হোম · নিরাপত্তা · BNBC 2006 · Part 8 · Chapter 7

BNBC 2006 · Part 8 — Building Services

Chapter 7 — Drainage and Sanitation

Superseded by BNBC 2020 (in force from 11 February 2021) — see note.

Sections in this chapter

7.1PURPOSE 7.2SCOPE 7.3TERMINOLOGY 7.4DRAINAGE AND SANITATION PLANS 7.5LICENSING OF PLUMBER 7.6DRAINAGE AND SANITATION REQUIREMENT 7.7MATERIALS AND APPLIANCES 7.8hangers and support and pipe jointing 7.9DESIGN CONSIDERATIONS 0.6or less 1.0or less 1.5or less 7.10DESIGN OF DRAINAGE AND SANITATION SYSTEM 7.11CONSTRUCTION RELATING TO CONVEYANCE OF RAINWATER AND SANITARY WASTES 7.12REFUSE CHUTE SYSTEM 7.13Health care drainage system 7.14INSPECTION, TESTING AND COMPLETION CERTIFICATE 7.15GUIDE TO MAINTENANCE

Drainage and Sanitation

7.1 PURPOSE

The purpose of this chapter is to set forth provisions for planning, design and installation of waste disposal systems in buildings.

7.2 SCOPE

7.2.1 This chapter specifies the general requirements for environmental sanitation for different categories of buildings according to their occupancy classification.

7.2.2 This chapter also covers the design, installation and maintenance of drainage systems together with all ancillary works such as manholes and inspection chambers used within the building and from the building to public sewers or to private waste disposal system (i.e. into septic tanks and seepage pits or subsurface drainage system).

7.2.3 The disposal of wastes from industries, nuclear plants, slaughter houses, etc. are not covered by this Code. These wastes shall be properly treated as specified by environmental quality standards of Bangladesh before their disposal into public sewers or into natural bodies of water.

7.3 TERMINOLOGY

This section provides an alphabetical list of all terms used and applicable to this chapter of the Code. In case of any conflict or contradiction between a definition given in this section and that in any other chapter or part of the Code, the meaning specified in this chapter shall govern for interpretation of the provisions of this chapter.

Bedding Factor : The ratio of the product of design load and factor of safety to the minimum crushing strength.

Branch : Any part of the piping system other than a main, riser, or stack.

Branch Interval : The length of soil or waste stack corresponding in general to a storey height, but in no case less than 2.5 m within which the horizontal branches from one floor or storey of building are connected to the stack.

Branch Vent : The vent connecting one or more individual vents with a vent stack or stack vent.

Building Drain : The building (house) drain is that part of the lowest piping or open channel of a drainage system which receives the discharges from soil, waste, and other drainage systems inside the walls of the building and conveys the same to the building (house) sewer, beginning at 0.9 m outside the building wall.

Building Sewer : The building (house) sewer is that part of the horizontal piping of a drainage system which extends from the end of the building drain and which receives the discharge of the building drain and conveys it to a public sewer, private sewer, individual sewage disposal system, or other point of disposal. Also known as SEWER.

Building Storm Drain : A building (house) storm drain is a building drain used for conveying rain water, surface water, ground water, subsurface water, condensate, cooling water, or other similar discharge to a building storm sewer or a combined sewer, extending to a part not less than 0.9 m outside the building wall. Also known as STORM DRAIN.

Drain : A drain is any pipe or open channel which carries waste water or waterborne wastes in a building drainage system.

Drainage System : A drainage system (drainage piping) includes all the piping within public or private premises, which conveys sewage, rain water, or other liquid wastes to a legal point of disposal, but does not include the mains of a public sewer system or a private or public sewage treatment or disposal plant.

DRINKING FOUNTAIN : A fountain or a tap raised from the floor with potable water supply connection.

Existing Work : The existing work is a plumbing system or any part thereof which was installed prior to the date of enforcement of this Code.

Fixture Unit : A fixture unit is a quantity in terms of which the load producing effects on the plumbing system of different kinds of plumbing fixtures are expressed on some arbitrarily chosen scale.

Flush Valves : A flush valve is a device located at the bottom of the tank for the purpose of flushing water closets and similar fixtures.

French Drain : A shallow trench filled with coarse rubble, clinker or similar material with or without field drain pipes.

Grade : The grade is the slope or fall of a line of pipe in reference to a horizontal plane. In drainage it is usually expressed as the fall in mm per m length of pipe.

Horizontal Branch : A horizontal branch is a drain pipe extending laterally from a soil or waste stack or building drain, with or without vertical sections or branches, which receives the discharge from one or more fixture drains and conducts it to the soil or waste stack or to the building (house) drain.

Horizontal Pipe : A horizontal pipe is any pipe or fitting which is installed in a horizontal position or which makes an angle of less than 45 degrees with the horizontal.

Individual Vent : An individual vent is a pipe installed to vent a fixture trap and which connects with the vent system above the fixture served or terminates in the open air.

Interceptor : An interceptor is a device designed and installed so as to separate and retain deleterious, hazardous, or undesirable matter from normal wastes and permit normal or liquid wastes to discharge into the disposal terminal by gravity.

Invert : The lowest point of the internal surface of a pipe or channel at any cross-section.

KITCHEN SINK : Sink or washing facilities raised above or at the level of the floor fitted with a tap.

Leader : A vertical drainage pipe that carries rainwater from roof or gutter drain to building storm drain or building drain or private disposal system.

Liquid Waste : The liquid waste is the discharge from any fixture, appliance, or appurtenance in connection with a plumbing system which does not receive faecal matter.

Load Factor : The load factor is the percentage of the total connected fixture unit flow rate which is likely to occur at any point in the drainage system. It varies with the type of occupancy, the total flow unit above the point being considered, and with the probability factor of simultaneous use.

Local Vent Stack : A vertical piping to which connections are made from the discharge side of traps and through which vapour or foul air is removed from the fixture or device used on bedpan washer.

Main : The main of any system of continuous piping is the principal artery of the system, to which branches may be connected.

Main Sewer : See Public Sewer.

Main Vent : The main vent is the principal artery of the venting system, to which vent branches may be connected.

Manhole : An opening by which a man may enter or leave a drain, a sewer or other closed structure for inspection, cleaning and other maintenance operations, fitted with a suitable cover.

Manhole Chamber : A chamber constructed on a drain or sewer so as to provide access thereto for inspection, testing or the clearance of obstruction.

Nonservice Latrine : A latrine other than service latrine.

Offset : An offset in a line of piping is a combination of elbows or bends which brings one section of the pipe out of line but into a line parallel with the other section.

Pipe System : The system to be adopted will depend on the type and planning of the building in which it is to be installed and will be one of the following:

a) Single Stack System (see Fig 8.7.1) : The one pipe system without trap ventilation pipe work.

b) One Pipe System (see Fig 8.7.2) : The plumbing system in which the waste from sinks, bath rooms and wash basins, and soil pipe branches are all collected into one main pipe connected directly to the drainage system. Gully traps and waste pipes are completely dispensed with but all the traps of water closets, basins, etc. are completely ventilated to preserve the water seal.

c) Two Pipe System (see Fig 8.7.3) : A discharge pipe system comprising two independent discharge pipes, one conveying soil directly to the drain, the other conveying waste water to the drain through a trapped gully. The system may also require ventilating pipes.

Plumbing : The plumbing includes the practice, materials, and fixtures used in the installation, maintenance, extension, and alteration of all piping, fixtures, appliances, and appurtenances in connection with any of the following : sanitary drainage or storm drainage facilities, the venting system and the public or private water supply systems, within or adjacent to any building, structure, or conveyance; also the practice and materials used in the installation, maintenance, extension, or alteration of the storm water, liquid waste, or sewerage, and water supply systems of any premises to their connection within any point of public disposal or other acceptable terminal.

Plumbing Fixtures : The plumbing fixtures are installed receptacles, devices, or appliances which are supplied with water or which receive or discharge liquids or liquid borne wastes, with or without discharge into the drainage system with which they may be directly or indirectly connected.

Plumbing System : The plumbing system includes the water supply and distribution pipes, plumbing fixtures and traps, soil, waste and vent pipes, building drains and building sewers, including their respective connections, devices, and appurtenances within the property lines of the premises, and water treating or water using equipment.

Public Sewer : A public sewer is a common sewer directly controlled by public authority. Also known as MAIN SEWER.

Relief Vent : A relief vent is a vent the primary function of which is to provide circulation of air between drainage and vent systems (Fig 8.7.6).

Riser : A water supply pipe that extends vertically one full storey or more to convey water to branches or fixtures.

Sanitary Sewer : A sanitary sewer is a pipe which carries sewage and excludes storm, surface, and ground water. Also known as SEWER.

SEEPAGE PIT : See SOAK PIT.

Septic Tank : A septic tank is a watertight receptacle which receives the discharge of a drainage system or part thereof and is designed and constructed so as to separate solids from the liquid, digest organic matter through a period of detention, and allow the liquids to discharge into the soil outside the tank through a system of open joint or perforated piping or disposal pit (Fig 8.7.15).

Service Latrine : A latrine from which the excreta are removed by manual agency and not by water carriage.

Sewage : The sewage is any liquid waste containing animal or vegetable matter in suspension or solution and may include liquids containing chemicals in solution.

Sewer : See BUILDING SEWER or PUBLIC SEWER or SANITARY SEWER or STORM SEWER.

SLUDGE : A settled portion of the sewage or waste water effluent from a sedimentation tank in semi-solid condition.

SOAK WELL : See SOAK PIT.

SOAK PIT : A pit, dug into permeable soil lined to form a covered perforated chamber or filled with sand at the bottom and gravel or broken bricks at the top into which effluent from a septic tank or storm water is led and from which these may soak away into the ground. Also known as SEEPAGE PIT or SOAK WELL.

Soil Pipe : A soil pipe is any pipe which conveys the discharge of water closets, urinals, or fixtures having similar functions, with or without the discharge from other fixtures, to the building drain or building sewer.

Soil Vent : See Stack Vent.

Stack : A stack is the vertical main of a system of soil, waste, or vent piping.

Stack Vent : A stack vent (sometimes called a waste vent or soil vent) is the extension of soil or waste stack above the highest horizontal drain connected to the stack. Also known as SOIL VENT.

Stack Venting : Stack venting is a method of venting a fixture or fixtures through the soil or waste stack.

Sterilizer Vent : A separate pipe or stack, indirectly connected to the building drainage system at the lower terminal, which receives the vapour from nonpressure sterilizers or the exhaust from pressure sterilizers and conduct the vapour directly to the outer air.

Storm Drain : See Building Storm Drain.

Storm Sewer : A storm sewer is a sewer used for conveying rain water, surface water, condensate, cooling water, or similar liquid wastes, exclusive of sewage and industrial waste. Also known as SEWER.

Subsoil Drain : A subsoil drain is a drain which receives only subsurface or seepage water and conveys it to a place of disposal.

SULLAGE : The discharge from wash basins, sinks and similar appliances, which does not contain human or animal excreta.

Sump : A sump is a tank or pit which receives sewage or liquid waste, located below the normal grade of the gravity system, and which must be emptied by mechanical means.

Supports : The supports, hangers, and anchors are devices for supporting and securing pipe and fixtures to walls, ceilings, floors, or structural members.

Trap : A trap is a fitting or device so designed and constructed as to provide, when properly vented, a liquid seal which will prevent the back passage of air without materially affecting the flow of sewage or waste water through it.

Trap Seal : The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap.

Vent Pipe : See Vent System.

Vent Stack : A vent stack is a vertical vent pipe installed primarily for the purpose of providing circulation of air to and from any part of the drainage system.

Vent System : A vent system is a pipe or pipes installed to provide a flow of air to or from a drainage system or to provide a circulation of air within such system to protect trap seals from siphonage and back pressure. Also known as VENT PIPE.

Vertical Pipe : A vertical pipe is any pipe or fitting which is installed in a vertical position or which makes an angle of not more than 45 degrees with the vertical.

Waste Pipe : A waste pipe is a pipe which conveys only liquid waste free of faecal matter.

7.4 DRAINAGE AND SANITATION PLANS

7.4.1 Requirement of Permit

Drainage and sanitation system shall not be installed until a permit for such work has been issued by the Authority for existing (only for addition or for alteration) or new building or for any other premises.

7.4.2 Application for Permit

An application for a permit for drainage and sanitation work shall be made on a prescribed form (see Appendix R) by the licensed plumber and the owner, or by his appointed person or agent to install all or a self-contained or workable part of such work. The application shall accompany building drainage plans and adequate description of the proposed drainage and sanitation installation in a drawing (drawn to a scale not less than 1:100) with the following details:

a) plan(s) of the building with typical arrangement of plumbing fixtures;

b) sanitary waste disposal system;

c) rainwater drainage system;

d) venting system in a building having more than 5 branch intervals;

e) relief vent system in a building having more than 10 branch intervals;

f) materials, sizes and gradients of all proposed piping;

g) the position of manhole, traps, waste pipe, rainwater pipe, vent pipe, water closet, urinal, lavatory, sink or other appliances in the premises and their connection with sewerage/drainage system or with private waste disposal system; the following colours may be used to indicate sewers, waste water pipes, rainwater pipes and existing works:

proposed sanitary sewers and sanitary waste disposal pipes - red

proposed storm sewers, waste water and rainwater pipes - blue

existing network - black

h) the position of refuse chute, inlet hopper and collection chamber for buildings more than five storeys high.

7.4.3 In addition to drainage plan a separate site plan of the building shall be submitted with the following particulars :

a) adjoining plots and streets with their identification;

b) the position and invert level of the public sewers (if any) and the direction of flow in it;

c) the level of the proposed drains connecting to the sewers (if any);

d) the position and layout of private waste disposal system (in absence of public sewers); and

e) the alignment, size and gradients of all drains.

7.4.4 For high rise and public buildings, design calculations and specifications for various items of the work involved shall be submitted along with the drawings.

7.4.5 Permits and Approvals

The building official shall examine or cause to be examined all applications for permits and, amendments thereto within 45 days. If the application does not conform to the requirements of all pertinent laws, such application shall be rejected in writing, stating the reasons therefor. If the proposed work satisfies all the Code requirements, the Authority shall issue a nontransferable permit.

7.5 LICENSING OF PLUMBER

7.5.1 Licence Requirement

No individual, partnership, corporation or firm shall engage in the business of installation, repair or alteration of drainage and sanitation work without obtaining a licence from the Authority.

7.5.2 Examination and Certification

The Authority shall establish a plumbers examination board. The board will determine the requirements for the qualification and procedures for examination of applicants for licence. The Authority will issue licence to such applicants who meet the qualifications therefor and successfully pass the examination conducted by the board.

7.5.3 Annulment of Licence

The licence of a licensed plumber may be nullified by the Authority, if it is proved that a plumbing work has been completed and certified by the licensed plumber violating the provisions of this Code deliberately setting aside the approvals given in the permit or without receiving the permit from the Authority.

7.6 DRAINAGE AND SANITATION REQUIREMENT

7.6.1 General

7.6.1.1 Each family dwelling unit on premises abutting a public sewer or with a private waste disposal system shall have at least one water closet and one kitchen sink or washing facilities. It is recommended to have at least one bathroom with a bath tub or shower to meet the basic requirements of sanitation and personal hygiene and in that case bath and water closet shall be separately accommodated.

7.6.1.2 All other structures for human occupancy or use on premises abutting a sewer or with a private waste disposal system shall have adequate sanitary facilities but in no case less than one water closet and one other fixture for cleaning purposes.

7.6.1.3 There shall be one water tap and arrangement for drainage in the vicinity of each water closet in all buildings.

7.6.1.4 There shall be at least one water tap and arrangement for drainage in the vicinity of each urinal or group of urinals in all buildings.

7.6.1.5 There shall be separate facilities for each sex for public toilets and for public bathing places based on the percentage of each anticipated sex.

7.6.1.6 Where drinking water fountain is provided, it shall not be installed in toilet room.

7.6.1.7 Rooms containing water closets or urinals shall be separated by partition wall from places where food will be prepared and served.

7.6.2 Minimum Number of Fixtures

Table 8.7.1 and Sec 7.6.2.1 and 7.6.2.2 provide the minimum number of fixtures required for different categories of buildings according to their occupancy classifications. The fixture requirement for the occupancy not provided in these sections shall be subject to the approval of the Authority.

7.6.2.1 Physically Handicapped Plumbing Facilities : All buildings other than residential, educational, storage and hazardous according to building occupancy classification, having public toilet facilities with required number of fixtures shall have at least one water closet for each sex (or one unisex water closet facility) and one drinking fountain accessible to and usable by physically handicapped persons. The water closet compartment for physically handicapped persons shall be in accordance with Sec 7.9.4.

7.6.2.2 Drainage and Sanitation Requirements for Traffic Terminal Stations

a) The minimum sanitary conveniences provided at any traffic terminal station like railway station, bus station etc. shall consist of nonservice type latrines one for each sex, and one nonservice type urinal for males for a daily passenger volume up to 300 persons. For large stations and airports, sanitary arrangements shall be in accordance with Table 8.7.1.

b) There shall be adequate arrangements for satisfactory drainage of all sewage, sullage and waste water. The drainage shall be so designed as to cause no stagnation at the maximum discharge rate for which the different units are designed.

c) Adequate scavenging arrangements shall be provided to keep the stations or terminals clear of all refuse. Refuse containers shall be placed at convenient points.

7.6.3 Accessibility

The fixtures specified in Sec 7.6.2 for public building shall be located not more than one floor above nor more than one floor below the floor occupied by the people for whose use the fixtures are intended, unless elevator service is available, except that in buildings which are accessible to the physically handicapped, there shall be minimum facilities as specified by the Code. It is desirable that the path of travel to the facilities shall not exceed a travel distance of 150 m.

7.7 MATERIALS AND APPLIANCES

Different sanitary appliances, materials and fittings listed in Tables 8.7.2 to 8.7.5 and 8.6.9 (Chapter 6) shall conform to the standard or one of the standards cited against them. For other appliances, materials and fittings not provided in Tables 8.7.2 to 8.7.5 and 8.6.9 (Chapter 6) shall be subject to the approval of the Authority. Applicable standards for different materials and appliances have also been listed in Part 5.

Table 8.7.2

Sanitary Appliances

Appliances	Standard
Ceramic wash basin and pedestals	BDS 1162-87
Ceramic wash down water closet pans	BS 1213
Foot rest vitreous china	BDS 1163-87 parts 1 & 4
Integrated squatting pans vitreous china	BDS 1163-87 parts 1 & 5
Metal hand rinse basin	BS 1329
Metal sink for domestic purpose	BS 1244
Urinals (bowl type) vitreous china	BDS 1163-87 parts 1 & 3
Washdown water closet pans, vitreous china	BDS 1163-87 parts 1 & 2
Water closet seat plastic	BS 1254
Water closet flushing cisterns and pipes	BS 1125

Table 8.7.3

Building Drainage and Vent Pipe

Material	Standards
Acrylonitrile butadiene styrene (ABS plastic pipe)	ASTM D2661, ASTM F 628
Aluminum tubing	ASTM B429, ASTM B745M
Brass pipe	ASTM B43
Cast iron pipe	ASTM A74
Copper or Copper-alloy tubing	ASTM B75M, ASTM B88M, ASTM B251M, ASTM B306
Galvanized steel pipe	ASTM A53
Lead pipe	IS 404
Polyvinyl chloride plastic pipe	ASTM D2665, ASTM D2949, ASTM F891

Table 8.7.4

Building Sewer or Building Storm Sewer Pipe

Material	Standards
Acrylonitrile butadiene styrene (ABS plastic pipe)	ASTM D2261, ASTM D2751, ASTM F628, ASTM D2321
Asbestos	BDS 428, BDS 429
Bihuminized fibre pipe	ASTM D1861, ASTM D1862
Cast iron pipe	ASTM A74
Concrete pipe	ASTM C14M, ASTM C76M
Copper or Copper-alloy tubing	ASTM B75, ASTM B88M, ASTM B251M
Polyvinyl chloride (PVC) plastic pipe	ASTM D2665, ASTM D2949, ASTM D3034, ASTM D2321, ASTM F891
Vitrified clay pipe	ASTM C4, ASTM C700

Table 8.7.5

Subsoil Drainage Pipe

Material	Standard
Asbestos cement pipe	ASTM C508
Bituminous fibre pipe	ASTM D2311
Cast iron pipe	ASTM A74
Concrete pipe	ASTM C654 M
Polyethyline (PE) plastic pipe	ASTM F405
Polyvinyl chloride (PVC) plastic pipe	ASTM D2729, ASTM F891
Vitrified clay pipe	ASTM C4, ASTM C700

7.8 hangers and support and pipe jointing

7.8.1 Hangers and Support

The piping, fixtures and equipment used for drainage system shall be provided with hangers and support in accordance with Sec 6.13 in Chapter 6.

7.8.2 Pipe Joints

The joints between different pipings and fittings shall conform to the standards cited against them in Table 8.7.6. The requirements for the joints not specified in the table shall be subject to the approval of the Authority.

7.9 DESIGN CONSIDERATIONS

7.9.1 Objective

For the design of drainage and sanitation system of different buildings according to building classification, the objective shall be to safeguard against fouling, deposit of solids and clogging and with adequate cleanouts and inspection chambers so arranged that the drains may be readily cleaned without the risk of health hazard.

7.9.2 General

a) The plumbing system shall be designed and adjusted to use the minimum quantity of water consistent with proper performance and cleaning.

b) Plumbing fixtures, devices and appurtenances shall be supplied with required volume of water at pressures adequate to enable these to function properly and without undue noise under normal conditions of use.

7.9.3 Different Plumbing Systems

For the design and installation for drainage piping, one of the following plumbing systems shall be used :

i) single stack system,

ii) one-pipe system, and

iii) two-pipe system.

Table 8.7.6

Joints Between Different Pipes and Fittings

Material	Standard
ABS plastic pipe and fittings	ASTM D2235, ASTM D2661, ASTM D3212, ASTM F628 ASME B1.20.1
Aluminium tubing	ASTM C564
Asbestos cement pipe and fittings	ASTM D1869
Brass pipe and fittings	ASME B1.20.1
Cast iron pipe and fittings	ASTM C564
Concrete pipe and fittings	ASTM C443
Copper or Copper-alloy pipe and fittings	ASTM B32, ASME B1.20.1
Copper-alloy tubing and fittings	ASTM B32
CPVC plastic pipe and fittings	ASTM F493, ASME B1.20.1
Galvanized steel pipe and fittings	ASME B1.20.1
PE plastic pipe and fittings	ASTM D2657
PVC plastic pipe and fittings	ASTM D2657, ASTM D2855, ASTM D3139, ASTM D3212, ASTM F402, ASTM F656, ASME B1.20.1
Vitrified clay pipe and fitting	ASTM C425

a) Single stack system may be used with 100 mm diameter stack for buildings up to 5-storey height. The fixtures in each floor shall be connected to a single stack for increasing the rate of discharge in the downward direction. There shall be at least 200 mm vertical distance between the waste branch and the soil branch connection, while the soil pipe will be connected to stack above the waste pipe. The size of soil branch shall not be less than 100 mm. The horizontal branch distance for fixtures from stack and bend(s) at the foot of stack to avoid back pressure as well as the vertical distance between the lowest connection and the invert of drain shall be as shown in Fig 8.7.1. The recommended depth of water seal trap for different fixtures shall be in accordance with Table 8.7.7.

b) Where all types of waste from the building are desired to be discharged into a common sewer or into same waste disposal system, one pipe system may be used (Fig 8.7.2).

c) Where the sullage from kitchen and bath will be dealt with separately, the two pipe system shall be used (Fig 8.7.3).

7.9.4 Water Closet Compartment for Physically Handicapped

7.9.4.1 Provision for Wheelchair Users : The water closet compartment for wheelchair users shall have at least the dimensions and fittings as shown in Fig 8.7.4.

7.9.4.2 Provision for Ambulant Disabled People : The minimum dimension for water closet compartment and the fittings for ambulant disabled people shall be as shown in Fig 8.7.5.

Fig 8.7.1

Table 8.7.7

Recommended Depth of Water Seal Trap for Different Fixtures

Fixture

Water Seal (mm)

Water Closets

Floor Traps

For Waste Branch of 75 mm diameter or More

For Waste Branch of Less Than 75 mm diameter

7.9.5 Installation of Drainage System

7.9.5.1 All plumbing fixtures shall be made of smooth and nonabsorbent materials, free from concealed fouling surfaces and may be located in ventilated enclosures.

7.9.5.2 Whenever possible, all drainage system shall be drained to the public sewer or private waste disposal system by gravity.

7.9.5.3 Horizontal drainage piping of 75 mm diameter and less shall be installed with a fall of not less than 20 mm per m.

Horizontal drainage piping larger than 75 mm diameter shall be installed with a fall of not less than 10 mm per m.

It is a good policy to design the system for the highest possible velocity. However, consideration should be given to the fact that the high velocities in pipes with slopes greater than 20 mm per m may cause self-siphonage of trap seal.

Fig 8.7.2

7.9.5.4 Where conditions do not permit building drains and sewers to be laid with a fall as great as that specified, a lesser slope may be permitted provided the computed velocity in the drains will not be less than 0.6 m per second. The maximum recommended velocity will be 2.5 m per second.

7.9.5.5 The soil pipe conveying any solid or liquid filth to a drain shall be circular with a minimum diameter of 100 mm.

7.9.5.6 The waste branch from bath room, wash basin or sink shall be of 32 mm to 50 mm diameter and shall be trapped immediately beneath such wash basins or sink by an efficient siphon trap with adequate means of inspection and cleaning. The minimum recommended size of waste stack is 75 mm.

7.9.5.7 The soil and waste stack shall be continued upward undiminished in size 0.6 m above the roof surface when the roof will be used only for weather protection. Where the roof will be used for any purpose other than weather protection, the soil and vent stack shall run at least 2 m above the roof surface so that there shall be the least possible nuisance.

7.9.5.8 The soil and waste stack shall be firmly attached to the wall with a minimum clearance of 50 mm from the wall.

Fig 8.7.3

7.9.5.9 All (soil, waste, vent or antisiphonage) stacks shall be covered on top with a copper or heavily galvanized iron wire dome or cast iron terminal guards.

7.9.6 Installation of Venting System

7.9.6.1 The vent stack or main vent shall be installed in conjunction with a soil or waste stack in a building containing five or more branch intervals. One vent stack may serve not more than two soil or waste stacks.

7.9.6.2 The building with building drain shall have at least one 100 mm vent stack or stack vent carried full size to outdoor air above the roof in accordance with Sec 7.9.5.7 above.

7.9.6.3 The diameter of a vent stack shall not be less than 50 mm.

7.9.6.4 The diameter of a branch vent pipe on a waste pipe shall not be less than 25 mm or two-thirds of the diameter of the branch waste pipe ventilated.

7.9.6.5 The branch vent pipe on a soil pipe shall not be less than 32 mm in diameter.

7.9.6.6 All main vents or vent stacks shall connect full size at their base to the building drain or to the soil or waste stack at or below the level of the lowest drainage connection to them. All vent stacks shall extend undiminished in size above the roof or shall be reconnected to a vent header or to the stack vent portion of the soil or waste stack, at least 150 mm above the flood level of the highest fixture connection discharging into the soil or waste stack. Where the roof is to be used for any purpose other than weather protection, the vent extension shall be in accordance with the Sec 7.9.5.7.

Fig 8.7.4

7.9.6.7 Offset in the stack vent portion of soil or waste stack, offset in vent stack and connection of vent stack at the bottom to soil or waste pipe or to the building drain shall be at an angle of at least 45 degrees to the horizontal.

7.9.6.8 All vent and branch vent pipe shall be so graded and connected that sufficient slope is provided for condensation to drain back to soil or waste pipe by gravity.

7.9.6.9 Where fixtures other than water closets discharge into the stack downstream of a water closet, each fixture connecting downstream shall be individually vented.

7.9.6.10 Soil and waste stacks in a building having more than 10 branch intervals shall be provided with a relief vent (Fig 8.7.6) at each tenth interval counting from the top floor.

7.9.7 Clearance of Blockages

7.9.7.1 There shall be sufficient and suitable access points at every change of alignment, gradient or diameter or at bends and junctions for clearing blockages from drains which cannot be reached by any other

Fig 8.7.5

means. Tables 8.7.8 and 8.7.9 show the maximum spacing and the recommended minimum dimensions for access fittings and chambers for the specified depth.

Table 8.7.8

Maximum Spacing of Access Points

		To
From	Access Fitting	Junction	Inspection Chamber	Manhole
	(m)	(m)	(m)	(m)
Start of external drain	12	-	22	45
Rodding eye	22	22	45	45
Access fitting †	-	12	22	22
Inspection chamber	22	22	45	45
Manhole	22	-	45	90
† higher spacing may be used for larger size access fitting.

7.9.7.2 Access should be one of the following four types :

i) rodding eyes - capped extensions of the pipes,

ii) access fittings - small chambers (or an extension of the pipes) but not with an open channel,

iii) inspection chambers - chambers with working space at ground level, and

iv) manholes - large chambers with working space at drain level.

Fig 8.7.6

7.9.7.3 Inspection chambers and manholes shall have removable nonventilating covers of durable material and be of suitable strength. Inspection chambers and manholes in buildings shall have mechanically fixed airtight covers unless the drain itself has watertight access covers. Manholes deeper than 1 m shall have metal step iron or fixed ladders. Fig 8.7.7 and 8.7.8 show the details of typical manholes at smaller depth (<1 m) and at higher depth (>1 m) respectively. Fig 8.7.9 shows the details of a drop manhole. The drop manhole is a manhole that serves as a junction and receives sewer lines at two different elevations.

Table 8.7.9

Minimum Dimensions for Access Points

Access Points	Depth (m)	Internal Sizes		Cover Sizes
		Length x width (mm x mm)	Diameter (mm)	Length x width (mm x mm)	Circular (mm)
Rodding eye		min. 100 mm or size of drains

Access fitting	0.6 or less	150 x 100	150	150 x 100	150
Inspection chamber	1.0 or less	450 x 450	450*	450 x 450	450*

Manhole	1.5 or less over 1.5 over 2.7	1200 x 750 1200 x 750 12000 x 840	1050 1200 1200	600 x 600 600 x 600 600 x 600	600 600 600
* 190 mm dia may be used for depth ≤ 0.6 m

Fig 8.7.7

Fig 8.7.8

7.9.8 Protection Against Rodent

Holes through walls shall be such that they will not provide passage of rodent or other insects from room to room or from floor to floor. Materials used for embedding pipes shall be rodent proof.

7.9.9 Bedding and Backfilling

The choice of bedding and backfilling depends on the depth of the bed, and size and strength of the materials. Fig 8.7.10 and Table 8.7.10 show the two types of bedding and backfilling and minimum and maximum depth of cover for each type of bedding for rigid pipings. The bedding and backfilling for flexible

Fig 8.7.9

pipings is shown in Fig 8.7.11. The minimum depth of bedding for flexible pipings shall be 0.9 m under any road and 0.6 m in fields and gardens.

The depth shall not be more than 10 m. The flexible pipe may be laid with less cover in fields and gardens. The bedding and backfilling shall be in accordance with Fig 8.7.12.

Table 8.7.10

Limits of Cover (m) for Standard Strength Rigid Pipes in any Width of Trench

Pipe Bore	Bedding	Fields and Gardens		Light Traffic Roads		Heavy Traffic Road
(mm)	Class	Min	Max	Min	Max	Min	Max
100	Type 1 Type 2	0.3 0.3	7.4 5.8	0.4 0.5	7.4 5.8	0.4 0.5	7.2 5.5
150	Type 1 Type 2	0.6 0.6	5.0 3.9	0.6 0.7	5.0 3.8	0.6 0.7	4.6 3.3

Fig 8.7.10

Fig 8.7.11, 8.7.12

7.9.10 Rainwater Drainage

7.9.10.1 Rainwater data for the locality of the building shall be studied to arrive at the design parameters for rainwater drainage in accordance with Appendix S.

7.9.10.2 In case of inclined roof, the horizontal projection shall be considered as the roof drainage area.

7.9.10.3 Rainwater from roof or from building premises shall not be discharged into septic tank. This will be drained into storm sewer or combined sewer system where available or into private disposal methods (water course or dry well, Fig 8.7.13 and 8.7.14), or storage tank, where rainwater will be used for domestic purpose.

Fig 8.7.13, 8.7.14

7.9.10.4 Large dry well shall be constructed in accordance with the requirements for seepage pit (Sec 7.9.12). However, for small dry wells handling limited quantities of rainwater, the pit may consist of an one metre length of 0.45 m diameter pipe filled with crushed stone.

7.9.10.5 Where rainwater will be used for domestic purpose, rainwater from roof or terrace may be led straight from conductor (or leader) to one or more storage tanks. Storage tanks shall be provided with ventilating covers. An arrangement shall be made in the rainwater leader to divert the first washings from the roof or terrace catchment as they will contain more undesirable materials. The open end of all pipes shall be covered with mosquito (insect) proof wire net.

7.9.10.6 Individual rain water traps shall be installed on the rainwater drain branch serving each leader or a single trap shall be installed in the main rainwater drain (building storm drain) just before its connection with the combined building sewer, main drain or public sewer.

7.9.10.7 No traps shall be required for rainwater drains which will be connected to a sewer draining rainwater exclusively.

7.9.10.8 Subsurface drainage pipings for rainwater drainage shall not be less than 100 mm in diameter. The subsoil drainage system shall be protected by an accessibly located backwater valve in case the building is subject to backwater or flooding. Subsoil drains shall discharge to a trapped area drain, sump, dry well or an approved location above grade.

7.9.10.9 Rainwater pipes shall not be used as soil, waste or vent pipes.

7.9.10.10 All roof areas, except those draining to hanging gutters, shall be equipped with roof drains with strainers extending not less than 100 mm above the surface of the roof and shall have an available inlet area not less than two times the area of the leader to which the drain will be connected.

7.9.10.11 It is recommended to have more than one rainwater drainage pipe for primary roof drainage system to minimize blockage.

7.9.10.12 It is recommended to provide secondary rainwater drainage system at a suitable elevation from the roof that has been considered in the calculation of rainwater load to design the building structure. The secondary drainage system shall be a separate drainage piping up to storm sewer or private waste (rainwater) disposal system. The size of secondary rainwater drainage piping shall not be less than the size required for primary rainwater drainage piping.

7.9.10.13 French drains may be employed as surface water drains for drainage of unpaved surfaces.

7.9.11 Septic Tank

7.9.11.1 Septic tank(s) (Fig 8.7.15 and 8.7.16) discharging into either a subsurface disposal field or one or more seepage pits shall be required for the approval of drainage and sanitation plans for the places where public sewers are not available.

Fig 8.7.15

Fig 8.7.16

7.9.11.2 Such disposal method shall be designed by a licensed professional in accordance with the requirement of the provisions of this Code.

7.9.11.3 The design of such system shall be on the basis of location with respect to wells or other sources of water, soil permeability, ground water elevation, area available and maximum occupancy of the building.

7.9.11.4 Rainwater or ground water shall not be discharged into the septic tank.

7.9.11.5 Septic tank(s) shall not discharge into open water courses.

7.9.11.6 The minimum distance for various components of the disposal system shall be in accordance with Table 8.7.11.

7.9.11.7 The flow into a septic tank may be calculated on the basis of water consumption rate or on the basis of plumbing fixtures discharging simultaneously into it.

7.9.11.8 The septic tank shall have a minimum liquid capacity of 2000 litres, minimum width 1 m and minimum liquid depth 1 m. The length of a septic tank shall be at least twice its width. It is recommended that the length of a septic tank be not more than 4 times its width.

7.9.11.9 The maximum size of a septic tank shall be limited to the number of users not exceeding 300 persons for residential buildings (occupancy groups A, C, and D) and 1000 persons for all other occupancy groups . It is recommended to use independent parallel chamber septic tank for a population more then 100 persons for residential buildings (for occupancy groups A, C and D) and 350 persons for all other occupancy groups.

7.9.11.10 The diameter of a circular septic tank shall not be less than 1.4 m and shall have a operating liquid depth not less than 1 m.

7.9.11.11 The volume required for digested sludge and scum may be computed on the basis of 0.04 m3/capita/year.

7.9.11.12 The liquid retention time of a septic tank shall be at least 1 day.

7.9.11.13 The desludging frequency of a septic tank shall be at least once a year.

7.9.11.14 It is recommended to use two chamber septic tank when the capacity of a septic tank exceeds 3000 litres. The inlet compartment of a two chamber septic tank shall have a capacity not less than two-third of its total capacity (Fig 8.7.16).

Table 8.7.11

Location of Components of Sewage Disposal System

System Component	Distance (m)
	Building Foundation	Well	Stream	Seepage Pit	Dry Well
Septic tank	1.5	8	-	1.5	-
Disposal field	3	15	7.5	6	6
Seepage pit	4.5	15	15	6	6
Dry well	3	15	-	6	-

7.9.11.15 The septic tank shall be constructed of corrosion resistant material and be of permanent water tight construction. The manhole cover and the roof of the tank shall be designed for at least 7 kPa live load. The inlet compartment shall be provided with a manhole. Outlet compartment may also be provided with a manhole. The design guideline of a septic tank is presented in Appendix T.

7.9.12 Disposal Field and Seepage Pit

7.9.12.1 A distribution box shall be provided to receive the effluent from the septic tank to assure equal distribution to each individual line of disposal field. The distribution box shall be connected to the septic tank by a watertight sewer line and shall be located at the upper end of disposal field. Fig 8.7.17 shows the plans and sections of typical distribution boxes.

Fig 8.7.17

7.9.12.2 Soil percolation tests (at least for three holes) shall be performed at the site of a proposed individual sewage disposal system installation to determine the suitability of soil and site.

7.9.12.3 The liquid capacity (volume below inlet line) of seepage units (disposal field or seepage pit) shall be at least twice that of a septic tank. Effective absorption area of seepage unit may be computed in accordance with Table 8.7.12.

7.9.12.4 No seepage unit shall be extended into water table directly

7.9.12.5 Each disposal field shall have at least two outlet distribution lines from the distribution box. No portion of disposal field shall be installed under any pavement or any area where there will be vehicular traffic or parking

7.9.12.6 Minimum standards for disposal field construction shall be as shown in Table 8.7.13.

Table 8.7.12

Absorptive Capacity of Disposal Field and Seepage Pit

Percolation Test Rate in

Minutes for Water to Fall

25 mm

Effluent Allowance Rate of Seepage Unit

in litre per m2 per day

Disposal Field Trenches

(bottom of trench)

Seepage Pit

(wall area)

2 or less

60 (not recommended)

over 60 (not suitable)

128

172

128

Table 8.7.13

Design Features of Disposal Field

Number of lateral branches2

Maximum length of branch20 m

Minimum diameter of field distribution pipe100 mm

Maximum slope of field distribution pipe3.3 mm per m

Depth of trench0.45 m to 9 m

Trench bottom, minimum above ground water0.61 m

Trench bottom width0.45m to 0.75m

Depth of coarse material

under pipe 150 mm

over pipe 50 mm

Size of coarse material12 mm to 63 mm

7.9.12.7 Seepage pit (soak pit) shall be lined with stone, brick or concrete blocks laid up dry with open joints that are backed up with at least 75 mm coarse aggregate. The joints above the inlet shall be sealed with cement mortar. A reinforced concrete cover shall be provided. For cover area more than 0.75 m2 the pit shall have an access manhole. The bottom of the pit shall be filled with coarse gravel, or crushed stone/brick to a depth of 0.3 m. Figure 8.7.18 provides the details of a seepage pit.

7.10DESIGN OF DRAINAGE AND SANITATION SYSTEM

7.10.1 Estimation of Maximum Load Weight of Waste Water

The design of drainage piping depends on the load weight of all connected fixtures that might operate at any one time. The total load weight in soil or waste pipes is related to the probability of usage of connected fixtures to those pipes. To estimate the total load weight carried by a soil or waste pipe, the relative load weight for different kinds of fixtures are provided in Table 8.7.14. Table 8.7.15 provides an approximate rating of those fixtures not listed in Table 8.7.14. Therefore, the maximum load weight on any piping in terms of fixture units may be estimated knowing the number and type of connected fixtures to a pipe using Tables 8.7.14 and 8.7.15.

7.10.2 Gradient and Size of Pipe

7.10.2.1 The building drains and sewer shall be designed to discharge the peak simultaneous load weight flowing half-full with a minimum self-cleansing velocity of 0.75 m per second. However, flatter gradient may be used if required but the minimum velocity shall not be less than 0.6 m per second. Again, it is undesirable to employ gradients giving a velocity of flow greater than 2.5 m per second.

Fig 8.7.18

7.10.2.2 The maximum number of fixture units that may be connected to a given size of building sewer, building drain, horizontal branch or vertical soil or waste stack shall be as provided in Tables 8.7.16 and 8.7.17.

7.10.3 Size of Rainwater Piping

7.10.3.1 The size of vertical leaders shall be based on the maximum projected roof area according to Table 8.7.18.

7.9.3.2 The size of building storm drain, storm sewer or any of their horizontal branches shall be based on the maximum projected roof or paved area to be drained in accordance with Table 8.7.19.

7.10.3.3 The size of semi-circular gutter shall be based on maximum projected roof area according to Table 8.7.20.

7.10.4 Size of Vent Piping

7.10.4.1 The size of vent piping shall be determined from its length and the total of the fixture units connected thereto in accordance with Table 8.7.21.

7.10.4.2 The branch vent shall be sized in accordance with Table 8.7.22.

7.11 CONSTRUCTION RELATING TO CONVEYANCE OF RAINWATER AND SANITARY WASTES

7.11.1 Conveyance of Rainwater

7.11.1.1 All junctions and joints of rainwater piping shall be watertight.

7.11.1.2 Roof gutters shall be of suitable material of required thickness. All joints shall be watertight.

7.11.1.3 Construction of french drains (if used) shall be in accordance with established engineering practices.

7.11.2 Conveyance of Sanitary Wastes

7.11.2.1 The layout of drainage systems shall be simple. Change of direction and gradient shall be minimized and shall be as easy as practicable.

7.11.2.2 The excavation, where necessary, shall be made in accordance with Table 8.7.23.

Table 8.7.14

Fixture Units for Different Sanitary Appliances or Groups

Type of Fixture

Fixture

Unit Value

as Load Factors

One bathroom group consisting of water closet, wash basin and bath tub or shower stall :

a) Flush Tank water closet

b) Flush-valve water closet

Bathtub*

Bidet

Combination sink and tray (drain board)

Drinking fountain

Floor traps†

Kitchen sink, domestic

Wash basin, ordinary‡

Wash basin, surgeon's

Shower stall, domestic

Shower (group) per head

Urinal, wall lip

Urinal, stall

Water closet, tank operated

Water closet, valve operated

0.5

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

† Size of floor trap shall be determined by the area of surface water to be drained.

‡ Wash basin with 32 mm and 40 mm trap have the same load value.

Table 8.7.15

Fixture Unit Values for Fixtures Based on Fixture Drain or Trap Size

Fixture Drain on Trap Size

Fixture Unit

Value

30 mm and smaller

40 mm

50 mm

65 mm

75 mm

100 mm

Table 8.7.16

Maximum Number of Fixture Units that can be Connected to Branches and Stacks

Diameter

of Pipe

Maximum Number of Fixture Units that can be Connected

(mm)

Any Horizontal Fixture

Brancha

One Stack of

3 Storeys in

Height or 3

Intervals

More than 3 Storeys in Height

Total for Stack

Total at One

Storey or Branch

Interval

100

125

150

200

250

300

375

160

360

620

1400

2500

3900

7000

240

540

960

2200

3800

6000

500

1100

1900

3600

5600

8400

200

350

600

1000

1500

a Does not include branches of the building sewer.

bSizing load based on design criteria

Table 8.7.17

Maximum Number of Fixture Units that can be Connected to

Building Drains and Sewers

Diameter

of Pipe

Maximum Number of Fixture Units that can be Connected to any

Portion* of the Building Drain or the Building Sewer for Various Slopes

(mm)

1/200

1/100

1/50

1/25

100

150

200

250

300

375

1400

2500

2900

7000

180

700

1600

2900

4600

8300

216

840

1920

3500

5600

10000

250

1000

2300

4200

6700

12000

* Includes branches of building sewer

Table 8. 7.18

Size of Vertical Leaders*

Size of Leader **	Maximum Projected Roof Area and Flow
(mm)	(m2)	(/min)
50 65 75 100 125 150 200	202 367 598 1287 2336 3790 8180	87 155 253 544 986 1602 3450
* Table 8.7.18 is based upon a maximum rainfall of 25 mm per hour for a 1-hour duration. The figure for drainage area shall be adjusted to local conditions (Appendix T). ** The equivalent diameter of square leader will be the diameter of that circle which can be inscribed within the cross-sectional area. The equivalent diameter of the rectangular leader will be the short dimension of the rectangular leader. However, the ratio of width to depth of rectangular leader shall not exceed 3:1.

Table 8.7.19

Size of Horizontal Building Storm Drains and Building Storm Sewer *

Diameter of Drain (mm)	Maximum Projected Area and Flow for Various Slopes
	10 mm per m		20 mm per m		40 mm per m
	m2	/min	m2	/min	m2	/min
75 100 125 150 200 250 300 375	299 668 1215 1950 4185 7550 12140 21700	125 288 515 823 1765 3185 5100 9120	422 965 1715 2745 5940 10650 17140 30600	177 406 725 1157 2500 4500 7236 12900	599 1370 2430 3900 8380 15100 24280 43400	252 577 1030 1645 3540 6370 10250 18300
* Table 8.7.19 is based upon a maximum rainfall of 25 mm per hour for 1-hour duration. The figure for drainage area shall be adjusted to local conditions in accordance with Appendix T.

Table 8.7.20

Size of Semicircular Roof Gutters*

Dia of Gutter (mm)	Maximum Projected Roof Area for Gutter of Various Slopes
	5 mm per m		10 mm per m		20 mm per m		40 mm per m
	m	/min	m2	/min	m2	/min	m2	/min
75 100 125 150 175 200 250	61 130 227 350 503 725 1300	25 55 96 148 210 307 555	87 185 320 495 710 1020 1850	36 77 136 210 300 430 785	123 260 455 700 1000 1300 2610	51 110 192 296 425 610 1110	174 370 645 1010 1420 2040 3650	73 155 273 425 600 862 1540
* Table 8.7.20 is based upon a maximum rainfall of 25 mm per hour for 1-hour duration. The figure for drainage area shall be subject to local conditions in accordance with Appendix T.

7.11.2.3 The depth of cover shall be in accordance with Sec 7.9.8.

7.11.2.4 The pipe shall be laid to even gradients and change of gradient shall be combined with an access point (Sec 7.9.6). However, access points shall be provided only if blockages could not be cleared without them.

7.11.2.5 The joints and connection in drainage and venting system shall be gastight and watertight for the pressures required by the test, with the exception of those portions of perforated or open joint piping which will be installed for the purpose of collecting and conveying ground or seepage water to the underground storm drains.

7.11.2.6 Piping in a drainage and venting system shall be installed without undue strains and stresses and provision shall be made for expansion, contraction and structural settlement. Vertical piping shall be secured at sufficiently close intervals to keep the pipe in alignment and carry the weight of the piping and its content. The horizontal piping shall be supported at sufficiently close intervals (Sec 7.8) to keep it in alignment and to prevent sagging.

7.12 REFUSE CHUTE SYSTEM

7.12.1 All buildings higher than 6-storeys shall be provided with refuse chute system for transporting and collecting refuse from different floors in a sanitary way. The refuse shall be received from the respective floor through an inlet hopper in to the chute which conveys refuse and discharges into the collection chamber. The refuse from the collection chamber shall be cleared at suitable intervals.

7.12.2 The refuse chute, inlet hopper and collection chamber shall be constructed with smooth and nonflammable materials.

7.12.3 The hopper shall be self-cleaning and shall be fitted with self-closing shutter to prevent the passage of foul gases inside the building.

7.12.4 The diameter of the chute shall not be less than 300 mm. It shall be adequately ventilated at the top. The chute shall be provided with suitable arrangements for flushing with water for the full length.

Table 8.7. 21

Size and Length of Vent Stacks and Stack Vents

Diameter

of Soil

or Waste

Stack

(mm)

Total Fixture Unit (FU)

Connected to fixture

Maximum Development Length of Vent (m)*

for Diameter (mm) of Vent Pipes

100

125

150

200

250

300

100

125

150

200

250

300

375

102

140

320

540

190

490

940

1400

500

1100

2000

2900

1800

3400

5600

7600

4000

7200

11000

15000

7300

13000

20000

26000

15000

25000

38000

50000

45.5

30.5

22.5

12.5

9.5

7.5

45.5

30.5

45.5

33.5

28.5

10.5

6.5

91.5

109.5

19.5

16.5

8.5

6.5

5.5

4.5

317

247

207

189

45.5

6.5

298.5

228.5

195

176.5

97.5

39.5

30.5

25.5

23.5

9.5

5.5

301.5

231.5

204

180

122

94.5

9.5

5.5

305

237.5

201

183

48.5

42.5

23.5

15.5

9.5

5.5

286.5

219.5

186

170.5

94.5

36.5

28.5

9.5

292.5

225.5

192

173.5

116

91.5

39.5

24.5

22.5

286.5

219.5

186

152.5

94.5

* The development length shall be measured from the vent connection to the open air

7.12.5 The collection chamber shall be of suitable size and located at ground level.

7.12.6 The design and arrangement of the system shall be in accordance with established engineering practices.

7.13 Health care drainage system

7.13.1 General

The health care drainage system shall comply with applicable drainage and venting requirements specified in this chapter and with this section.

7.13.2 Special Fixtures and Equipment

The hospital shall be provided with clinical sink, bedpan washer and such other fixtures and equipment for disposal of bedpan contents and for the cleansing and disinfection of such fixtures. A clinical sink shall not be considered as a substitute for service sink.

Table 8.7.22

Minimum Diameter and Maximum Length of Individual, Branch,

and Circuit Vents for Horizontal Drainage Branches

Diameter of

Horizontal

Drainage

Branch (mm)

Slope of Horizontal

Drainage

Branch (mm/m)

Maximum Development

Length of Vent (m) for Diameter (mm) of Vent Pipe

100

125

150

200

250

100

125

150

200

250

300

NL*

115

137

29.5

128

14.5

48.5

29.5

125

149

39.5

29.5

39.5

27.5

11.5

94.5

45.5

9.5

125

152

33.5

54.5

128

* NL means no limit; Actual value in excess of 150 m.

Table 8.7.23

Minimum Width at Bottom of Trench

Depth of Trench (m)	Width of Trench (m)
Up to 1.2	Diameter of pipe plus 0.4
Above 1.2	Diameter of pipe plus 0.45
Note: Trench top width shall not be less than 0.75 m for depths exceeding 0.9 m

7.13.3 Bedpan Washer and Clinical Sink

Bedpan washer and clinical sink shall be connected to soil stacks through a water seal trap. The bedpan washer with vapour vent connection shall be provided with additional local vent stack. The minimum vent stack size for bedpan washer shall be in accordance with Table 8.7.24.

Table 8.7.24

Minimum Vent Stack Size

No of Bedpan Washer

Diameter (mm)

Up to 3 bedpan washers at different floors

4 to 6 bedpan washers

7 to 12 bedpan washers

100

The bottom of the bedpan local vent stack (except for one bedpan washer) shall be drained indirectly into sanitary drainage system through traps. The size of the trap and connecting pipe shall be at least the size of the vent stack. At least 6 mm diameter water supply piping shall be taken from each flush supply of each bedpan washer on the discharge side of vacuum breaker, trapped to form 75 mm or more trap seal and connected to the local vent stack on each floor.

7.13.4 Sterilizer Vent Stack

The pressure or nonpressure sterilizer shall have vent connection to the sterilizer vent stack. This vent connection shall be accessible for inspection and cleaning. The size of sterilizer vent stack shall be as follows:

7.13.4.1 Pressure Sterilizers : The minimum diameter for pressure sterilizer vent stack shall be 63 mm. The stack size for combinations of pressure sterilizer exhaust shall be in accordance with Table 8.7.25.

7.13.4.2 Pressure Instrument Washer Sterilizers : The minimum size of sterilizer vent stack for instrument washer sterilizer shall be 50 mm for up to two sterilizers. The 75 mm stack will serve up to four sterilizers.

7.13.4.3 Nonpressure Sterilizers : The minimum diameter of nonpressure sterilizer vent stack shall be 50 mm for utensil sterilizer and 38 mm for instrument sterilizer. Multiple installation shall be sized in accordance with Table 8.7.26.

7.13.4.4 Bedpan Steamers : The diameter for one bedpan steamer shall be 38 mm. The stack size for combinations shall be in accordance with Table 8.7.26.

Table 8.7.25

Pressure Sterilizer Vent Stack Size

Stack Size ( mm)	Number of Connections Permitted for Different Combination Sizes (mm)
	19	25	31	38
38	3	-	-	-
38	-	2	-	-
38	-	-	1	-
38	2	1	-	-
50	6	-	-	-
50	-	3	-	-
50	-	-	2	-
50	-	-	-	1
50	3	2	-	-
50	2	1	1	-
50	1	1	-	1
75	15	-	-	-
75	-	7	-	-
75	-	-	5	-
75	-	-	-	3
75	1	5	-	1
75	-	1	2	2

7.13.5 Vent Extension

The termination of vent stack shall be in accordance with Sec 7.9.5.7 and 7.9.6.6.

7.13.6 Special Fixture Drainage

The device, appurtenance and appliance required for special purposes such as refrigerators, ice boxes, cooling or refrigerating coils etc. shall be protected against backflow with adequate air gap between the equipment outlet and drainage inlet.

Table 8.7.26

Nonpressure Sterilizer Vent Stack or Bedpan Steamer Sizes

Stack Sizes (mm)	No of Connections Permitted for Different Connection Sizes(mm)
	38	50
38	1	-
50	2	-
50	-	1
50	1	1
75	4	-
75	-	2
75	2	2
100	8	-
100	-	4
100	4	4

7.13.7 Mental Health Care Centre

The pipes and traps used in mental health care buildings shall not be exposed and all fixtures shall be securely bolted through walls.

7.14 INSPECTION, TESTING AND COMPLETION CERTIFICATE

7.14.1 Inspection

The new drainage and sanitation system or part of existing system shall not be covered or enclosed or put into operation until it has been inspected, tested and approved by the Authority. The Authority may examine the appliances and fittings before their installation or during the progress of the work. An installation of plumbing work, whether new or existing, which is found to be defective or unsafe shall not be allowed to continue in use unless corrections have been made to comply with the Code requirements.

7.14.2 Testing

7.14.2.1 Drainage and Venting System : The piping of drainage and venting system shall be tested first with water. The final test of completed drainage and venting system may be done by smoke test. The water and smoke tests shall be performed as described below:

a) Water Test : The water test shall be applied to the drainage and venting system either for the whole system or part (section) thereof . For the entire system, all openings in the piping except the highest opening shall be closed, and the system filled with water to the point of overflow. For the system to be tested in sections, each opening shall be tightly plugged except the highest opening of the section under test and each section shall be filled with water but no section shall be tested with less than a 3 m head of water. In testing successive sections, at least the upper 3 m of the next preceding section shall be tested so that no joint or pipe in the building (except the top most 3 m of the system) shall have been submitted to a test of less than a 3 m head of water. The water shall be kept in the system or in the portion under test for at least 15 minutes before the inspection starts. The system or the part of the system under test shall be watertight at all points.

b) Smoke Test : The final test for gas and watertightness of the completed drainage and venting system may be performed by smoke test. The test is performed by filling all traps with water and then introducing smoke into the system produced by one or more smoke machines. When the smoke appears at the stack openings on the roof, they shall be closed and a pressure equivalent to 25 mm head of water shall be built and maintained for 15 minutes before inspection starts.

7.14.2.2 Building Sewer : The Connection between building sewer and public sewer or individual sewage disposal system shall be closed by inserting a test plug. The building sewer shall be filled with water under a pressure of not less than 30 kPa for at least 15 minutes. The system shall be able to maintain the test pressure.

7.14.3 Completion Certificate

After the installation of drainage and sanitation system, the licensed plumber shall give a completion certificate to the authority in a prescribed form (Appendix U) for inspection and testing. After testing, the Authority will give the final approval (as presented in completion certificate form, in the Appendix U) to use the system .

7.15 GUIDE TO MAINTENANCE

7.15.1 The drainage and sanitation system shall be maintained in a sanitary and safe operating condition by the owner or his designated agent. All device or safeguards required by the Code shall be maintained in working order.

7.15.2 The following operations shall be carried out during periodical cleaning of a drainage and sanitation system:

a) The covers of inspection chambers and manholes shall be removed and the side benching and channels shall be scrubbed.

b) All lengths of main and branch drains shall be rodded by means of drain rods and a suitable rubber or leather plunger. After rodding, the drains shall be thoroughly flushed with clean water.

c) The ladders/rings in deep manholes and the manhole covers shall be painted.

d) All surface water drains shall be cleaned.

e) All subsoil drains shall be examined for obstruction at the open joints.

f) Refuse chute system shall be cleaned.

g) The rain water drainage system with primary drainage piping alone shall be properly maintained to avoid stagnation of water due to blockages.

Related Appendices

Appendix R Application for Permit to Construct Drainage and Sanitation System

Appendix S One-hour Rainfall

Appendix T Design Guideline of a Septic Tank

Appendix U Completion Certificate (Drainage and Sanitation Works)

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Source: Bangladesh National Building Code 2006 (Housing and Building Research Institute). Superseded by BNBC 2020 — provided for reference. For design or official work, refer to the printed code.

Chapter 7 — Drainage and Sanitation

7.1 PURPOSE

7.2 SCOPE

7.3 TERMINOLOGY

7.4 DRAINAGE AND SANITATION PLANS

7.4.1 Requirement of Permit

7.4.2 Application for Permit

7.4.5 Permits and Approvals

7.5 LICENSING OF PLUMBER

7.5.1 Licence Requirement

7.5.2 Examination and Certification

7.5.3 Annulment of Licence

7.6 DRAINAGE AND SANITATION REQUIREMENT

7.6.1 General

7.6.2 Minimum Number of Fixtures

7.6.2.2 Drainage and Sanitation Requirements for Traffic Terminal Stations

7.6.3 Accessibility

7.7 MATERIALS AND APPLIANCES

7.8 hangers and support and pipe jointing

7.8.1 Hangers and Support

7.8.2 Pipe Joints

7.9 DESIGN CONSIDERATIONS

7.9.1 Objective

7.9.2 General

7.9.3 Different Plumbing Systems

7.9.4 Water Closet Compartment for Physically Handicapped

7.9.5 Installation of Drainage System

7.9.6 Installation of Venting System

7.9.7 Clearance of Blockages

7.9.7.2 Access should be one of the following four types :

0.6 or less

1.0 or less

1.5 or less

7.9.8 Protection Against Rodent

7.9.9 Bedding and Backfilling

7.9.10 Rainwater Drainage

7.9.11 Septic Tank

7.9.12 Disposal Field and Seepage Pit

7.9.12.4 No seepage unit shall be extended into water table directly

7.10DESIGN OF DRAINAGE AND SANITATION SYSTEM

7.10.1 Estimation of Maximum Load Weight of Waste Water

7.10.2 Gradient and Size of Pipe

7.10.3 Size of Rainwater Piping

7.10.4 Size of Vent Piping

7.11 CONSTRUCTION RELATING TO CONVEYANCE OF RAINWATER AND SANITARY WASTES

7.11.1 Conveyance of Rainwater

7.11.2 Conveyance of Sanitary Wastes

7.12 REFUSE CHUTE SYSTEM

7.13 Health care drainage system

7.13.1 General

7.13.2 Special Fixtures and Equipment

7.13.3 Bedpan Washer and Clinical Sink

7.13.4 Sterilizer Vent Stack

7.13.5 Vent Extension

7.13.6 Special Fixture Drainage

7.13.7 Mental Health Care Centre

7.14 INSPECTION, TESTING AND COMPLETION CERTIFICATE

7.14.1 Inspection

7.14.2 Testing

7.14.3 Completion Certificate

7.15 GUIDE TO MAINTENANCE

7.15.2 The following operations shall be carried out during periodical cleaning of a drainage and sanitation system: