Underground Drainage - Laying and Installing (2023)

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Guide to providing advice on underground drainage including the laying and installation of underground drainage pipes and systems, what you need to consider when laying or replacing drainage pipes, the different types of pipework available, how to dig your trench and the safety requirements involved, how to backfill a ditch and what laws and regulations are involved.

If you need to locate existing soil drainage runs on your property, the first place you look for help is your title deed. These may include information about existing underground drainage routes or changes made over the years.

You must also find out if your existing drainage was installed before or after October 1, 1937 by reference to the Public Health Act 1936. After that date, the law changed as to who is responsible for the maintenance of these underground drainage sections. You don't want to pay for drain repairs that you are not responsible for!

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If you are creating new underground drainage runs, or remodeling or altering existing "runs", you have a legal obligation to notify your local building control authority. You must provide them with drawings of your proposed work and have your work checked by a building inspector.

If you're just replacing an existing damaged underground drainage system, you don't need to contact your building control authority.

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Selection of pipes for underground drainage

There are many types of pipes for use with underground drainage such as: B. uPVC, concrete, stoneware, cast iron, glass fiber reinforced plastic (GRP) and asbestos. Some are no longer used for obvious reasons. It is important to note that underground drains are always brown in color while above-ground drains are gray or black.

Most homes/property in the UK have used two types of pipe for underground drainage, Clay & Plastic UPVC since the late 1970's. The latter has become cheaper and more popular.

The use of vitrified clay pipes is recommended in regions in which ground movements occur or may occur due to topography, precipitation and climate. This form has greater structural strength and is not as dependent on the backfill materials, which are the structural part of the underground drainage system, known as Class D bedding.

The connection of the older clay pipes with newer plastic pipes can be achieved with a clay-plastic coupling shown on the left. These and all other whistles etc can be purchased by clicking on the tool shop pictures at the bottom of the page.

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All stretches of plastic pipe must be cased with a 10mm layer of pea shingle or a mixture of fine gravel before larger material can be placed on top for compaction and then receive the top layer of backfill.

Note:If you are replacing old damaged underground drain pipes, some hardware stores have inventory or can purchase old imperial sizes of pipe. Imperial to metric conversion adapters are also available.

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There are two types of pipe sections you will use; either straight connection or socket format, i. H. Male to female, with the female portion always being the lower part of the barrel.

Most modern pipe runs are now straight connection types with a collar connector - see below.

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What types of pipes to use

Plastic tube (uPVC) 110 mm

The obvious benefit of using plastic tubing is ease of use as it is lighter and can accommodate longer runs of tubing, reducing the need for connectors. Plastic pipes are available in lengths of 3 m and 6 m. Plastic tubing runs can be ribbed and do not allow much flexibility.

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Plastic tubing only requires the use of a hacksaw to cut the tubing. But don't let that fool you, sometimes it's difficult to get a straight cut on a large diameter plastic pipe with a hacksaw. It's often easier to use a cheap wood saw to get a straight cut.

If you are installing plastic pipe during the winter months, take your time cutting the pipe as the lower temperatures make it more brittle and therefore more prone to breakage or cracking.

You'll have to file the cut edge anyway to create a chamfer to make it easier to pick up the connector with a lubricant; a simple action as shown in the PDF below supporting this project. Many drain layers use fairy liquid as a lubricant to connect pipes, but we recommend you use a proprietary compound.

The cheapness of plastic pipe can sometimes be deceiving as you will incur a higher cost with the specified backfill materials than with the backfill materials required for vitrified pipe sections.

Stoneware pipe: (100 mm)

This is available in lengths of up to 2m, is heavier and more stable to process than plastic. It requires less expensive materials for support and backfill and plays a big role in its more environmentally friendly properties in the manufacturing process compared to plastic pipes. This makes clay whistles very popular with large construction projects and companies.

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Other advantages of clay whistles are that they are more stable under the pressure of soil weight mass from above and have a flavor not enjoyed by rodent society unlike plastic whistles! It can also withstand more modern methods of underground high-pressure pipe cleaning that plastic cannot.

However, VCP requires more substantial cutting tools, such as B. clay pipe cutter. These wrap around the pipe and increase even pressure until they create a straight fracture cut, and even power saws or grinders can be used to create a straight cut. Extreme caution should always be exercised when using a high-speed cutter.

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Special care is required when cutting as clay pipes can be fragile prior to installation.

As with plastic tubing, the use of clay tubing requires lubrication to facilitate the mating of sections and connectors. These come in either liquid or jelly form.

Digging a trench for underground drainage

Before you can proceed with the pipe laying, you need to dig your trench. It is best not to dig the proposed trench too far ahead of pipe laying. Rain and overnight weather conditions can cause your trench to collapse or fill with rainwater and unless you have pre-dug a sump hole this can halt all work.

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Safety requirements for digging trenches

  • If your trench is deeper than 1200mm (4ft) it will need to be stabilizedby law!
  • Never work alone in ditches
  • Don't leave your trench open for too long, the sides could collapse or fill with rainwater
  • Make sure your excavated trench is fenced off from people, children, and pets
  • Keep your ditch widths to a minimum to prevent side collapse (300mm plus the width of the ditch).
  • Do not dig trenches in bad weather
  • Do not stand near the edge of the ditch and if you cannot brace yourself, back the top of the ditch 45 degrees to stay safe

When you run a straight run of pipe, you have a start and end point for your run. You can connect a plumb line between these two points, which will give you an accurate guide to how much foundation bedding to put in your trench before you start laying pipe.

More modern methods of checking levels/gradientscan be checked with a laser leveloder other Nivellierinstrumente.

Minimum slope requirements:

  • Surface drainage = 1:100 (10mm slope per meter)
  • Dirty water drain = 1:40 (1:80 with attached toilet) (25mm height gradient per meter)
  • Laying a string of tubing is a simple, iterative process as follows;
  • Lubricate the fitting and tube
  • Slide connector onto pipe
  • Lubricate the pickup fitting and open end of the tube
  • Push the next piece of pipe into the connector

At what depth should underground drainage pipes be laid?

There is no prescribed minimum depth, simply because there is always an "end point" where each pipe opens out.

It is the depth of this endpoint that determines the depth of any access chamber leading to it.

Required access points for the new underground drainage run

Whenever you install a new underground drainage route, you will need inspection manholes, manholes, roding eyes and access fittings so that all blockages can be accessed and removed.

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These elements must be installed to allow access at points of your new underground drainage when:

  • head of your new run
  • Any change of direction
  • Increasing or decreasing the pipe size
  • Any branch in your new drainage canal that is not accessible from another access point
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No specific distance between wells is prescribed, except that no part of a pipe should be more than 50 m from an inspection chamber.

If maximum manhole spacing is to be employed, it is recommended that pole grommets be installed every 22m or so.

This means that all pipes are accessible from at least one point every 22-25m where blockages can be pushed into an access chamber.

Backfill your ditch

Once you have finished installing your new underground drainage route and tested for possible leaks, you can start backfilling your trench with the right materials:

For the use of plastic underground drain pipes….

You already have 10mm pea shingles or 14-5mm stepped shingles as bedding for your plastic pipe cover up to the top of your plastic pipe.

Next you need to lay a 100mm thick cover of selected fill or granular material when backfilling your trench and finally backfill with a layer of selected backfill containing no stones over 40mm, no lumps of clay over 100mm and no frozen material contains.

The last layer can be compacted when laying in the trench.

For clay underground drainage pipes….

Again, you have the bedding layer of shingles or stepped shingles that your clay pipe run will sit in.

You don't have to completely cover your clay pipe with this layer. A minimum cover halfway up the stoneware pipe is sufficient.

You can then complete your backfill with a selected fill containing no stones over 40mm, no lumps of clay over 100mm and no organic matter or frozen materials.

note: Pipes laid at depths of less than 600mm which do not pass under a road should be protected from damage if necessary by laying a layer of concrete, paving slabs or similar over them. A damping layer of granular material at least 75 mm thick must be laid between pipes and plates or concrete.

For clarification; where required means that the pipe is in some way susceptible to breakage or failure. Malfunctions, cracks and fractures can lead to deposits and blockages.

All project content written and produced byMike Edwards, founder of DIY Doctor and industry expert for building technology.


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