What is the minimum pipe diameter for domestic drainage?

100 mm is the minimum recommended diameter for building drainage.

What is the self-cleansing gradient for a 100 mm pipe?

A gradient of 1 in 60 is recommended for 100 mm pipes.

Where must manholes be located in a drainage layout?

At intersections of drains, and at every change of alignment, gradient, or diameter.

What is the maximum distance between manholes?

For small diameter pipes (up to 0.9 m), the maximum spacing is 30 meters.

IS 1742 Part 2

: 1972

Code of Practice for Drainage (Outside Buildings) - Part 2: Foul Water Drains

CurrentFrequently UsedCode of PracticeBIMMEP · Drainage, Sewerage and Sanitary Fittings

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This code provides comprehensive guidelines for the design, layout, construction, and maintenance of foul water building drainage systems. It establishes standard practices for pipe sizing, determining gradients to maintain self-cleansing velocities, and the proper placement of manholes and inspection chambers.

Provides guidance on the design and construction of foul water drainage systems outside buildings.

Quick Reference Values

Minimum diameter of domestic drain pipe100 mm

Minimum diameter of public sewer150 mm

Gradient for 100 mm diameter pipe1 in 60

Gradient for 150 mm diameter pipe1 in 100

Maximum manhole spacing for pipes up to 0.9m diameter30 m

Minimum concrete cover for pipes under roads150 mm all around

Practical Notes

Drains should strictly not pass under a building. If unavoidable, use cast iron pipes with mechanical joints or completely encase the pipe in reinforced concrete.

Always provide a manhole or inspection chamber at every change of alignment, gradient, or diameter.

Ensure pipes are laid to appropriate gradients to maintain self-cleansing velocities and prevent siltation.