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Drainage and Sewers

Article 385 [ added on 30-03-2010, updated on 03-06-2010 ]

Planning Permission  

If you need to carry out repairs or maintenance on drainpipes, drains or sewers, Planning Permission is not usually needed as drains, sewers and manholes are often shared, it is recommended that clarification of ownership and responsibility is sought before carrying out any changes.

If the dwelling is situated in a “designated area” i.e. Conservation Area, Listed Building, National Park or Area of Outstanding Natural Beauty, Planning and other permissions may be required.

Building Regulations

Drainage & Sewers come under the section Part H - Drainage and waste disposal in the Approved Documents of the Building Regulations.

If repairs or replacements of existing drainpipes or manholes are like for like; Building Regulations are not usually required.
Approval is required for the provision of a new drain, manhole or associated fitting. Building Regulations will also apply to non-mains foul sewerage facilities (such as septic tanks), including outlets and drainage fields. They will also apply to new rainwater or foul drains inside and outside of a building.

Foul Drainage

•    Foul Drainage includes all foul pipe work up to the point of connection with the sewer/septic tank etc.
•    Any pipe work serving more than 10 dwellings must be at least150mm in diameter.
•    Drains which serve hot food premises must have grease separators.
•    Drains which connect to existing pipe work (other than at a manhole) must use prefabrication units to avoid the use of ‘saddles’. If this is unavoidable, the whole in the existing pipe needs to be drilled rather than broken out.
•    New provisions are introduced to limit the effects of surcharging drains to prevent the foul sewage entering properties (particularly basements) in the event of flooding etc.
•    When planning drainage layouts for new developments, private (i.e. drains that serve more than one property) and public sewers must be positioned to make reasonable allowance for the potential of future extensions without needing to build over the sewer.
•    ‘Rocker pipes’ must be used for drains passing through walls or the hole around the drain must be filled with compressible material. This is in addition to the rigid sheet material already required each side.
•    On re-development sites, rodent control must be taken into account. This may include sealed inspection chambers, intercepting traps, specialist rodent barriers and solid gully covers.
•    In cases where both foul and surface water sewers are available, care should be taken to avoid cross contamination.

Wastewater Treatment Systems and Cesspools 

•    Septic tanks must have a minimum capacity of 2700 litres (4 people) plus 180 litres for each extra person.
•    Cesspools must have a minimum capacity of 18,000 litres (2 people) plus 6,800 litres for each extra person.
•    Septic tanks and cesspools must be sited at least 7m from the habitable part of any building, within 30m of a suitable tanker access and be capable of being emptied without the need for a hose to pass through the building.
•    A notice must be put up within the building describing the system, emptying details and legal responsibilities.
•    The  regulations cover the outfall drainage from septic tanks. They must be 15m from any building, 10m away from any watercourse, away from soakaways and not be covered by drives, roads or paved areas. The outfall drainage system must be designed following a percolation test and is likely that consent from the Environment Agency will also be required.

There are two types of drainage systems:

•    Surface water – rainwater from roofs and paved surfaces etc.
•    Foul – waste water from bathrooms and kitchens etc.

These two systems are sometimes combined, whereby both surface water and foul drainage are conveyed by the same drains and sewers. Do not to assume what type of system exists; instead check with the local authority or relevant water authority.

Surface Water/Rainwater

Where a combined drainage system exists, rainwater may be able to be drained into that system. If a combined system does not exist or the authorities advise that the existing drainage network has insufficient capacity for additional surface water, an alternative approach should be adopted. One option would be to use a ‘soakaway’, which is essentially a hole dug in the ground and then filled with porous material (rubble, stones etc) into which the rainwater can be drained.

Foul and Surface Water Disposal

Drainage systems should be designed to connect to a suitable outfall.

Connection to a Main Foul Sewer

All connections to a public sewer require the agreement of the responsible authority. They should be consulted as to the type and position of the connection to be made.

All connections to a private sewer require the agreement of the owners of the sewer. This should be obtained during the design process. If the main private sewer discharges into a public sewer, the local sewerage authority should be notified of the proposal.

Connection to a Cesspool or a Septic Tank

The entry flow velocity should be restricted to reduce disturbance in the tank. For drains not exceeding 150mm diameter a gradient not steeper than 1:50 for a distance of at least 12m upstream of the entry is required.

Roding and cleaning facilities should be provided at the connection with the tank.

Connection to Surface Water Disposal Systems

Surface water drainage generally needs to be separated from foul water drainage. Surface water may be discharged into public surface water main drains or directly into natural watercourses, ponds or soakaways, as appropriate. Surface water should not discharge to a septic tank or cesspool, or a separate foul sewer.

Ground Water Drainage

Ground water drainage should be designed to convey excess ground water to a suitable outfall.

Layout of Pipes

Depending on site contours and ground conditions, ground water drainage, where required, may be designed as a:

•    Natural system
•    Herringbone system
•    Grid system
•    Fan-shaped system
•    Moat system


Cesspools shall be sited and constructed to prevent contamination of water and health hazards. They should be impermeable to their contents and to subsoil water. They may be constructed of brickwork, concrete, glass reinforced concrete, glass reinforced plastics or steel.

Brickwork should be of engineering bricks laid in cement mortar and at least 220mm nominal thickness.

Cover and Ventilation

Cesspools should be covered and well ventilated.

Access and Inspection

Cesspools should be sited at least 7m from a dwelling but within 30m of a vehicle access to facilitate emptying. They should be provided with access for emptying or cleaning. All such access points should have no dimension less than 600mm and be provided with lockable covers.

Cesspools should have no openings except the inlet, the vent and the inspection access.

Septic Tanks

Septic tanks shall be sited and constructed to prevent contamination of water and health hazards.

Outfall Disposal

Satisfactory outfall disposal is essential where septic tank sewage disposal is installed. Environment Agency consent may be needed in England and Wales. In Northern Ireland the Environment and Heritage Service should approve proposals and in Scotland the Scottish Environment Protection Agency.


Septic tanks should be sited taking into account of topography to ensure that water is drained away from the building.

Impermeable to Liquids

Septic tanks should be impermeable to their contents and to sub-soil water. They may be constructed of brickwork, concrete, glass reinforced concrete, glass reinforced plastics or steel.

Brickwork should be of engineering bricks laid in cement mortar and at least 220mm thick. In-situ concrete should be at least 150mm thick.

Cover and Ventilation

Septic tanks should be covered and ventilated

Siting, Inspection and Access

Septic tanks should be sited at least 7m from a dwelling but within 30m of a vehicle access to facilitate emptying. In Scotland they should be at least 5m from a dwelling and a boundary. Septic tanks should be provided with access for emptying or de-sludging and cleaning.

The inlet and outlet of septic tanks should be provided with access for inspection.

Velocity of Flow

Provision should be made to limit the velocity of the flow to a septic tank. For drains up to 150mm diameter, the velocity may be limited by laying the last 12m of the incoming drain at a gradient not steeper the 1:50. A dip pipe should be provided with the top limb rising above scum level and the bottom limb extending about 450mm below top water level.


All foul and, where appropriate, surface water drainage systems need to be tested prior to handover.

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