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Installing pipes: an intro to the principles of underground drainage

When it comes to installing pipes underground, understanding the principles and how to initially prepare your plastic pipe is important, as it ensures your system will be secure and safe from leaks or other damage.

You will undoubtedly need to cut and join pipes together. A plastic pipe can be easily cut with a standard hacksaw, provided it is fine-toothed enough. Any time a pipe is cut, the end must be cleaned of any dirt, grit or stray plastic (known as chamfering). This can be achieved with a medium file. When connecting the chamfered end of a pipe, the ring seal should be lubricated. Ensure the pipe is “flush” to the fitting before pushing it in fully to complete the joint.

Laying your underground drainage pipes

Underground drainage pipes should ideally be laid in a trench which measures 300mm wider than the pipe itself (for example, a 110mm pipe would require a trench of at least 410mm). If the trench is made from a suitable material and contains no large stones or flints, it can be trimmed and used as the pipe bed – otherwise a granular material such as small shingles should be used for the bed. Material which has been excavated to create the bed can be used as backfill/sidefill, and the pipe should be covered by at least 300mm of material before any mechanical compaction is undertaken.

Avoiding pipe damage

If your underground drainage pipe is in an area where it is in danger of being damaged (such as near a garden area or vegetable patch), it is a good idea to cover it with paving slabs as a reminder not to dig too closely to it.

Understanding pipe falls

Most domestic properties make use of 110mm underground drainage pipes. In homes with five or less bathrooms, the system should be laid to a 1-in-40 fall. This fall must not be exceeded, as it allows the system to remain self-cleaning. In the rare occasion that more than five bathrooms are connected to one system, it is advisable to contact your local authority for further advice.

For further information on underground drainage, or for help and advice on the right materials for the job, why not contact our team today?

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