge 1/2 \times D_{\text{drain}}$ and $\ge 30\text{ mm}$ (§4.3.2).
   • Loop/Circuit vent (環狀通氣管): Recommended when serving $\ge 8$ fixtures (or $\ge 3$ water closets) per loop (§4.3.12).
   • Yoke vent (結合通氣管): Required every 10 branch intervals/floors for stacks serving $\ge 10$ branches (§4.3.14). Connected below the branch line on the drainage stack, terminating $\ge 90\text{ cm}$ above floor level on the vent stack.
   • Air Admittance Valve (AAV, 吸氣閥): Must be CNS/ISO certified; installed $\ge 15\text{ cm}$ above the flood level rim of the highest served fixture (§4.3.16).

4. Step 4: Grease Interceptor Sizing (§4.6, Appendix 5)

   • Required for commercial kitchens, restaurants, food preparation areas (§4.6.2).
   • Determine effective volume $V$ (Liters) based on dining area ($m^2$) or meal count per Appendix formulas. Ensure trap seal depth $5\text{--}20\text{ cm}$ on outlet and provide gas-tight cover (§4.6.3).

Requirements & Constraints

• Standards Basis: Taiwan Technical Code for Building Plumbing and Drainage Equipment Design (建築物給水排水設備設計技術規範) & CNS national standards.
• Unit System: Metric (mm, cm, m, kg/cm², L/min, m/s).
• Prohibited Configurations:
  • No direct connection between potable water and non-potable/drainage systems (cross-connection).
  • No sharing of water tank walls/slabs with building structure (double-wall mandatory).
  • No double trapping (雙重存水彎).
  • No direct pumping from municipal water mains.

Worked Example

Example 1: Water Tank Volume & Booster Pump Calculations

Scenario: An 8-story residential building with 32 units, 4 occupants per unit ($N = 128$ occupants). Daily water consumption benchmark $q = 250\text{ L/person/day}$.

1. Daily Total Demand ($Q_d$): $$Q_d = 128 \times 250 = 32,000\text{ Liters/day} = 32\text{ m}^3\text{/day}$$
2. Receiving Tank Volume ($V_{\text{rcv}}$) per §3.2.3: $$V_{\text{rcv}} = 0.5 \times Q_d = 16\text{ m}^3 \quad (\text{meets }\ge 2/10 = 6.4\text{ m}^3\text{ minimum})$$
3. Roof Tank Volume ($V_{\text{roof}}$) per §3.2.3: $$V_{\text{roof}} = 0.2 \times Q_d = 6.4\text{ m}^3 \quad (\text{meets }\ge 1/10 = 3.2\text{ m}^3\text{ minimum})$$
4. Combined Storage Check: $$V_{\text{total}} = 16 + 6.4 = 22.4\text{ m}^3 = 0.70 \times Q_d \quad (\text{within requirement } 0.4 \le V/Q_d \le 2.0)$$
5. Physical Space Clearance Verification (§3.2.2):
   • Side maintenance space: $60\text{ cm}$ minimum surrounding all 4 sides.
   • Bottom-to-slab clearance: $30\text{ cm}$ ($> 20\text{ cm}$ min) on concrete pedestals with sump.
   • Top manhole and top-to-ceiling clearance: $60\text{ cm}$ minimum (§3.2.2, §3.2.2(3)).

Example 2: Horizontal Drainage Branch Sizing & Cleanout Check

Scenario: A commercial floor drainage horizontal branch serving 6 water closets (6 DFU each) and 4 lavatories (1 DFU each). Total $\text{DFU} = 6 \times 6 + 4 \times 1 = 40\text{ DFU}$. Total branch length $L = 14\text{ m}$.

1. Pipe Diameter & Slope Selection (§4.2.3, Appendix 3.1):
   • For $40\text{ DFU}$ horizontal branch, required nominal pipe size is $100\text{ mm}$ ($4"$).
   • For $D = 100\text{ mm}$, mandatory minimum slope is 1/100 (1.0%).
2. Cleanout Spacing Verification (§4.5.1):
   • For $D = 100\text{ mm}$, maximum allowed cleanout spacing is $15\text{ m}$.
   • Since branch length $L = 14\text{ m} \le 15\text{ m}$, a cleanout at the branch origin + end of line is compliant.
   • Cleanout operating clearance (§4.5.3): $45\text{ cm}$ clear space around the $100\text{ mm}$ cleanout cover.