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IS 1742:1972 Part 2 is the Indian Standard (BIS) for drainage (outside buildings) - part 2: foul water drains. 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.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
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.
stoneware pipescast iron pipesconcrete pipesuPVC pipes
International Equivalents
Similar International Standards
BS EN 752:2017BSI (UK) / CEN (Europe)
HighCurrent
Drain and sewer systems outside buildings - Sewer system management
Covers planning, hydraulic design, construction, and maintenance of all drainage systems outside buildings.
ASCE MOP 77ASCE (US)
HighCurrent
Design and Construction of Sanitary and Storm Sewers
Provides comprehensive guidance on the design and construction of storm sewer systems.
AS/NZS 3500.3:2021Standards Australia / Standards New Zealand
HighCurrent
Plumbing and drainage, Part 3: Stormwater drainage
Details requirements for materials, design, and installation of stormwater drainage systems.
BS 8005BSI (UK)
MediumWithdrawn
Sewerage. Guide to new sewerage construction
Was the primary UK code for sewer construction and a contemporary of IS 1742.
Key Differences
≠IS 1742 is highly prescriptive (e.g., specifying materials like brickwork and fixed gradients), whereas modern standards like BS EN 752 are performance-based, focusing on achieving functional requirements (e.g., self-cleansing velocity) with a wide range of materials and design approaches.
≠Modern international standards extensively cover plastic materials (PVC, HDPE, GRP) and advanced jointing systems. IS 1742 (from 1972) focuses on traditional materials like concrete, stoneware, and brick masonry, with limited mention of modern alternatives.
≠International codes incorporate sophisticated hydraulic modeling inputs, including detailed rainfall intensity-duration-frequency (IDF) data and climate change considerations. IS 1742's guidance on rainfall calculation is comparatively simplistic.
≠Modern standards like AS/NZS 3500.3 and BS EN 752 integrate concepts of Sustainable Urban Drainage Systems (SUDS) / Water Sensitive Urban Design (WSUD), such as infiltration and detention. IS 1742 focuses purely on conveyance of water away from the site.
Key Similarities
≈All standards are based on fundamental principles of gravity flow for conveying surface water.
≈The use of the Manning's formula for calculating the flow capacity of pipes and channels is a common hydraulic design basis across all the standards.
≈The core concept of maintaining a minimum 'self-cleansing velocity' to prevent siltation and blockages is a fundamental requirement in both IS 1742 and its international counterparts, although the specific values may differ.
≈The basic functional components of the drainage system, such as drains/pipes, manholes/inspection chambers, and gullies/inlets, are conceptually similar across all standards.
Parameter Comparison
Parameter
IS Value
International
Source
Minimum Self-Cleansing Velocity (Pipes)
0.6 m/s (for drains up to 300 mm diameter)
0.75 m/s (for storm sewers at design flow)
BS EN 752
Minimum Gradient Approach
Prescribes minimum gradients based on pipe size (e.g., 1 in 120 for 150mm pipe).
Performance-based: Gradient is calculated to achieve the required self-cleansing velocity.
ASCE MOP 77 / BS EN 752
Minimum Pipe Diameter (Main Line)
150 mm
200 mm (8 inches) often recommended for public storm sewers to minimize blockages.
ASCE MOP 77
Manning's 'n' (Smooth Concrete Pipe)
0.015
0.013 (for modern precast concrete)
ASCE MOP 77
Maximum Manhole Spacing (e.g., 200-300mm pipe)
30 metres
Up to 90-120 metres, depending on access for modern cleaning equipment (jetting/CCTV).
BS EN 752
Design Storm Return Period (Urban)
Not explicitly defined, often taken as 2-5 years in practice.
Typically 1-in-20 to 1-in-30 years for no surcharge, with flood routing checks for 1-in-100 years.
BS EN 752
⚠ Verify details from original standards before use
Key Values6
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
Tables & Referenced Sections
Key Tables
Table 1 - Minimum gradients for different sizes of pipes