The Self Build Self Help Site Drains

A one-stop shop of information for people interested in self build - whether self building a complete home or undertaking an extension, renovation or modification.


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No connection to public sewerage system

If you are not able to connect to public sewerage or surface water systems then you will have to provide a septic tank or cess pit for foul water and a soakpit for surface water. Your architect will plan for these. Good sites that have information on septic tanks and cess pits are : Cleansing Service Group Ltd and serious**.

See our photo gallery for building a soakpit.

Various notes

Don't be put off if the roadside inspection chambers, to which you will conect, seem very deep - an excavator and competent driver will take it in their stride.

You will need to put in inspection chambers at each branch and change of direction - but check with your plumber, and check with the building control inspector - there may be instances where rodding points will negate the need for an inspection chamber.

Wider (450mm) inspection chambers are good for where the drains are deep, but Building Regs. dictate that they are no more than 1.2m deep. Where the drains are not so deep, consider narrower (300mm) inspection chambers, (subject to a maximum depth of 600mm) where rodding will still be convenient and the covers will not be so intrusive.

Don't forget to get the 4" to 6" connector to connect to the main sewers in the roadside inpsection chamber. As well as equal junctions, bends, slow bends and straight connectors, a number of flexible joints will come in useful. Make sure you observe the arrow on the flexible joints, showing the direction of flow.

In getting the correct fall (1 in 40 for 4" pipes) a convenient ploy is to attach a bit of 50mm Celotex to the end of a 2 metre spirit level. Using this and ensuring the bubble shows level will achieve the correct fall. For 6" pipes the required fall is 1 in 60.

If a greater fall is required then the level can be dropped quite dramatically with a back drop manhole. Although these can be built in brick, a much simpler way is to use a plastic inspection chamber. This requires a 4" hole to bored into one of the risers near the top - a 4" hole cutter will do this - we even use a masonry core drill and it works OK.

See our photo gallery for photos of backdrop manholes.

diagram of back drop manhole

click on diagram for a larger view

You will need pea gravel to bed the 4" pipes in (often called pea gravel but ask for 10mm clean stone, also known as crusher run - real pea gravel is smooth decorative gravel and very expensive). Make sure that the gravel is underneath the pipes as well as used to cover over. The pea gravel will allow for a certain amount of ground movement without destroying the integrity of the 4" pipe.

Using washing up liquid for push fit joints will ensure that the joint can be taken apart easily, should there be a problem.

The Building Control inspector will usually concentrate on the foul water drainage and will check for the correct fall, layout, material and depth used to bed the pipes, and connection to the main sewer. Quite often the inspector will be happy to see the drains in place and with some backfill around but with the top of the drains exposed, before completing the backfill - but check out his requirement at the previous inspection.

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