Introduction

Designed to carry waste water from a property to the main sewage network, domestic drainage systems are classed in 2 distinct ways. Depending on the age of your property, the drainage will be either a single-stack or a two-pipe system.

Both systems functional equally well, however the single stack system is the more prefered option as it it less prone to causing damp.

Two-pipe drainage system

Primarily found in houses built before the late 1950s, in a two-pipe system the WC waste is fed into a large diameter vertical soil pipe, seperate to the other waste water. The key features of this system are:

• WC waste is fed into a large bore soil pipe, which leads directly to the sewage network, and often runs down the outside wall of a property
• Remaining waste waters from washbasins, bath and kitchen sink etc are combined via seperate smaller bore branch pipes in a gully just below ground level
• To prevent back siphoning and to discharge any gases from the drains, the large soil pipe is vented to the outside above the guttering
• All appliances contain a u-bend trap full of water to prevent drain smells penetrating the house
• The waste from the gully finally meets the soil water a short distance from the property on its way to the sewers
• At this meeting point will be an inspection chamber with a manhole cover

The primary problems associated with two-pipe systems are centred around the gully, where the branch waste pipes meet. During winter the gully can easily become blocked with dirt and leaves, which if left unattended, can lead to penetrating damp and other damp related issues

Single-stack drainage system

Since the late 1950s, almost all new houses are built with a single-stack drainage system. The key features of this system are:

• All waste from washbasins, sinks, baths and WC waste is fed into the same large bore vertical waste pipe
• Unlike the two-pipe system, this large bore pipe is often incorporated into the internal framework of a property
• To prevent back siphoning and to discharge any gases from the drains, the soil pipe is vented to the outside above the roof line
• All appliances contain a u-bend trap full of water to prevent drain smells penetrating the house
• Exceptions to the main soil pipe can be waste from a kitchen sink, and sometimes a cloakroom WC, which will each have its own drain point
• A single-trap system needs to be designed carefully to prevent a heavy flow of water from one appliance siphoning the trap of another
• A short distance from the property will be a manhole cover over the inspection chamber for drainage to the sewer network
• If the cloakroom WC has it's own drainage point, it will have a manhole cover and inspection chamber too

Cesspools & septic tanks

When a property is situated in a remote location, it is often unfeasable to connect this property to the main sewage network. In these instances, the waste water from the property is collected in either a cesspool or a septic tank.

• Cesspools & septic tanks

Who is responsible for the drains?

If the property has it's own drainage system, then the entire system up to the point where it meets the main sewer network is the responsibility of the property owner.

If the property is connected to a communal drainage network things are not so straightforward. If the drains require maintenance or blockages to be cleared then:

• If the drains were constructed before 1937 the responsibility lies with the local council
• If the drains were constructed post 1937 the responsibility lies with the householders collectively. The cost of any repairs etc must be shared no matter where in the system

Clearing blocked pipes and drains

If water fails to drain cleanly from a washbasin, bath or sink it's advisable to address the issue as soon as possible. Chemical unblockers are a good option, however sometimes it is necessary to use a pump or plunger on sinks washbasins and WCs, and rods for drains and sewers.

• Advice for clearing pipes & drains

Further information and useful links

• Mains water systems
• More plumbing & heating topics
• Full guide to rot, infestation, damp and subsidence
• Where does damp come from? What to check
• Successfully damp proofing your home

• Find a Plumber near you
• Find a Drainage Specialist near you

• Your Local Council