This information has been provided by Professional Building Supplies a leading UK seller of guttering supplies, who also sell a range of eco building products.

This is a general guide on how to lay 110mm PVC underground drainage pipes. Please note: any installation must be planned and tested in accordance with regulations from your Local Authority.

Any installation should always be carefully planned before any work is carried out. This involves checking that you have all the tools required and ideally all materials are ready to use on site. Therefore the drainage trench shouldn’t be dug until everything else is ready as the drainage trench should only be open for as short a period as possible. This is because the longer it is open the higher the risk is of the sides and bottom of the excavation being damaged by uncontrollable factors including: weather conditions, pedestrian traffic and animal activity. The trench must be wider than the pipe diameter by at least 300mm; subsequently whilst laying the 110mm drainage pipe the trench shouldn’t be any narrower than 410mm.



‘As-dug material’ is the soil that has been dug out from the trench. If the as-dug material has no flints or stones bigger than 20mm then the bottom of the trench can be appropriately trimmed allowing the pipe to be laid directly in the trench. You can use the as-dug material as sidefill material surrounding the pipe; this must be compacted together and cover the whole pipe. Ensure you sidefill equal amounts on either side of the pipe as uneven sidefill on one side could cause the installation to move position.

If the as-dug material is not suitable then a granular material should be used to form the bed and the sidefill in the trench. A good granular material is pea shingle which can be bought from building suppliers and garden centres. The particles in this granular material should not be larger than 10mm. When using a granular material such as pea shingle, the trench should be excavated to a depth that allows for at least 50mm of bedding – and up to 100mm if the condition of the soil is poor.

The pipes should be laid to a gradient minimum of 1 in 40 or a minimum of 1 in 80 if there are five or more WC’s which will be connected to the pipeline. Ensure pipes are laid in the centre of the trench with equal sidefill. A small depression should be made to accommodate pipes and fittings and the whole installation should be totally supported for its entire length.

When the installation has been tested you can backfill the trench with the as-dug material. If the as-dug material has stones larger than 40mm then use granular material to fill the 100mm of backfill over the top of the pipe. You can sieve the as-dug material and then use it as backfill once all large stones are removed. If your installation has a depth that is greater than 2m or the ground condition is poor then granular material should be used for the first 300m of backfill. If the installation is less than 600mm you must protect the pipe from damage by laying paving slabs above the pipe. Here you should lay at least 75mm of granular material between the slabs and the pipe.

Professional Building Supplies is a leading UK supplier of building materials including: cast iron guttering, underground drainage, manhole covers, plumbing materials, eco building products and general guttering supplies. Visit the website more for information: http://www.professionabuildingsupplies.co.uk.