Section H1 Foul Water Drainage

Requirement

Foul water drainage

H1. (1) An adequate system of drainage shall be provided to carry foul water from appliances within the building to one of the following, listed in order of priority:

(a) a public sewer; or, where that is not reasonably practicable,
(b) a private sewer communicating with a public sewer; or, where that is not reasonably practicable,
(c) either a septic tank which has an appropriate form of secondary treatment or another wastewater treatment system; or, where that is not reasonably practicable,
(d) a cesspool.

(2) In this Part ‘foul water’ means waste water which comprises or includes:

(a) waste from a sanitary convenience, bidet or appliance used for washing receptacles for foul waste; or
(b) water which has been used for food preparation, cooking or washing.

Limits on application

Requirement H1 does not apply to the diversion of water which has been used for personal washing or for the washing of clothes, linen or other articles to collection systems for re-use.

Guidance

Performance
In the Secretary of State’s view the requirement of H1 will be met if a foul water drainage system:

a. conveys the flow of foul water to a foul water outfall (a foul or combined sewer, a cesspool, septic tank or holding tank);

b. minimises the risk of blockage or leakage;

c. prevents foul air from the drainage system from entering the building under working conditions;

d. is ventilated;

e. is accessible for clearing blockages; and

f. does not increase the vulnerability of the building to flooding.

Introduction to provisions

1.1 The capacity of the system should be large enough to carry the expected flow at any point.

1.2 The capacity depends on the size and gradient of the pipes. Minimum sizes and gradient limits are given in the text.

1.3 The pipe sizes quoted in this document are nominal sizes used as a numerical designation in convenient round numbers approximately equal to a manufacturer’s size. Equivalent pipe sizes for individual pipe standards will be found in the standards listed in Tables 4, 7 and 14.

 

  1. Section 1: Sanitary pipework
    1. Section 2: Foul drainage
      1. Appendix H1-A: Additional guidance for larger buildings
        1. Appendix H1-B: Repairs, alterations and discontinued use of drains and sewers
          1. Appendix H1-C: Adoption of sewers and connection to public sewers

    Section 1: Sanitary pipework

    1.1 The provisions in this section are applicable to domestic buildings and small non-domestic buildings. Further guidance on larger buildings is given in Appendix A. Complex systems in larger buildings should be designed in accordance with BS EN 12056 (see paragraph 1.39).

    1.2 The guidance in these provisions is applicable for WCs with major flush volumes of 5 litres or more. Where WCs with major flush volumes less than 5 litres are used, consideration should be given to the increased risk of blockages. Guidance on the design of sanitary pipework suitable for use with WCs with major flush volumes as low as 4 litres can be found in BS EN 12056 (see paragraph 1.39).

    Traps

    1.3 All points of discharge into the system should be fitted with a trap (e.g. a water seal trap) to prevent foul air from the system entering the building. Under working and test conditions traps should retain a minimum seal of 25mm of water or equivalent.

    1.4 Table 1 gives minimum trap sizes and seal depths for the appliances which are most used (for other appliances see Appendix paragraph A4).

    1.5 Pressure fluctuation – To prevent the water seal from being broken by the pressures which can develop in the system the branch discharge pipes should be designed as described in paragraphs 1.7 to 1.25.

    1.6 Access for clearing blockages – If a trap forms part of an appliance the appliance should be removable. All other traps should be fitted directly after the appliance and should be removable or be fitted with a cleaning eye.

    Table 1 Minimum trap sizes and seal depths Part H1

    Table 1 Minimum trap sizes and seal depths Part H1

    Branch discharge pipes

    1.7 Branch pipes should discharge into another branch pipe or a discharge stack unless the appliances discharge to a gully. Gullies are generally at ground floor level, but may be at basement level. Branch pipes should not discharge into open hoppers.

    1.8 If the appliances are on the ground floor the pipe(s) may discharge to a stub stack or discharge stack, directly to a drain or (if the pipe carries only wastewater) to a gully. (See paragraphs 1.11 and 1.30.)

    1.9 A branch pipe from a ground floor closet should only discharge directly to a drain if the depth from the floor to the drain is 1.3m or less (see Diagram 1).

    Diagram 1 Direct connection of ground Floor WC to a drain Part H1
    Diagram 1 Direct connection of ground Floor WC to a drain Part H1

    Diagram 2 Branch connection to stacks- crossflow prevention Part H Diagram 2 Branch connection to stacks- crossflow prevention Part H

    1.10 A branch pipe should not discharge into a stack in a way which could cause crossflow into any other branch pipe. (See Diagram 2.)

    1.11 A branch discharge pipe should not discharge into a stack lower than 450mm above the invert of the tail of the bend at the foot of the stack in single dwellings of up to 3 storeys (see Diagram 2). (For multi-storey buildings this should be increased, see Appendix paragraphs A5 and A6.)

    1.12 Branch pipes may discharge into a stub stack. (See paragraph 1.30.)

    1.13 A branch pipe discharging to a gully should terminate between the grating or sealing plate and the top of the water seal.

    1.14 Condensate drainage from boilers may be connected to sanitary pipework. The connection should be made using pipework of minimum diameter 22mm through a 75mm condensate trap. If an additional trap is provided externally to the boiler to provide the 75mm seal, an air gap should be provided between the boiler and the trap.

    a. The connection should preferably be made to an internal stack with a 75mm condensate trap.

    b. If the connection is made to a branch pipe, the connection should be made downstream of any sink waste connection.

    c. All sanitary pipework receiving condensate should be made from materials resistant to a pH value of 6.5 and lower. The installation should be in accordance with BS 6798.

    1.15 Sizes of branch pipes – Pipes serving a single appliance should have at least the same diameter as the appliance trap (see Table 1). If a pipe serves more than one appliance, and is unventilated, the diameter should be at least the size shown in Table 2.

    1.16 Bends in branch pipes should be avoided if possible. Where they cannot they should have as large a radius as possible.

    1.17 Junctions on branch pipes of about the same diameter should be made with a sweep of 25mm radius or at 45°. Connection of branch pipes of 75mm diameter or more to a stack of equal diameter should be made with a sweep of 50mm minimum radius or at 45°.

    1.18 Branch pipes up to 40mm diameter joining branch pipes 100mm diameter or greater should, if practicable, connect to the upper part of the pipe wall of the larger branch.

    1.19 Ventilation of branch pipes – separate ventilation will not be needed to prevent the water seals in traps from being lost by pressures which can develop in the system if the length and slope of the branch discharge pipes do not exceed those shown in Table 2 or Diagram 3.

    Table 2 Common branch discharge pipes unventilated Part H
    Table 2 Common branch discharge pipes unventilated Part H1

    Diagram 3 Branch Connections Part H Diagram 3 Branch Connections Part H1

    1.20 If the figures in Table 2 and Diagram 3 are exceeded the branch pipe should be ventilated by a branch ventilating pipe to external air, to a ventilating stack (ventilated branch system) or internally by use of an air admittance valve.

    1.21 A separate ventilating stack is only likely to be preferred where the numbers of sanitary appliances and their distance to a discharge stack are large. (See Appendix paragraphs A7 to A9.)

    1.22 Branch ventilating pipes – should be connected to the discharge pipe within 750mm of the trap and should connect to the ventilating stack or the stack vent, above the highest ‘spillover’ level of the appliances served (see Diagram 4). The ventilating pipe should have a continuous incline from the discharge pipe to the point of connection to the ventilating stack or stack vent.

    Diagram 4 Branch ventilation pipes part H1
    Diagram 4 Branch ventilation pipes part H1

    1.23 Branch ventilating pipes which run direct to outside air should finish at least 900mm above any opening into the building nearer than 3m (see Diagram 6 and paragraph 1.31).

    1.24 Branch ventilating pipes to branch pipes serving one appliance should be at least 25mm diameter or where the branch is longer than 15m or has more than 5 bends, should be at least 32mm.

    1.25 Rodding points should be provided to give access to any lengths of discharge pipe which cannot be reached by removing traps or appliances with internal traps (see paragraph 1.6).

    Discharge stacks

    1.26 All stacks should discharge to a drain. The bend at the foot of the stack should have as large a radius as possible and at least 200mm at the centre line.

    1.27 Offsets in the ‘wet’ portion of a discharge stack should be avoided. If they are unavoidable then in a building of not more than 3 storeys there should be no branch connection within 750mm of the offset. In a building over 3 storeys a ventilation stack may be needed with connections above and below the offset. In buildings over 3 storeys discharge stacks should be located inside the building.

    1.28 Sizes of stacks – Stacks should have at least the diameter shown in Table 3 and should not reduce in the direction of flow. Stacks serving urinals should be not less than 50mm, stacks serving closets with outlets less than 80mm should be not less than 75mm and stacks serving closets with outlets greater than 80mm should be not less than 100mm. The internal diameter of the stack should be not less than that of the largest trap or branch discharge pipe. For larger buildings the maximum flow should be checked. (See paragraphs A.1 to A.3.)

    Table 3 Minimum Diameters for discharge stacks Part H Table 3 Minimum Diameters for discharge stacks Part H1

    1.29 Ventilation of discharge stacks – To prevent water seals in the traps from being lost by pressures which can develop in the system, discharge stacks should be ventilated. Discharge stacks connected to drains liable to surcharging or near an intercepting trap require ventilating pipes of not less than 50mm diameter connected to the base of the stack above the likely flood level.

    1.30 Stub stacks – A stub stack may be used if it connects into a ventilated discharge stack or into a ventilated drain not subject to surcharging and no connected water closet has a floor level more than 1.3m and no other branch into the stub stack has a centreline more than 2m to the centre line above the invert of the connection or drain (see Diagram 5).

    Diagram 5 Stub stack Part H1 Diagram 5 Stub stack Part H1

    1.31 Ventilating pipes open to outside air should finish at least 900mm above any opening into the building within 3m and should be finished with a wire cage or other perforated cover, fixed to the end of the ventilating pipe, which does not restrict the flow of air (see Diagram 6). In areas where rodent control is a problem (see paragraph 2.22) these should be metallic.
    Diagram 6 Termination of ventilation stacks or ventilation part of discharge Part H1

    Diagram 6 Termination of ventilation stacks or ventilation part of discharge Part H1

    1.32 Sizes of stack ventilation pipes – stack ventilation pipes (the dry part above the highest branch) may be reduced in size in one and two storey houses, but should be not less than 75mm.

    1.33 Ventilated discharge stacks may be terminated inside a building when fitted with air admittance valves complying with BS EN 12380:2002. Where these valves are used they should not adversely affect the amount of ventilation necessary for the below ground system which is normally provided by open stacks of the sanitary pipework. Air admittance valves should be located in areas which have adequate ventilation, should be accessible for maintenance and should be removable to give access for clearance of blockages. Air admittance valves should not be used outside buildings or in dust laden atmospheres. Where there is no open ventilation on a drainage system or through connected drains, alternative arrangements to relieve positive pressures should be considered.

    1.34 Access for clearing blockages – rodding points should be provided in discharge stacks to give access to any lengths of pipe which cannot be reached from any other part of the system. All pipes should be reasonably accessible for repair. Rodding points in stacks should be above the spillover level of appliances.

    Materials for pipes, fittings and joints

    1.35 Any of the materials shown in Table 4 may be used (the references are to British Standard or European Standard Specifications). Where necessary different metals should be separated by non-metallic material to prevent electrolytic corrosion. Care should be taken to ensure continuity of any electrical earth bonding requirements. Pipes should be firmly supported without restricting thermal movement. Attention is also drawn to the requirement of Part B of Schedule 1 to the Building Regulations 2000 and guidance in the Approved Document relating to penetration of fire separating elements and fire stopping provisions.

    Table 4 Materials for sanitary pipework Part H
    Table 4 Materials for sanitary pipework Part H1

    1.36 Sanitary pipework connected to WCs should not allow light to be visible through the pipe wall, as this is believed to encourage damage by rodents.

    Workmanship

    1.37 Good workmanship is essential. Workmanship should be in accordance with BS 8000 Workmanship on Building Sites Part 13: Code of practice for above ground drainage.

    Air tightness

    1.38 The pipes, fittings and joints should be capable of withstanding an air test of positive pressure of at least 38mm water gauge for at least 3 minutes. Every trap should maintain a water seal of at least 25mm. Smoke testing may be used to identify defects where a water test has failed. Smoke testing is not recommended for PVC-U pipes.

    Alternative approach
    1.39 The requirement can also be met by following the relevant recommendations of BS EN 12056 Gravity drainage systems inside
    buildings. Relevant clauses are in Part 1: General and performance requirements, Clauses 3–6; Part 2 Sanitary pipework, layout and calculation, Clauses 3 to 6 and National Annexes NA to NG (System III is traditionally in use in the UK); Part 5 Installation and testing, instructions for operation, maintenance and use, Clauses 4–6, 8, 9 and 11. BS EN 12109 Vacuum Drainage Systems Inside Buildings.

     

    Section 2: Foul drainage

    Table 5 Flow rates from dwellings Part H

    Table 5 Flow rates from dwellings Part H1

    2.1 This section gives guidance on the construction of underground drains and sewers from buildings to the point of connection to an existing sewer or a cesspool or wastewater treatment system and includes any drains or sewers outside the curtilage of the building. Disused and defective pipework is known to harbour rats (see Appendix H1-B).

    2.2 Some public sewers may carry foul water and rainwater in the same pipes. If the drainage system is also to carry rainwater to such a sewer, the following provisions still apply but the pipe sizes may need to be increased to carry the combined flows (see paragraph 2.35). In some circumstances, separate drainage should still be provided (see Approved Document H5).

    Outlets

    2.3 Foul drainage should be connected to a public foul or combined sewer wherever this is reasonably practicable. For small developments connection should be made to a public sewer where this is within 30m provided that the developer has the right to construct the drainage over any intervening private land. Where levels do not permit drainage by gravity a pumping installation should be provided (see paragraphs 2.36 to 2.39).

    2.4 For larger developments it may be economic to connect to a public sewer even where the sewer is some distance away. For developments comprising more than one curtilage, the developer may requisition a sewer from the sewerage undertaker who has powers to construct sewers over private land (see Appendix H1-C, C.4).

    2.5 The sewerage undertaker should be notified at least three weeks before it is intended to connect to the public sewer (see Appendix H1-C, C.7).

    2.6 Where it is not reasonably practicable to connect to a public sewer, it may be possible to connect to an existing private sewer that connects with a public sewer. The permission of the owner or owners of the sewer will be required. The sewer should be in satisfactory condition and have sufficient capacity to take the additional flows.

    2.7 Where none of these options is reasonably practicable, a wastewater treatment system or cesspool should be provided (see Approved Document H2).

    Surcharging of drains

    2.8 Combined and rainwater sewers are designed to surcharge (i.e. the water level in the manhole rises above the top of the pipe) in heavy rainfall. Some foul sewers also receive rainwater and therefore surcharge. For low-lying sites (where the ground level of the site or the level of a basement is below the ground level at the point where the drainage connects to the public sewer) care should be taken to ensure that the property is not at increased risk of flooding. In all such cases the sewerage undertaker should be consulted to determine the extent and possible frequency of the likely surcharge.

    2.9 For basements containing sanitary appliances, where the risk of flooding due to surcharge of the sewer is considered by the sewerage undertaker to be high, the drainage from the basement should be pumped (see paragraphs
    2.36 to 2.39). Where the risk is considered to be low an anti-flooding valve should be installed on the drainage from the basement.

    2.10 For other low-lying sites (i.e. not basements) where risk is considered low, sufficient protection for the building may be possible by provision of a gully outside the building at least 75mm below the floor level. This should be positioned so that any flooding from the gully will not damage any buildings. In higher risk areas an anti-flooding valve should be provided, or the drainage system pumped (see paragraph 2.36 to 2.39).

    2.11 Anti-flooding valves should preferably be of the double valve type, and should be suitable for foul water and have a manual closure device. They should comply with the requirements of prEN 13564. A single valve should not normally serve more than one building. A notice should be provided inside the building to indicate that the system is drained through such a valve. This notice should also indicate the location of any manual override, and include advice on necessary maintenance.

    2.12 All drainage unaffected by surcharge should by-pass the protective measures and discharge by gravity.

    Layout

    2.13 The layout of the drainage system should be kept simple. Changes of direction and gradient should be minimised and as easy as practicable. Access points should be provided only if blockages could not be cleared without them.

    2.14 Connection of drains to other drains or private or public sewers, and of private sewers to public sewers, should be made obliquely, or in the direction of flow.

    2.15 Connections should be made using prefabricated components. Where holes are cut in pipes a drilling device should be used to avoid damaging the pipe.

    2.16 Where connections made to existing drains or sewers involve removal of pipes and insertion of a junction, repair couplings should be used to ensure a watertight joint and the junction should be carefully packed to avoid differential settlement with adjacent pipes.

    2.17 Sewers (serving more than one property) should be kept as far as is practicable away from the point on a building where a future extension is likely (e.g. rear of a house, or side of house where there is room for a side extension).

    2.18 The system should be ventilated by a flow of air. A ventilating pipe should be provided at or near the head of each main drain. An open ventilating pipe (without an air admittance valve) should be provided on any drain fitted with an intercepting trap (particularly on a sealed system), and on any drain subject to surcharge. Ventilated discharge stacks may be used (see paragraphs 1.27 and 1.29). Ventilating pipes should not finish near openings in buildings (see paragraph 1.31).

    2.19 Pipes should be laid to even gradients and any change of gradient should be combined with an access point (see paragraph 2.49).

    2.20 Pipes should also be laid in straight lines where practicable but may be laid to slight curves if these can still be cleared of blockages. Any bends should be limited to positions in or close to inspection chambers or manholes (see paragraph 2.49) and to the foot of discharge and ventilating stacks. Bends should have as large a radius as practicable.

    2.21 Drainage serving kitchens in commercial hot food premises should be fitted with a grease separator complying with BS EN 1825-1:2004 and designed in accordance with BS EN 1825-2:2002 or other effective means of grease removal.

    Special protection – rodent control

    2.22 Where the site has been previously developed the local authority should be consulted to determine whether any special measures are necessary for control of rodents. Special measures which may be taken include the following.

    a. Sealed drainage – drainage having access covers to the pipework in the inspection chamber instead of an open channel. These should only be used in inspection chambers, where maintenance can be carried out from the surface without personnel entry.

    b. Intercepting traps – These are susceptible to blockage and require frequent maintenance. Intercepting trap stoppers should be of the locking type that can be easily removed from the chamber surface and securely replaced after blockage clearance. It is important that stoppers are replaced after maintenance. These should only be used in inspection chambers where maintenance can be carried out from the surface without personnel entry.

    c. Rodent barriers – a number of rodent barrier devices are used in other countries; these include: enlarged sections on discharge stacks to prevent rats climbing, flexible downward facing fins in the discharge stack, or one way valves in underground drainage.

    d. Metal cages on ventilator stack terminals should also be used to discourage rats from leaving the drainage system (see paragraph 1.31).

    e. Covers and gratings to gullies may be displaced or attacked by rats. Solid plastic covers or metal gratings which can be fixed in place should be used to discourage rats from leaving the system.

    Protection from settlement

    2.23 A drain may run under a building if at least 100mm of granular or other flexible filling is provided round the pipe. On sites where excessive subsidence is possible additional flexible joints may be advisable or other solutions such as suspended drainage, particularly where the pipe is adjacent to structures or where soil conditions change in the course of the pipe run. Where the crown of the pipe is within 300mm of the underside of the slab, special protection should be provided (see paragraph 2.44).

    2.24 At any points where pipes are built into a structure, including an inspection chamber, manhole, footing, ground beam or wall, suitable measures should be taken to prevent damage or misalignment. This may be achieved by either:

    a. building in a length of pipe (as short as possible) with its joints as close as possible to the wall faces (within at most 150mm) and connected on each side of rocker pipes by a length of at most 600mm and flexible joints (see Diagram 7(a));

    or

    b. forming an opening to give at least 50mm clearance all round the pipe and the opening masked with rigid sheet material to prevent ingress of fill or vermin. It is important that the void is also filled with a compressible sealant to prevent ingress of gas (see Diagram 7(b)).

    2.25 A drain trench should not be excavated lower than the foundations of any building nearby (see Diagram 8) unless either:

    a. where the trench is within 1m of the foundation the trench is filled with concrete up to the lowest level of the foundation; or

    b. where the trench is further than 1m from the building, the trench is filled with concrete to a level below the lowest level for the building equal to the distance from the building, less 150mm.

    Diagram 7 Pipes Penetrating walls Part H2

    Diagram 7 Pipes Penetrating walls Part H2

    Diagram 8 Pipe runs near buildings Part H2

    Diagram 8 Pipe runs near buildings Part H2

    2.26 Where pipes are to be laid on piles or beams or in a common trench, or where the ground may prove unstable particularly where there is a high water table, advice may be found in TRL A guide to the design loadings for buried rigid pipes. The local authority may be able to provide information regarding the site.

    Depth of pipe cover

    2.27 The depth of cover will usually depend on the levels of the connections to the system, the gradients at which the pipes should be laid and the ground levels.

    2.28 Pipes also need to be protected from damage and if the limits of cover are not attainable it may be possible to choose another pipe strength and pipe bedding class combination (Guidance is given in BS EN 1295-1 National Annex NA). Alternatively special protection can be provided (see paragraphs 2.41 to 2.45).

    Pipe gradients and sizes

    2.29 Drains should have enough capacity to carry the flow. The flow depends on the appliances connected (see paragraphs 0.1–0.3 and Table 5) and the capacity depends on the size and gradient of the pipes (see Diagram 9).

    Diagram 9 Discharge capacities of foul drains running 0.75 proportional depth Part H
    Diagram 9 Discharge capacities of foul drains running 0.75 proportional depth Part H

    Table 5 Flow rates from dwellings Part H
    Table 5 Flow rates from dwellings Part H1

    2.30 Sewers (i.e. a drain serving more than one property) should normally have a minimum diameter of 100mm when serving no more than 10 dwellings. Sewers serving more than 10 dwellings should normally have a minimum diameter of 150mm. See also Table C1.

    2.31 The flow depends on the type, number and grouping of appliances.

    2.32 Appliances are seldom in use simultaneously and the minimum drain sizes in normal use are capable of carrying the flow from quite large numbers of appliances. Table 5 shows approximate flow rates resulting from the typical household group of 1 WC, 1 bath, 1 or 2 washbasins, 1 sink and 1 washing machine used for design purposes in BS EN 12056.

    2.33 A drain carrying foul water should have an internal diameter of at least 75mm. A drain carrying effluent from a WC or trade effluent should have an internal diameter of at least 100mm.

    2.34 Table 6 shows the flattest gradients at which drains should be laid (depending on the flow and the appliances connected to them) and the capacity they will then have (see also paragraphs 0.1–0.3).

    Table 6 Recommended minimum gradients for foul drains Part H
    Table 6 Recommended minimum gradients for foul drains Part H1>

    2.35 Combined systems – the capacity of systems carrying foul water and rainwater should take account of the combined peak flow (see Approved Document H3 Rainwater drainage paragraph 3.8).

    Pumping installations

    2.36 Where gravity drainage is impracticable, or protection against flooding due to surcharge in downstream sewers is required, a pumping installation will be needed.

    2.37 Package pumping installations are available which are suitable for installation within buildings. Floor mounted units may be particularly suited for installation in basements. These should conform to BS EN 12050. Pumping installations for use inside buildings should be designed in accordance with BS EN 12056-4.

    2.38 Package pumping installations suitable for installation outside buildings are also available. Guidance on the design of pumping installations for use outside buildings may be found in
    BS EN 752-6.

    2.39 Where foul water drainage from a building is to be pumped, the effluent receiving chamber should be sized to contain 24-hour inflow to allow for disruption in service. The minimum daily discharge of foul drainage should be taken as 150 litres per head per day for domestic use. For other types of building, the capacity of the receiving chamber should be based on the calculated daily demand of the water intake for the building. Where only a proportion of the foul sewage is to be pumped, then the capacity should be based pro-rata. In all pumped systems the controls should be so arranged to optimise pump operation.

    Materials for pipes and jointing

    Table 7 Materials for below ground gravity drainage Part H1
    Table 7 Materials for below ground gravity drainage Part H1

    2.40 Any of the materials shown in Table 7 may be used (the references are to British Standard Specifications). Joints should be appropriate to the material of the pipes. To minimise the effects of any differential settlement pipes should have flexible joints. All joints should remain watertight under working and test conditions and nothing in the pipes, joints or fittings should project into the pipe line or cause an obstruction. Different metals should be separated by non-metallic materials to prevent electrolytic corrosion.

    Bedding and backfilling

    2.41 The choice of bedding and backfilling depends on the depth at which the pipes are to be laid and the size and strength of the pipes.

    2.42 Rigid pipes – The types of bedding and backfilling which should be used for rigid pipes of standard strength laid in a trench of any width are shown in Diagram 10 and Tables 8 and 9. Minimum and maximum depths of cover are also shown for each type.

    2.43 Flexible pipes – These will become deformed under load and require support to limit the deformation. The bedding and backfilling should be as shown in Diagram 10. Minimum and maximum depths of cover are also shown in Table 10.

    Diagram 10 Bedding for pipes Part H
    Diagram 10 Bedding for pipes Part H2

    2.44 Where pipes have less than the minimum recommended cover in Table 8, 9 or 10, the pipes should, where necessary, be protected from damage by a reinforced concrete cover slab with a flexible filler and at least 75mm of granular material between the top of the pipe and the underside of the flexible filler below the slabs (see Diagram 11 and paragraphs 2.28, 2.42 and 2.43).

     2.45 Where it is necessary to backfill the trench with concrete in order to protect nearby foundations (see paragraph 2.25) movement joints formed with compressible board should be provided at each socket or sleeve joint face (see Diagram 12).

    Table 8 Limits of cover for class 120 clayware pipes in any width of trench Part H
    Table 8 Limits of cover for class 120 clayware pipes in any width of trench Part H1

    Table 9 Limits of cover for class M concrete pipes in any width of trench Part H

    Table 9 Limits of cover for class M concrete pipes in any width of trench Part H1

    Table 10 Limits of cover for thermoplastic (nominal ring stiffness SN4) pipes in any width of trench Part H
    Table 10 Limits of cover for thermoplastic (nominal ring stiffness SN4) pipes in any width of trench Part H1

    Diagram 11 Protection for pipes laid in shallow depths (minimum sizes) Part H
    Diagram 11 Protection for pipes laid in shallow depths (minimum sizes) Part H2

    Clearance of blockages

    2.46 Sufficient and suitable access points should be provided for clearing blockages from drain runs which cannot be reached by any other means. The siting, spacing and type of the access points will depend on the layout, depth and size of the runs.

    2.47 The provisions described below are for normal methods of rodding (which need not be in the direction of flow) and not mechanical means of clearing.

    2.48 Access points should be one of four types. Tables 11 and 12 show the depth at which each type should be used and the recommended dimensions it should have. The dimensions should be increased at junctions if they do not allow enough space for branches. The types are:

    Diagram 12 Joints for concrete encased pipes(minimum sizes) Part H
    Diagram 12 Joints for concrete encased pipes(minimum sizes) Part H2

    a. rodding eyes – capped extensions of the pipes;

    b. access fittings – small chambers on (or an extension of) the pipes but not with an open channel;

    c. inspection chambers – chambers with working space at ground level;

    d. manholes – deep chambers with working space at drain level.

    2.49 Siting of access points – access should be provided at the following points:

    a. on or near the head of each drain run, and

    b. at a bend and at a change of gradient, and

    c. at a change of pipe size (but see below if it is at a junction), and

    d. at a junction unless each run can be cleared from an access point (some junctions can only be rodded through from one direction).

    Table 11 Minimum dimensions for access fittings and inspection chambers Part H
    Table 11 Minimum dimensions for access fittings and inspection chambers Part H1

    Table 12 Minimum dimensions for manholes Part H
    Table 12 Minimum dimensions for manholes Part H1

    2.50 Access should be provided to long runs. The distances between access points depend on the types of access used but should not be more than shown in Table 13 for drains up to and including 300mm.

    2.51 Access points to sewers (serving more than one property) should be in places where they are accessible and apparent for use in an emergency. Examples of suitable locations include highways, public open space, unfenced front gardens and shared or unfenced driveways.

    2.52 Construction of access points – these should contain the foul water under working and test conditions and resist the entry of groundwater and rainwater. Any of the materials shown in Table 14 may be used.

    2.53 Where half round channels are used in inspection chambers and manholes the branches up to and including 150mm diameter should discharge into the channel in the direction of flow at or above the level of the horizontal diameter.
    A branch with a diameter >150mm should be set with the soffit level with that of the main drain. Where the angle of the branch is more than 45° a three quarter section branch should be used. Channels and branches should be benched up at least to the top of the outgoing pipe and at a slope of 1 in 12. The benching should be rounded at the channel with a radius of at least 25mm.

    Table 13 Maximum spacing for access points in metres Part H1
    Table 13 Maximum spacing for access points in metres Part H1

    Table 14 Materials for access points Part H1
    Table 14 Materials for access points Part H1

    2.54 Inspection chambers and manholes should have removable non-ventilating covers of durable material (such as cast iron, cast or pressed steel, precast concrete or plastics) and be of suitable strength. Small lightweight access covers should be secured (for example with screws) to deter unauthorised access (for example by children). Inspection chambers and manholes in buildings should have mechanically fixed airtight covers unless the drain itself has watertight access covers. Manholes deeper than 1m should have metal step irons or fixed ladders.

    Workmanship

    2.55 Good workmanship is essential. Workmanship should be in accordance with BS 8000 Workmanship on Building Sites Part 14: Code of practice for below ground drainage.

    2.56 During construction, drains and sewers which are left open should be covered when work is not in progress to prevent entry by rats.

    2.57 Any drain or sewer should be protected from damage by construction traffic and heavy machinery. Protection may be provided by providing barriers to keep such traffic away from the line of the sewer. Heavy materials should not be stored over drains or sewers.

    2.58 Where piling works are being carried out care should be taken to avoid damage to any drain or sewer. The position of the drain or sewer should be established by survey. If the drain or sewer is within 1m of the piling, trial holes should be excavated to establish the exact position of the sewer. The location of any connections should also be established. Piling should not be carried out where the distance from the outside of the sewer to the outside of the pile is less than two times the diameter of the pile.

    Testing and inspection

    2.59 Water tightness – after laying, including any necessary concrete or other haunching or surrounding and backfilling, gravity drains and private sewers should be tested for water tightness using either an air test or a water test. Information on test requirements is given in paragraphs 2.60 and 2.61 for pipe sizes up to 300mm. For further information and for larger sizes see BS 8000 Part 14 or BS EN 1610.

    2.60 Air test – for pipes up to 300mm diameter, the pipe should be pressurised up to a pressure of 110mm water gauge and held for approximately 5 minutes prior to testing. Following this the pipe should be able to hold an initial 100mm pressure with a maximum loss of head on a manometer of 25mm in a period of 7 minutes.

    2.61 Water test – For pipes up to 300mm diameter the system should be filled with water up to a depth of 5m above the lowest invert in the test section and a minimum depth of 1m measured at the highest invert in the test section. This may then be left for a period (one hour is generally sufficient) to condition the pipe. The test pressure should then be maintained for a period of 30 minutes, by topping up the water level as necessary so that it is within 100mm of the required level throughout the test. The losses per square metre of surface area should not exceed 0.15 litres for test lengths with only pipelines or 0.20 litres for test lengths including pipelines and manholes, or 0.40 litres for tests with only manholes and inspection chambers alone (i.e. no pipelines).

    2.62 Connectivity – Where separate drainage systems are provided (see Approved Document H5), connections should be proven to ensure that they are connected to the correct system.

    Alternative approach

    2.63 The requirement can also be met by following the relevant recommendations of BS EN 752. The relevant clauses are in Part 3, Part 4 and Part 6. BS EN 752, together with BS EN 1610 and BS EN 1295, contains additional information about design and construction. BS EN 12056 describes the discharge unit method of calculating flows. Also by providing systems meeting the requirements of BS EN 1091 Vacuum sewerage systems outside buildings, or BS EN 1671 Pressure sewerage systems outside buildings.

     

    Appendix H1-A: Additional guidance for larger buildings

    Capacity of pipes
    (see paragraph 1.28)

    A.1 The flow depends on the type, number and grouping of appliances.

    A.2 Appliances are seldom in use simultaneously and the minimum stack sizes in normal use are capable of carrying the flow from quite large numbers of appliances. Table A1 shows approximate flow rates resulting from the typical household group of 1 WC, 1 bath, 1 or 2 washbasins, 1 sink and 1 washing machine used for design purposes in BS EN 12056.

    Table A1 Flow rates from dwellings Part H
    Table A1 Flow rates from dwellings Appendix H1

    A.3 Flow rates for other commonly used appliances not covered in Table A1 are shown in Table A2.

    Table A2 Flow rates from appliances Part H
    Table A2 Flow rates from appliances Appendix H1

    Traps
    (see paragraph 1.4)

    A.4 Minimum trap sizes and seal depths for appliances not listed in Table A2 are shown in Table A3.

    Table A3 Minimum trap sizes and seal depths additional to Table 2 Part H
    Table A3 Minimum trap sizes and seal depths additional to Table 2 Appendix H1

    Branch discharge pipes

    (see paragraph 1.10)

    A.5 A branch pipe should not discharge  into a stack less than 750mm above the invert of the tail of the bend at the foot of the stack in a multi- storey building up to 5 storeys. Alternatively a branch pipe serving any ground floor appliance may discharge direct to a drain or into its own stack.

    A.6 If the building has more than 5 storeys ground floor appliances, unless discharging to a gully or drain, should discharge into their own stack. If the building has more than 20 storeys ground floor appliances, unless discharging to
    a gully or drain, and first floor appliances should discharge into their own stack.

    Ventilating stacks
    (see paragraph 1.21)

    A.7 A dry stack may provide ventilation for branch ventilation pipes as an alternative to carrying them to outside air or to a ventilated discharge stack (ventilated system).

    A.8 Ventilation stacks serving buildings with not more than 10 storeys and containing only dwellings should be at least 32mm diameter (for all other buildings see paragraph 1.29).

    A.9 The lower end of a stack may be connected directly to a ventilated discharge stack below the lowest branch discharge pipe connection and above the bend at the foot of the stack or to the crown of the lowest branch discharge pipe connection providing it is ø75mm diameter.

    Greywater recovery systems

    A.10 Sanitary pipework and underground drainage used to collect greywater for recovery and re-use within the building should be designed and constructed in accordance with the guidance in this Approved Document.

    A.11 All pipework carrying greywater for re-use should be clearly marked with the word ‘GREYWATER’ in accordance with Water Regulations Advisory Scheme Information Guidance Note 09-02-05 Marking and Identification of Pipework for Reclaimed and Grey Water Systems.

    A.12 Guidance on external storage tanks is given in Approved Document H2.

    A.13 Further guidance on greywater recovery systems can be found in the Water Regulations Advisory Scheme leaflet No. 09-02-04 Reclaimed Water Systems. Information about installing, modifying or maintaining reclaimed water systems.

     

    Appendix H1-B: Repairs, alterations and discontinued use of drains and sewers

    Legislation

    B.1 Although the Building Regulations do not include requirements for the continuing maintenance or repair of drains and sewers,local authorities and sewerage undertakers have powers to ensure that adequate maintenance
    is carried out, that repairs and alterations are carried out properly, and that disused drains and sewers are sealed.

    Power to examine and test

    B.2 Under Section 48 (Power of local authority to examine and test drains etc. believed to be defective) of the Public Health Act 1936 the local authority may test any drain or sewer where it appears to them that they have reasonable grounds for believing that is in such a condition:

    a. as to be prejudicial to health or a nuisance (for example it is harbouring rats);

    or

    b. (for those drains or sewers indirectly connecting to a public sewer) is so defective that groundwater leaks into it.

    B.3 Under Section 114 (Power to investigate defective drain or sewer) of the Water Industry Act 1991, sewerage undertakers may examine and test any drain or private sewer connecting with a public sewer, where it appears to them that they have reasonable grounds for believing that is in such a condition:

    a. as to be injurious or likely to cause injury to health or be a nuisance; or

    b. is so defective that subsoil water leaks into it.

    Power to require repairs

    B.4 Under Section 59 (Drainage of building) of the Building Act 1984 the local authority may require the owner of a building to carry out remedial works where a soil pipe, drain or private sewer is:

    a. insufficient;

    b. in such a condition as to be prejudicial to health or a nuisance; or

    c. so defective that subsoil water leaks into it.

    Power to repair drains or private sewers

    B.5 Under Section 17 (Power to repair drains etc. and to remedy stopped up drains etc.) of the Public Health Act 1961, as amended, local authorities have powers to repair or remove blockages on drains or private sewers which are not sufficiently maintained or kept in good repair or are stopped up, provided the cost does not exceed £250. They must first give notice to the owner. The costs may be recovered from the owner or owners of the drain or sewer.

    Repair, reconstruction or alterations to underground drains or sewers

    B.6 Although repairs, reconstruction or minor alterations to drains or sewers are not normally covered under the Building Regulations, local authorities have other powers to control such works.

    B.7 Material alterations to existing drains and sewers are, however, covered under the Building Regulations.

    B.8 Notice to be given before repairs or alterations are carried out. Under Section 61 (Repair etc. of drain) of the Building Act 1984, any person intending to repair, reconstruct or alter a drain must, except in an emergency, give 24 hours notice to the local authority of their intention to carry out the works. Where the works are carried out in an emergency they shall not cover over the work without giving such notice. They must also give free access to the local authority to inspect the works.

    B.9 The local authority may, if appropriate, use their powers under Section 48 of the 1936 Public Health Act (see paragraph B.2) to test the drain, or under Section 59 of the Building Act 1984 (see paragraph B.4) to require remedial works.

    Sealing or removal of disused drains or sewers

    B.10 Disused drains and sewers offer ideal harbourage to rats and frequently offer a route for them to move between sewers and the surface. They could also collapse causing subsidence.

    B.11 Under Section 62 (Disconnection of drain) of the Building Act 1984, any person who carries out works which result in any part of a drain becoming permanently disused, they shall seal the drain at such points as the local authority may direct.

    B.12 Section 82 (Notices about demolition) of the Building Act 1984 allows the local authority to require any person demolishing a building to remove or seal any sewer or drain to which the building was connected.

    B.13 Under Section 59 (Drainage of building) of the Building Act 1984, the local authority can require the owner of a building to remove, or
    otherwise render innocuous, any disused drain or sewer which is prejudicial to health or a nuisance.

    Guidance

    B.14 Paragraphs B.15 to B.19 give guidance on the appropriate methods associated with the repair and alteration of drains and sewers, and the removal or sealing of disused drains and sewers.

    Repairs and alterations

    B.15 Repairs, reconstruction and alterations to existing drains and sewers should be carried out to the same standards as new drains and sewers (see Approved Document H1 Section 2).

    B.16 Where new pipework is connected to existing pipework, particular consideration should be given to the following points.

    a. Ensuring that the existing pipework is not damaged, for example by using proper cutting equipment.

    b. Ensuring that the resulting joint is water tight, for example by using purpose made repair couplings.

    c. Ensuring that differential settlement does not occur between the existing and new pipework, for example by proper bedding of the pipework.

    Sealing disused drains

    B.17 Disused drains or sewers provide ideal nesting sites for rats. In order to prevent this disused drains or sewers should be disconnected from the sewer system as near as possible to the point of connection. This should be done in a manner which does not damage any pipe which is still in use and ensures that the sewer system is water tight. This may be carried out, for example, by removing the pipe from a junction and placing a stopper in the branch of the junction fitting. Where the connection was to a public sewer the sewerage undertaker should be consulted.

    B.18 Drains or sewers less than 1.5m deep which are in open ground should as far as is practicable be removed. Other pipes should be sealed at both ends and at any point of connection, and grout filled to ensure that rats cannot gain access.

    B.19 Larger pipes (225mm and above) should be grout filled to prevent subsidence or damage to buildings or services in the event of collapse.

    Appendix H1-C: Adoption of sewers and connection to public sewers

    C.1 There are a number of different ways in which a sewer may become a public sewer. Drains serving only one curtilage cannot be adopted by the sewerage undertaker.

    An agreement with the sewerage undertaker to adopt sewers on completion

    C.2 Under Section 104 (Agreements to adopt sewer or sewage disposal works at future date) of the Water Industry Act 1991, a sewerage undertaker may enter into an agreement with a developer to adopt a sewer at some time in the future subject to certain conditions. In cases of dispute appeals may be made to the Director General of Water Services.

    C.3 Sewerage undertakers normally require the work to be carried out in accordance with their standards which are published in Sewers for Adoption.

    Requisition of a sewer from the sewerage undertaker

    C.4 Under Section 98 (Requisition of public sewer) of the Water Industry Act 1991, the owner or occupier of a building or proposed building or a local authority may requisition a sewer from the sewerage undertaker. The sewer is constructed by the sewerage undertaker who may use its rights of access to land. The person requisitioning the sewer may be required to contribute towards the cost of the sewer over a period of 12 years.

    Adoption by the sewerage undertaker at the request of the owner

    C.5 Under Section 102 (Adoption of sewers and disposal works) of the Water Industry Act 1991, a person may request a sewerage undertaker
    to adopt an existing sewer. The sewer should be in good condition and accessible. In cases of dispute, appeals may be made to the Director General of Water Services.

    Adoption by the sewerage undertaker at its own volition

    C.6 Under Section 102 (Adoption of sewers and disposal works) of the Water Industry Act 1991, a sewerage undertaker may decide to adopt an existing sewer of its own volition. The sewer should be in good condition and accessible. In cases of dispute, appeals may be made to the Director General of Water Services.

    Making connections to public sewers

    C.7 Under Section 106 (Right to communicate with public sewer) of the Water Industry Act 1991, the owner or occupier of a building has a right to connect to a public sewer subject to the following restrictions.

    a. Where the public sewer is designated as either a foul sewer or a surface water sewer, the right is limited to connection of foul drains or surface water drains as appropriate.

    b. The manner of the connection would not be prejudicial to the public sewer system.

    c. 21 days notice is given to the sewerage undertaker of the intention to make the connection.

    C.8 Under Section 107 (Right of undertaker to undertake making of communication with public sewers) of the Water Industry Act 1991, the sewerage undertaker may undertake the work of making the connection and recover their reasonable costs. Alternatively they may allow the developer to undertake to carry out the work under their supervision.

    C.9 Guidance on making connections to existing sewers is given in paragraphs 2.15 and 2.16.

    Drains which could be used to drain other developments

    C.10 Section 112 of the Water Industry Act 1991 enables the sewerage undertaker to require that a drain or sewer be constructed in a different manner so that it may form part of the general system of drainage. The sewerage undertaker repays the person constructing the drain or sewer the additional costs of complying with the undertaker’s requirement.

    Where land or property neighbouring the applicant’s site is likely to be developed, it would be prudent for the applicant to discuss the possibilities with the planning authority and the sewerage undertaker.

    Adoption of surface water sewers by the Highway Authority

    C.11 Under Section 37 (Highway created by dedication may become maintainable at public expense) or Section 38 (Power of highway authorities to adopt by agreement) of the Highways Act 1980, a highway authority may adopt, or agree to adopt in the future the drainage associated with a highway. Under Section 115 (Use of highway drains as sewers and vice versa) of the Water Industry Act 1991, the highway authority may agree that a highway drain may be used to drain rainwater from buildings. This power is descretionary.

    Table C1 Characteristics that should be considered when designing or laying a shared drain:sewer so that it meets the basic requirements for adoption Part H
    Table C1 Characteristics that should be considered when designing or laying a shared drain:sewer so that it meets the basic requirements for adoption Appendix H1