Chapter 3 · General Regulations
GENERAL REGULATIONS Sections 301–314
Chapter 3 sets the fundamental technical rules that apply to all plumbing work. The two most cited rules: §309 pipe grade (minimum slope for drainage pipes) and §310 direction changes (approved vs. prohibited fittings). Also covers material quality, prohibited practices, rodent proofing, and approved pipe materials.
§301
Quality of Materials
NPC 2000 · Chapter 3 · Section 301
Code Requirement
301.1
All materials used in plumbing work shall be approved, free from defects, and shall conform to the standards cited in this Code or otherwise approved by the Administrative Authority.
301.2
Plumbing fixtures shall be manufactured of dense, durable, non-absorbent material having smooth, impervious surfaces, free from unnecessary concealed fouling surfaces.
301.3
No materials previously used in plumbing work shall be re-used unless such materials are clean, free of defects, and conforming to this Code as if new material.
Dense & Durable
Non-Absorbent
Smooth Impervious Surface
No Concealed Fouling
Re-use Only If Defect-Free
§302
Workmanship
NPC 2000 · Chapter 3 · Section 302
Code Requirement
302.1
Plumbing shall be installed in a workmanlike manner so as to function properly. Piping shall be run in straight lines and at exact grades wherever possible.
302.2
Joints and connections shall be made gas-tight and water-tight for the pressures required under the testing procedures applicable to the system.
302.3
All plumbing shall be properly supported to prevent pipe movement, sag, or strain on joints. Support spacing shall conform to the pipe manufacturer's recommendations and the Code (typically 1.2–3.0 m for horizontal runs, depending on pipe material).
Pipe Support Spacing (typical): Cast iron — 1.5 m horizontal, each story vertical. PVC — 1.2 m horizontal. Copper — 1.5 m horizontal. Always verify with the pipe manufacturer's installation guide.
Support & protection of plumbing systems. Piping is supported at the required intervals to prevent movement, sag, and joint strain, and protected where it passes through framing or is exposed to damage (nail plates, sleeves, escutcheons). Typical horizontal spacing — cast iron/copper ≈1.5 m, PVC ≈1.2 m; vertical piping supported at each floor. (NPC §310 & §312)
§303
Industrial Wastes
NPC 2000 · Chapter 3 · Section 303
Code Requirement
303.1
No industrial waste shall be discharged into the public sewer without first being pre-treated to remove or neutralize substances injurious to the sewer, treatment plant, or receiving waters.
303.2
Interceptors (grease traps, oil/sand separators, acid neutralizers) shall be installed where required to treat industrial or commercial waste before it reaches the public sewer.
303.3
The design of pre-treatment systems shall be approved by the Administrative Authority and, where applicable, by the local Water District (MWSS, LWUA) and DENR-EMB.
Common Industrial Waste Interceptors
| Type | Application | Removes |
|---|---|---|
| Grease Interceptor | Restaurants, commercial kitchens | Fats, oils, grease (FOG) |
| Oil/Sand Separator | Garages, auto shops, car wash | Petroleum, silt, sand |
| Acid Neutralizer | Laboratories, hospitals | Acidic / alkaline waste |
| Hair Interceptor | Barber shops, salons | Hair, solid debris |
| Solids Interceptor | Laundries, food processing | Lint, solids, particles |
§304
Damage to Drainage System
NPC 2000 · Chapter 3 · Section 304
Code Requirement
304.1
No person shall discharge into the drainage system any waste that has a corrosive, damaging, or obstructing effect on pipes, joints, or the sewage disposal system — including strong acids, solvents, molten grease, or materials that solidify at normal temperatures.
304.2
Prohibited discharges include: flammable or explosive liquids, toxic gases, steam or high-temperature liquids (above 60°C / 140°F) without prior cooling.
Hot water limit: Discharge into the sanitary drain must not exceed 60°C. Steam condensate and boiler blowdown must pass through a cooling chamber or dilution sump first.
§305
Prohibited Fittings & Practices
NPC 2000 · Chapter 3 · Section 305
Prohibited Items
305.1
Running Threads: Not permitted in the drainage system. They cannot be properly joined and create leak points.
305.2
Drainage fittings on supply pipes: Drainage-pattern fittings (sanitary T, wye) shall not be used on water supply piping.
305.3
Cement or concrete joints: Not permitted as the primary joint for plumbing pipe connections. Acceptable only for sealing pipe penetrations through slabs/walls.
305.4
Double-hub fittings: Fittings with two bell ends (double hubs) are prohibited unless specifically approved.
305.5
Concealment before inspection: No plumbing shall be covered, enclosed, or concealed before inspection and approval (see §105).
Prohibited vs. Required Practices
| Practice | Status |
|---|---|
| Running threads on drainage pipe | ❌ Prohibited |
| Full-bore cleanout access at direction changes | ✅ Required |
| Using 90° standard elbow for horizontal-to-horizontal change | ❌ Prohibited |
| Concealing pipe before inspection | ❌ Prohibited |
| Approved fittings for all direction changes | ✅ Required |
| Trap for every fixture | ✅ Required |
| Mixing storm and sanitary in separate systems | ❌ Prohibited |
§306
Location
NPC 2000 · Chapter 3 · Section 306
Code Requirement
306.1
Plumbing systems shall be located so as to be accessible for inspection, repair, and replacement without requiring the removal of permanent construction.
306.2
Water service pipes shall be laid at sufficient depth to be protected from frost where applicable, and from physical damage. In Philippine conditions, a minimum cover of 300 mm is typical for service pipes.
306.3
Water supply pipes shall be separated from drainage pipes by a minimum horizontal distance of 300 mm where running parallel in the same trench — or installed in separate trenches.
Minimum Separation / Cover
Water pipe in trench (cover)≥ 300 mm
Water from drain (parallel trench)≥ 300 mm H
Building sewer cover (vehicular)≥ 600 mm
§307
Connections to Plumbing System Required
NPC 2000 · Chapter 3 · Section 307
Code Requirement
307.1
Every plumbing fixture, drain, appliance, and appurtenance that receives or discharges liquid wastes shall be properly connected to the drainage system of the building.
307.2
No fixture shall drain into a storm drain, gutter, yard, or surface without being properly piped and connected to the approved sanitary drainage system.
307.3
Equipment that discharges indirectly (food equipment, sterilizers, ice machines) must connect through an air gap or air break to a receptor connected to the drain — never directly to the sanitary drain.
§308
Sewers Required
NPC 2000 · Chapter 3 · Section 308
Code Requirement
308.1
Where a public sewer is available within 30 m (100 ft) of the property line, every building intended for human occupancy shall connect its building sewer to the public sewer.
308.2
Where a public sewer is not available, the building shall be served by an approved private sewage disposal system (septic tank with absorption field) as specified in Chapter 10.
308.3
Storm water and sanitary sewage shall be kept separate and distinct where the public system is a separate system. No storm water shall be admitted to sanitary sewers.
Sewer Connection Rule
Public sewer within30 m of lot
→ Connect toPublic sewer
No public sewer→ Septic (Ch. 10)
§309
Grade of Horizontal Drainage Piping
NPC 2000 · Chapter 3 · Section 309 · ★ Exam Essential
Code Requirement
309.1
Horizontal drainage pipes shall be run in practical alignment and a uniform grade of not less than ¼ inch per foot (2%) toward the point of disposal for pipes of 3 inches (75 mm) or smaller diameter.
309.2
Drainage pipes of 4 inches (100 mm) or larger diameter shall have a minimum grade of ⅛ inch per foot (1%) toward the point of disposal.
309.3
Where it is impractical to obtain a proper grade due to structural conditions, the Administrative Authority may approve a lesser grade, provided adequate velocity is maintained. Minimum velocity is 0.6 m/s (2 fps) self-cleansing velocity.
Grade Requirements
Pipe ≤ 75 mm (3 in)Min 2% grade
Pipe ≥ 100 mm (4 in)Min 1% grade
2% = ¼" per ft20 mm per m
1% = ⅛" per ft10 mm per m
Min self-clean velocity0.6 m/s
Pipe Grade Diagram — §309
Practical Grade Reference Table
| Pipe Size | Min Grade | Drop per 1 m | Drop per 3 m | Equivalent |
|---|---|---|---|---|
| 50 mm (2 in) | 2% | 20 mm | 60 mm | ¼ in / ft |
| 75 mm (3 in) | 2% | 20 mm | 60 mm | ¼ in / ft |
| 100 mm (4 in) | 1% | 10 mm | 30 mm | ⅛ in / ft |
| 150 mm (6 in) | 1% | 10 mm | 30 mm | ⅛ in / ft |
| 200 mm (8 in) | 1% | 10 mm | 30 mm | ⅛ in / ft |
Image needed — [CH3-DIAGRAM-A]: Rendered isometric view of a building's horizontal drain branch showing both 2% and 1% grades with dimension triangles, pipe size callouts, and a level reference line.
§310
Changes in Direction of Drainage Flow
NPC 2000 · Chapter 3 · Section 310 · ★ Exam Essential
Code Requirement
310.1
Changes in direction of drainage flow shall be made by the use of appropriate drainage fittings only.
310.2
Horizontal to Vertical: Use wye (Y), combination Y and ⅛ bend, or sanitary tee (T) branches for waste only.
310.3
Vertical to Horizontal: Use long-sweep ¼ bend, combination Y and ⅛ bend, or approved offsets. Standard (short-sweep) 90° bends are NOT permitted for this transition.
310.4
Horizontal to Horizontal: Use 45° wye, combination Y and ⅛ bend, or long-sweep ¼ bend only. Standard tees and 90° elbows are NOT permitted for horizontal-to-horizontal changes.
Approved Fittings Summary
Horiz → VerticalWye, San. T
Vertical → HorizLong-sweep ¼ bend
Horiz → Horiz45° Wye, L-sweep
Any directionY + ⅛ combo
Approved vs. Prohibited Fittings — §310
Approved fitting
Prohibited fitting
Key dimension
Image needed — [CH3-DIAGRAM-B]: Rendered isometric or plan-view drawing of a complete drain branch showing 45° wye entry, long-sweep bends, and sanitary tee — with "prohibited" alternatives shown in red for comparison.
§311
Separate Sewer for Each Building
NPC 2000 · Chapter 3 · Section 311
Code Requirement
311.1
Every building shall be provided with a separate building sewer connecting to the public sewer. No building shall be permitted to connect its drainage system to that of another building.
311.2
Exception: Where multiple buildings are on the same lot or under single ownership, a common building sewer may be permitted by the Administrative Authority, provided it is of adequate size.
This rule prevents one building's drainage problem (blockage, surcharge) from affecting neighboring buildings.
§312
Rodent Proofing
NPC 2000 · Chapter 3 · Section 312
Code Requirement
312.1
All openings in floors, walls, or ceilings through which pipes pass shall be closed with non-corrosive material (metal escutcheon, sheet metal, or mortar) to prevent rodent entry.
312.2
Openings around pipes passing through a floor within 150 mm (6 in) of a wall must also be sealed — they present a rodent pathway along both the wall and the floor surface.
312.3
All drain openings at floor or receptor level shall be provided with approved strainers or gratings with a minimum free-open area equal to the pipe cross-section.
312.4
Traps shall be maintained with a water seal at all times. A dry trap allows sewer gases and rodents to pass through. Floor drains in infrequently used areas shall be fitted with trap primers or trap guards.
Rodent Proofing Details
Pipe penetration sealNon-corrosive
Close-to-wall distanceWithin 150 mm
Floor drain strainerRequired
Trap seal maintainedAlways
Pipe Penetration Detail — §312
Image needed — [CH3-DIAGRAM-C]: Rendered cross-section showing pipe through floor with properly sealed collar (non-corrosive), floor strainer, and a trap with water seal — labeled with the 150mm rule for wall-adjacent pipes.
§313
Condemned Plumbing
NPC 2000 · Chapter 3 · Section 313
Code Requirement
313.1
Any plumbing installation found by the Administrative Authority to be unsafe, insanitary, or defective shall be condemned. The owner shall be notified in writing and required to remedy the defect within a specified time.
313.2
Condemned plumbing that is an immediate hazard to life or property may be disconnected and sealed by the Administrative Authority without prior notice.
313.3
Condemned plumbing shall not be reconnected to any utility or building system until it has been repaired, brought up to Code, and re-inspected and approved.
Written Notice to Owner
Set Deadline for Correction
Immediate Disconnect if Hazard
Re-inspection Required
§314
Piping Materials, Standards & Weights
NPC 2000 · Chapter 3 · Section 314 · ★ Exam Essential
Code Requirement
314.1
All piping materials shall conform to the specifications in this section and to the referenced standards. Materials not listed here require approval under §107 (Equivalency).
314.2
The material used shall be appropriate for the service: potable water supply pipes must be suitable for drinking water; drain-waste-vent (DWV) pipes must resist sewage and corrosive waste; gas pipes must be approved for gas service.
314.3
Dissimilar metals in contact with each other (e.g., copper and galvanized steel) shall be separated by dielectric unions or approved insulating fittings to prevent galvanic corrosion.
Key Rules
Soil pipe min. size100 mm
Copper: water supplyTypes K, L, M
PVC for cold waterS1000, S900
Dissimilar metalsDielectric union
Approved Pipe Materials — Water Supply
| Material | Standard | Use | Notes |
|---|---|---|---|
| Copper Tube (K, L) | ASTM B88 | Hot & cold supply | Best for potable water; K=heaviest, L=standard |
| Copper Tube (M) | ASTM B88 | Cold supply only | Lighter wall; not for concealed hot water |
| Galvanized Steel | ASTM A53 | Cold water supply | Not for hot — degrades faster; avoid for new work |
| PVC Pipe (S1000) | PNS 65 | Cold water supply | Most common in PH residential; not for hot water |
| PE (Polyethylene) | PNS / ASTM | Cold supply, underground | Flexible; used for service lines from meter |
| CPVC | ASTM D2846 | Hot & cold | Chlorinated PVC; rated for hot water service |
Approved Pipe Materials — Drain, Waste & Vent (DWV)
| Material | Standard | Typical Use | Notes |
|---|---|---|---|
| Cast Iron (hub-and-spigot) | ASTM A74 | All DWV, underground | Long service life; heavy; traditional choice |
| Cast Iron (no-hub) | ASTM A888 | All DWV, aboveground | Lighter installation; coupled with neoprene & clamp |
| PVC-DWV | ASTM D2665 / PNS | All DWV | Most common in PH; lightweight, easy to install |
| ABS-DWV | ASTM D2661 | All DWV | Black plastic; less common in Philippines |
| Galvanized Wrought Iron | ASTM A120 | Waste (not soil) | Legacy material; not for WC connections |
| Lead Pipe | FS WW-P-325 | P-trap connections only | Now largely replaced by PVC traps |
| Vitrified Clay | ASTM C700 | Building sewer (underground) | For sewer from building to street only |
Image needed — [CH3-DIAGRAM-D]: Visual comparison chart of pipe cross-sections — cast iron, PVC, copper, galvanized — with nominal vs. actual ID/OD callouts, wall thickness, and typical application icons.
Diagram Requests — Chapter 3
Images Needed for This Chapter
[CH3-DIAGRAM-A] §309 — Isometric view of a horizontal drain branch. Show both a ≤75mm pipe at 2% and a ≥100mm pipe at 1%. Include a level reference line, dimension triangles showing drop per meter, and flow direction arrows.
[CH3-DIAGRAM-B] §310 — Plan + isometric view of a drain branch junction. Show approved (45° wye, long-sweep 90°, combo Y+⅛) in green and prohibited (standard tee, short 90°, S-trap) in red. Label each fitting type.
[CH3-DIAGRAM-C] §312 — Cross-section detail of pipe through concrete floor. Show: metal escutcheon/collar around pipe, sealed gap between pipe and slab, 150mm wall rule, floor drain strainer, and trap water seal below.
[CH3-DIAGRAM-D] §314 — Pipe material comparison: cross-section circles for cast iron, PVC-DWV, copper Type L, and galvanized steel. Label each with: nominal size, OD, ID, wall thickness, and primary use. Use navy/orange color scheme.