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IS 17429:2020 Part 2 is the Indian Standard (BIS) for plumbing services - code of practice - part 2: drainage and sanitation. This code of practice provides detailed guidelines for the design, installation, and testing of drainage and sanitation systems within and around buildings. It covers material specifications, pipe sizing using the discharge unit method, trapping, ventilation systems (single stack, one-pipe, etc.), and commissioning tests to ensure a functional and hygienic system. This standard is a modern replacement for the drainage section of the National Building Code.
Covers general requirements, design, installation, and testing of drainage and sanitation systems in buildings.
Quick Reference — Top IS 17429 Part 2:2020 Values
Key values for drainage system design, including pipe gradients, fixture units, vent requirements, testing pressures, and installation clearances.
✓ Verified 2026-04-27
Reference
Value
Clause
Min. Gradient (Pipes ≤ 100 mm dia)— Recommended minimum gradient for soil and waste pipes.
1 in 40
Cl. 6.2.1
Min. Gradient (Pipes > 100 mm dia)— Recommended minimum gradient for soil and waste pipes.
1 in 80
Cl. 6.2.1
Min. Water Seal Depth (General)— For most internal traps like floor traps (nahani traps).
50 mm
Cl. 7.2.2
Min. Water Seal Depth (Exposed Traps)— For traps exposed to sun/wind to account for evaporation.
75 mm
Cl. 7.2.2
Fixture Unit (FU) - Water Closet— For a typical 6-litre flush cistern.
4 FU
Table 4
Fixture Unit (FU) - Wash Basin— Standard value for a single wash basin.
1 FU
Table 4
Fixture Unit (FU) - Kitchen Sink— Standard value for a domestic kitchen sink.
2 FU
Table 4
Max. FU on 100 mm Vertical Stack— Maximum discharge unit loading for a single vertical stack.
240 FU
Table 6
Min. Diameter of Main Vent Pipe— Or 1/2 the diameter of the soil pipe, whichever is greater.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! The concept of Discharge Units (DU) is fundamental for sizing pipes; accurately calculating the total DU load for a branch or stack is critical to avoid under-sizing.
! Proper venting is often overlooked but is crucial to prevent trap siphonage, back pressure, and foul gas entry into the building. Clause 8 provides detailed options.
! This standard should be read in conjunction with IS 17429 (Part 1) for water supply to have a complete understanding of the building's plumbing services.
Comprehensive code for the design, installation, and maintenance of plumbing systems, including water supply.
BS EN 806 (Parts 1-5)British Standards Institution / CEN, UK / Europe
HighCurrent
Specification for installations inside buildings conveying water for human consumption
Multi-part standard covering general specifications, design, pipe sizing, installation, and operation for in-building water systems.
AS/NZS 3500.1:2021Standards Australia / Standards New Zealand, Australia / New Zealand
HighCurrent
Plumbing and drainage, Part 1: Water services
Specifies requirements for the design, installation, and commissioning of water services from the point of connection to the points of discharge.
UPC 2021International Association of Plumbing and Mechanical Officials (IAPMO), USA
HighCurrent
Uniform Plumbing Code
A model code providing requirements for the installation and inspection of plumbing systems, including water supply.
Key Differences
≠Pipe sizing in IS 17429 uses a 'Loading Unit' (LU) method adapted for Indian conditions, whereas the US-based IPC and UPC predominantly use a 'Water Supply Fixture Unit' (WSFU) method. While conceptually similar, the unit values and resulting pipe sizes can differ.
≠IS 17429 specifies material compliance by referencing Indian Standards (e.g., IS 4984 for PE pipes, IS 15778 for CPVC pipes). International codes reference their respective national or regional standards (e.g., ASTM, NSF for IPC; EN for BS EN 806).
≠The classification of fluid hazard levels for backflow prevention in IS 17429 (Fluid Categories 1 to 5, based on the European model) differs from the IPC's hazard classification (high vs. low hazard), which can lead to different requirements for backflow prevention devices in similar situations.
≠IS 17429 mandates a minimum hydrostatic test pressure of 10 bar (1 MPa) or 1.5 times the working pressure, whichever is greater. The IPC requires testing at 1.5 times the working pressure but not less than 100 psi (0.69 MPa), a lower minimum threshold.
Key Similarities
≈All standards have the fundamental objective of protecting public health by preventing contamination of potable water through cross-connections, back-siphonage, and back-pressure, making backflow prevention a core principle.
≈All codes mandate requirements for hot water systems to both prevent Legionella growth (through adequate storage temperatures, typically ≥60°C) and protect users from scalding (through temperature limitation at outlets, typically ≤50-55°C).
≈IS 17429 and its international counterparts all incorporate provisions for water conservation, specifying maximum flow rates for fixtures like faucets, showerheads, and toilets.
≈All standards share common principles for system installation, including requirements for proper pipe support and spacing, installation of isolation valves for maintenance, and protection of pipes from physical damage and freezing.
≈The underlying hydraulic principle of using diversity/simultaneity factors to calculate peak demand is common to all codes, acknowledging that not all fixtures will be used at once in a multi-fixture system.
Parameter Comparison
Parameter
IS Value
International
Source
Hydrostatic Leak Test Pressure (Minimum)
1.5 x working pressure, but not less than 10 bar (1 MPa)
1.5 x working pressure, but not less than 100 psi (0.69 MPa)
IPC 2021
Maximum Recommended Water Velocity (Cold Water)
1.5 - 2.5 m/s
8 ft/s (~2.4 m/s)
IPC 2021 (Common design practice based on Chapter 6 and Appendix E)
Minimum Air Gap for Backflow Prevention
2 x inlet pipe diameter, but not less than 20 mm (for DN15 tap)
2 x inlet pipe diameter, but not less than 1 inch (25.4 mm)
IPC 2021
Maximum Hot Water Temperature at Fixture Outlet (Safety)
Recommended not to exceed 55°C
Maximum 120°F (49°C) for public-use lavatories
IPC 2021
Minimum Hot Water Storage Temperature (Legionella Control)
≥ 60°C
≥ 60°C (140°F)
BS EN 806-2
Maximum Flow Rate (Private Lavatory Faucet)
6 L/min (Desirable)
1.5 gpm (5.7 L/min)
IPC 2021 (Referencing EPA WaterSense)
Minimum Dynamic Pressure at Shower Outlet
70 kPa (0.7 bar)
50 kPa (0.5 bar) for a simplified system
BS EN 806-3
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Minimum trap water seal for WC50 mm
Minimum diameter for a soil pipe serving one or more WCs100 mm
Recommended minimum gradient for 100 mm drain1 in 80
Maximum spacing of manholes on straight run (up to 300mm dia drain)30 m
Air test pressure for drainage system100 mm water gauge for 5 minutes
Minimum diameter of main ventilating pipe50 mm
Key Formulas
Pipe Sizing based on Discharge Units (DU) from Table 4 and Table 7
Tables & Referenced Sections
Key Tables
Table 2 - Minimum Water Seal Depth for Traps
Table 3 - Minimum Diameter of Sanitary Appliances and Traps
Table 4 - Discharge Units for Sanitary Appliances
Table 6 - Minimum Gradients for Drains
Table 7 - Maximum Number of Discharge Units to be Connected to Stacks
Table 11 - Spacing of Manholes
Key Clauses
Clause 6 - Traps
Clause 7 - Sanitary Pipework
Clause 8 - Ventilation of Drainage System
Clause 9 - Layout of Drains in Buildings and Houses
What is the minimum recommended slope for a 100mm house drain?+
A gradient of 1 in 80 is recommended, though 1 in 100 is permissible for pipes with smooth internal surfaces like uPVC. (Table 6)
What is a 'Discharge Unit' (DU) and why is it important?+
It's a value assigned to a plumbing fixture representing its likely load on the drainage system. Summing up DUs is the standard method for sizing pipes and stacks. (Clause 3.16 & Table 4)
What is the minimum water seal depth for a WC trap?+
50 mm. A sufficient seal depth is essential to prevent sewer gases from entering the building. (Table 2)
How is a newly installed drainage system tested?+
It can be tested with either an air test (at 100 mm water gauge pressure) or a water test. The test verifies that the joints are leak-proof. (Clause 10.2)