Code of practice for building drainage

The scope of IS 1742 covers estimation of maximum flow of domestic sewage and sizing of drainage pipes based on fixture units. Key specifications include:

• Fixture Unit Values (Clause 4.5.1, Table 1): Assigns load factors to sanitary fixtures, e.g., tank water closet = 6, flush-valve water closet = 8, kitchen sink = 2.

• Fixture Unit Values by Drain/Trap Size (Clause 4.5.1.1, Table 2): For example, 30 mm drain = 1 unit, 100 mm drain = 6 units.

• Maximum Fixture Units per Pipe Diameter (Clause 5.1.4, Table 3): Limits fixture units connected to branches and stacks, e.g., 50 mm pipe can serve 6 units on a horizontal branch.

• Maximum Fixture Units for Building Drains and Sewers (Clause 4.5.1.4, Table 4): Depends on pipe diameter and gradient, e.g., 150 mm pipe at 1/100 gradient can serve 700 units.

These tables and clauses define the scope for designing domestic sewage systems per IS 1742.

Sources: Clause 4.5.1, Clause 4.5.1.1, Clause 5.1.4, Clause 4.5.1.4

As per Clause 2.0 of IS 1742, definitions are provided for terms used in the standard to ensure clarity. Key specifications related to fixture units and sewage flow estimation are given in the following tables:

TABLE 1: Fixture Units for Different Sanitary Appliances (Clause 4.5.1)

*Note: A shower head over a bath tub does not increase the fixture value.

TABLE 2: Fixture Unit Values Based on Fixture Drain or Trap Size (Clause 4.5.1.1)

TABLE 3: Maximum Number of Fixture Units Connected to Branches and Stacks (Clause 4.5.1.4)

TABLE 4: Maximum Number of Fixture Units Connected to Building Drains and Sewers (Clause 4.5.1.4)

These tables provide essential data for estimating sewage flow and designing drainage systems based on fixture types, sizes, and pipe diameters.

Sources: Clause 2.0, Clause 4.5.1, Clause 4.5.1.1, Clause 4.5.1.4

As per IS 1742 Clause 3.1, all materials and fittings must conform to the latest relevant Indian Standards or be of best quality if no standard exists. Key tables for design and specification include:

Table 1: Fixture Units for Different Sanitary Appliances (Clause 4.5.1)

Table 2: Fixture Unit Values Based on Drain or Trap Size (Clause 4.5.1.1)

Table 3: Maximum Number of Fixture Units Connected to Branches and Stacks (Clause 4.5.1.4)

Table 4: Maximum Number of Fixture Units Connected to Building Drains and Sewers at Various Gradients (Clause 4.5.1.4)

These tables and specifications guide the selection of pipe sizes, fixture units, and materials for sanitary installations ensuring compliance with IS 1742 standards.

Sources: Clause 3.1, Clause 4.5.1, Clause 4.5.1.1, Clause 4.5.1.4

Design considerations in IS 1742 emphasize thorough preliminary data collection before designing drainage systems, including site plans, building plans, usage description, sewer availability, local bye-laws, sewage nature, cover depth, subsoil conditions, location of other services, surface reinstatement, traffic control, wayleaves, and damage assessment (Clause 4.2). Key tables for design include:

Table 1: Fixture Units for Different Sanitary Appliances (Clause 4.5.1)

Table 3: Maximum Number of Fixture Units Connected to Branches and Stacks (Clause 4.5.1.4)

Table 4: Maximum Number of Fixture Units Connected to Building Drains and Sewers by Gradient (Clause 4.5.1.4)

These tables assist in estimating peak sewage flow and sizing pipes accordingly. The design must also consider subsoil conditions, traffic loads, and local regulations as per Clause 4.2.

Sources: Clause 4.2, Clause 4.5.1, Clause 4.5.1.4

For Installation Practices in IS 1742, key specifications and tables include:

• Clause 3.1 mandates all materials and fittings must conform to the latest relevant Indian Standards or be of best quality if no standard exists.

• Maximum Fixture Units (FU) connected to pipes (Clause 4.5.1.4, Table 3):

• Maximum Fixture Units for Building Drains and Sewers (Clause 4.5.1.4, Table 4) based on pipe diameter and gradient:

• Rainwater Pipe Sizing for Roof Drainage (Clause 4.10.3.9, Table 5):

• Storm water must be discharged into suitable open drains constructed in pucca masonry at changes in direction or gradient (Clause 4.10.3.9).

These tables and clauses guide proper sizing and installation to ensure efficient drainage and compliance with IS 1742.

Sources: Clause 3.1, Clause 4.5.1.4, Table 3, Table 4, Clause 4.10.3.9, Table 5

As per Clause 4.10.3.8 of IS 1742, rain-water pipes for roof drainage shall be sized based on roof area using Table 5. A bell mouth inlet at the roof surface improves drainage if proper slopes are provided. Pipes are typically spaced about 6 m apart, considering window and arch positions. The strainer area should be 1 to 2 times the pipe cross-sectional area.

Table 5: Sizing of Rain-Water Pipes for Roof Drainage (Roof area in m² vs. Average rainfall in mm/h)

As per Clause 6.2, storm water should be led off in a suitable open drain, constructed in pucca masonry at changes in direction or gradient.

This ensures proper sizing and installation of rain-water pipes for effective roof drainage.

Sources: Clause 4.10.3.8, Clause 6.2, Table 5

Key specifications for backfilling and protection of pipes per IS 1742 are:

• Bedding (Clause 5.9.1):

  • Bedding shall be rectangular, extending laterally at least 150 mm beyond both sides of the pipe barrel projection.
  • Concrete thickness below the pipe barrel: minimum 100 mm for pipes under 150 mm diameter, and 150 mm for pipes 150 mm and above.
  • Concrete bed forms a cradle up to the invert level to avoid line contact.

• Dimensions for Bedding and Haunching:

• Backfilling (Clause 5.14.3 & 5.14.4):

  • First fill: hand-pack selected fine material around the lower half of the pipe to buttress it.
  • Continue filling to 150 mm above pipe top with fine material, watered and rammed evenly on both sides to maintain equal pressure.
  • No tipping of material until first 150 mm of filling is complete.

• Haunching (Clause 5.9.1):

  • Concrete bed carried up to horizontal diameter level.
  • Splays from this level carried up on both sides to meet pipe barrel tangentially.

These ensure pipe stability and protection during backfilling operations.

Sources: Clause 5.9.1, Clause 5.14.3, Clause 5.14.4

IS 1742 specifies that all materials and fittings used must conform to the latest relevant Indian Standards and are subject to inspection at the manufacturer's works before dispatch, ensuring quality and workmanship as per Clause 3.1. For testing, the code mandates rounding off test results according to IS 2-1960, maintaining the same number of significant figures as the specified values (Clause 0.4). A specific test mentioned is the Water Test (Clause 8.2.3), which is essential for verifying the integrity of the system. Additionally, French drains construction involves excavation with graded filling materials to ensure proper drainage (Clause 7.1.2). These provisions collectively ensure thorough inspection and testing protocols for compliance and quality assurance.

Sources: Clause 0.4, Clause 3.1, Clause 7.1.2, Clause 8.2.3

As per IS 1742 Clause 9.2.2, maintenance and cleaning of drainage systems include the following key operations:

• Remove covers of inspection chambers and manholes; scrub side benchings and channels.
• Clean and flush intercepting traps with clean water, ensuring the stopper in the rodding arm is securely replaced.
• Remove covers/access plates of gullies; plunge and flush traps thoroughly without flushing gully deposits into the system.
• Repair any defects found during inspection or testing.
• Replace covers of inspection chambers and gullies, bedding them in suitable grease or other materials.
• Paint ladders/rings in deep manholes and external manhole covers with approved paints.

Additionally, Clause 9.4 mandates periodic examination of subsoil drains for obstructions such as roots.

For estimating maximum flow of domestic sewage, Clause 4.5.1 provides fixture unit values for various sanitary appliances as load factors, for example:

These fixture units help in designing and maintaining drainage capacity.

Sources: Clause 9.2.2, Clause 9.4, Clause 4.5.1

Key safety and precautionary measures for sewer maintenance crews per IS 1742 Clause 9.2.1 include:

• No smoking or open flames; guard against sparks.
• Erect warning signs and use only safety gas-proof electric lighting.
• Test atmosphere for noxious gases and oxygen deficiency before entry.
• If atmosphere is safe, enter with safety belt and two men at top; repeat gas tests frequently for extended jobs.
• If hazardous gases or oxygen deficiency exist and ventilation is impractical, wear hose masks, use permissible safety lights, rubber boots or non-sparking shoes, and non-sparking tools.
• Check ladder rungs carefully before use; have at least two men for emergency lifting.
• Use portable air blowers of weatherproof and flameproof types placed at least 2 m from openings on the leeward side for forced ventilation. Diesel motors without sparking plugs are permitted.

Additionally, Clause 3.1 mandates all materials and fittings conform to latest relevant Indian Standards or be of best quality if no standard exists.

These precautions ensure worker safety in hazardous sewer environments and compliance with IS 1742 requirements.

Sources: Clause 9.2.1, Clause 3.1

As per IS 1742, Clause 4.10.5, surface water disposal methods include several options (4.10.5.1 to 4.10.5.5), with preference given to the method in 4.10.5.1. Clause 4.2.4 emphasizes that disposal of surface and subsoil water should consider local conditions, including flood levels and authority requirements, with natural water courses or soakaways used if permissible. Clause 4.2.3 and 4.2.3.3 specify that other sewage disposal methods must comply with local water supply authority regulations to prevent pollution, especially for subsoil dispersion. Although exact formulas or tables are not provided in the retrieved context, the code stresses adherence to tolerance limits for sewage effluents and proper sampling/testing methods as per relevant standards. For detailed disposal design, consult the specific sub-clauses 4.10.5.1 to 4.10.5.5 and local authority guidelines.

Sources: Clause 4.10.5, Clause 4.2.3, Clause 4.2.4, Clause 4.2.3.3

IS 1742 addresses subsoil drainage primarily in Clauses 7.1 and 4.11. Subsoil drains are designed to remove water from soil to prevent structural damage. Key points include:

• Clause 7.1 defines subsoil drains as systems to collect and remove water from soil beneath structures.
• Clause 4.11 details subsoil water drainage principles, emphasizing the need to prevent water pressure buildup.
• Clause 4.11.4 describes systems of subsoil drainage, typically involving perforated pipes laid in gravel trenches to collect water.
• Clause 2.41 defines drainage systems broadly, including subsoil drainage.

Typical design involves:

• Perforated pipes with a minimum diameter (often 100 mm or more).
• Gravel or coarse aggregate surrounds to facilitate water flow.
• Proper gradient (usually 1 in 100 to 1 in 200) to ensure flow.

Unfortunately, the retrieved context does not include explicit formulas or tables. For detailed design, refer to IS 1742 Clauses 7.1 and 4.11 for specifications on pipe size, gradient, and materials.

Sources: Clause 7.1, Clause 4.11, Clause 4.11.4, Clause 2.41

As per IS 1742, key specifications for manholes and inspection chambers are:

• Minimum sizes: Circular chambers should have a minimum diameter of 1.4 m, and rectangular chambers should have minimum internal dimensions of 1.2 m x 0.9 m (Clause 1.4). These sizes should align with standard brick dimensions to avoid waste (Notes 1 and 2).

• Size adjustment: Chamber sizes must allow for necessary examination and clearance of drains, and be increased if more entries to the manhole exist (Clause 4.9.2).

• Location: Manholes or inspection chambers are required at every change of alignment, gradient, or diameter of a drain. Bends and junctions should be grouped in manholes where possible (Clause 4.9).

• Depth considerations: For manholes 1.5 m and above, detailed sectional plans and drop manhole designs are provided (Clause 1.5, Figures 4 and 5).

These provisions ensure accessibility, maintenance, and structural adequacy of manholes and inspection chambers.

Sources: Clause 1.4, Clause 4.9, Clause 4.9.2, Clause 1.5

IS 1742 provides key data for flow calculations and fixture units as follows:

1. Fixture Unit Values by Fixture Type (Clause 4.5.1, Table 1): | Type of Fixture | Fixture Unit Value | |----------------------------------------|--------------------| | Tank water closet | 6 | | Flush-valve water closet | 8 | | Bath tub | 3 | | Bidet | 3 | | Combination sink-and-tray (drain board)| 3 | | Drinking fountain | 1 | | Floor trap | 1 | | Kitchen sink, domestic | 2 | | Wash basin, ordinary | 1 | | Wash basin, surgeon's | 2 | | Shower stall, domestic | 2 | | Showers (group) per head | 3 | | Urinal wall lip | 4 | | Urinal stall | 4 | | Water closet, tank-operated | 4 | | Water closet, valve-operated | 8 |

2. Fixture Unit Values by Drain or Trap Size (Clause 4.5.1.1, Table 2): | Fixture Drain or Trap Size (mm) | Fixture Unit Value | |---------------------------------|--------------------| | 30 and smaller | 1 | | 40 | 2 | | 50 | 3 | | 65 | 4 | | 75 | 5 | | 100 | 6 |

3. Conversion of Total Fixture Units to Peak Flow (litres/min) is done using Fig. 1 curves (Clause 4.5.1.3), which differentiate systems predominantly with flush valves or flush tanks.

4. Maximum Number of Fixture Units per Pipe Diameter (Clause 4.5.1.4, Table 3): | Diameter (mm) | Max Fixture Units on Horizontal Branch | Max on Stack (3 storeys) | Max on Stack (>3 storeys) Total | Max at One Storey on Branch | |---------------|---------------------------------------|-------------------------|-------------------------------|-----------------------------| | 30 | 1 | 2 | 2 | 1 | | 40 | 3 | 4 | 8 | 2 | | 50 | 6 | 10 | 24 | 6 | | 65 | 12 | 20 | 42 | 9 | | 75 | 20 | 30 | 60 | 16 | | 100 | 160 | 240 | 500 | 90 | | 125 | 360 | 540 | 1100 | 200 | | 150 | 620 | 960 | 1900 | 350 | | 200 | 1400 | 2200 | 3600 | 600 | | 250 | - | 2500 | 3800 | 1000 | | 300 | 3900 | 6000 | 8400 | 1500 | | 375 | 7000 | - | - | - |

5. Maximum Fixture Units for Building Drains and Sewers by Pipe Diameter and Gradient (Clause 4.5.1.4, Table 4): | Diameter (mm) | Gradient 1/200 | 1/100 | 1/50 | 1/25 | |---------------|---------------|-------|-------|-------| | 100 | - | 180 | 216 | 250 | | 150 | - | 700 | 840 | 1000 | | 200 | 1400 | 1600 | 1920 | 2300 | | 250 | 2500 | 2900 | 3500 | 4200 | | 300 | 3900 | 4600 | 5600 | 6700 | | 375 | 7000 | 8300 | 10000 | 12000 |

These tables and curves enable estimation of peak sewage flow from fixture units and sizing of drainage pipes accordingly.

Sources: Clause 4.5.1, Clause 4.5.1.1, Clause 4.5.1.3, Clause 4.5.1.4

Key corrosion protection guidelines from IS 1742 include:

• Cast iron pipes are prone to severe external corrosion in soils permeated by peaty waters or with high sulphate content. Local experience must guide their use, and suitable protective measures should be applied if such soils are suspected (Clause 4.7.3.1).

• Protective coatings on cast iron pipes must be carefully inspected. Minor damages should be repaired by painting with hot tar or bitumen; major coating defects require recoating before use (Clause 8.1.3).

• All joints must be thoroughly water-tight by riveting, bolting, or soldering, with at least 50 mm overlap in gutters to prevent water ingress (Clause 6.1.2).

• For sizing rainwater pipes (important for corrosion prevention by ensuring proper drainage), refer to the following table from Clause 4.10.3.9:

These measures ensure durability and prevent corrosion by maintaining protective coatings and proper drainage.

Sources: Clause 4.7.3.1, Clause 8.1.3, Clause 6.1.2, Clause 4.10.3.9, TABLE 5 SIZING OF RAIN-WATER PIPES FOR ROOF DRAINAGE