What is the minimum slope for a 100mm horizontal drain pipe?

A gradient of 1 in 40 is recommended, but flatter gradients up to 1 in 80 may be used in specific cases (Clause 5.3.3).

What is the minimum water seal depth for a trap?

50 mm for most fixtures. For traps not in constant use, such as floor traps, the seal should be at least 75 mm to account for evaporation (Clause 6.3).

What is the purpose of a vent pipe?

To prevent loss of water seals in traps due to siphonage or back-pressure, and to ventilate the system by allowing foul air to escape at a high level (Clause 9.1).

How is a new sanitary pipework system tested?

Either with a water test (filled to a head of at least 3m for 10 mins with no leakage) or a smoke test (pressurized to 38 mm water gauge for 15 mins) (Clause 13).

IS 5329

: 1983

Code of practice for sanitary pipe work above ground for buildings

CurrentFrequently UsedCode of PracticeBIMMEP · Public Health Engineering

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This code of practice provides guidelines for the design, layout, and installation of sanitary pipework for drainage of soil and waste from buildings. It covers materials, pipe sizing based on discharge units, trapping, ventilation, and testing of above-ground systems. The standard aims to ensure efficient and hygienic removal of wastewater without nuisance from foul air.

Code of practice for sanitary pipe work above ground for buildings

Quick Reference Values

Minimum trap water seal depth50 mm

Minimum trap water seal for floor traps75 mm

Typical gradient for 100 mm drains1 in 40

Minimum diameter of soil stack for WCs100 mm

Minimum water test head for stacks3 m

Discharge Unit (DU) for a wash basin1.5 DU

Discharge Unit (DU) for a WC (>6.5L flush)4 DU

Practical Notes

The code covers both one-pipe and two-pipe systems. The choice depends on building type and complexity, with the one-pipe system being more common in modern residential buildings.

Proper installation of anti-siphonage pipes is critical to prevent the loss of trap water seals, which is a common cause of foul smells entering the building.

Close coordination with architectural and structural drawings is essential to ensure required pipe slopes can be achieved without clashes and with adequate access for maintenance.