Everything you need to know about Twinwall Drainage Pipes. 

picture image of twinwall drainage pipe blog post

Twinwall pipe is designed to carry surface water below ground and can also be used for non-pressurised surface applications, such as a rainwater harvesting system. It is one of the most commonly installed surface water drainage systems. The pipes are made for the purpose of strength and are made using HDPE (high-density polyethylene). This type of material gives the pipes advantages such as long term reliability and freeze break resistance. The heavily structured double wall also means that common chemicals will not affect the pipe in any way, making it a safe option to be used for a range of projects in places such as; highways and airports.

At EasyMerchant we can supply both unperforated and perforated lengths to suit the area or land you are working on. Please note that 900mm is in 3m single socketed lengths, whereas the smaller sizes come in 6m lengths with no socket on the end (plain ended). The range that we hold is Ridgidrain, manufactured by Polypipe.

 Features and Benefits of twinwall drainage pipe.

blog post pictures for twinwall drainage installation

  • It is a strong yet lighter alternative to concrete (94% lighter).
  • Doesn’t allow natural chemicals to breach the pipes walls.
  • BBA,HAPAS and PADS approved.
  • The pipes can cope with movement above ground, this is why it is used for the construction of roads and places where heavy loads will be passing through.
  • The rigid outside and smooth inside allows for a better flow capacity of the water through the twin wall drainage system.

Places commonly used for the application of twinwall drainage pipes.

blog post pictures of large diameter twinwall drainage pipes

  • Highway projects
  • Railway projects
  • Airport projects
  • Network rail parts and drawing systems
  • Agricultural projects (crop ventilation)
  • Yard drainage systems
  • Landfill sites
  • Culverts ( a structure that guides water past an obstruction)

Twin wall pipe fittings

blog post image of rigidrain twinwall fittings

At EasyMerchant we hold various twinwall drain pipe fittings such as: bends, branches, sewer adaptors, couplers and pipe seals. Like the pipes, our fittings are of high quality and are approved by the following bodies; BBA, HAPAS and PADS.

Type 8 filter drain


Type 8 filter drain is also known as geotextile wrapped twinwall, fin drain and land drain including sock. The idea behind these products is to allow the pipe to be used in sandy areas etc, which may put the pipes at risk of getting blocked.

At EasyMerchant we supply the Type 8 filter drain. A filter style drain is a single wall PVCu perforated and corrugated pipe that is already wrapped in geotextile membrane. The membrane is made out of polypropylene/ polyethylene filaments which are heat sealed.

Through using the type 8 pipe it reduces the need for surrounding aggregate to be used which is advantageous when working on projects such as roads where traffic may disturb gravel and dirt etc. Along with this the pipe is able to absorb water which decreases the chance of standing water.

The correct place to install twin wall drainage pipes including types and sizes

There are many projects that you can use twinwall pipes for, however you must take into consideration the fact that the larger the diameter of the pipe, the more effective it will be in terms of water flow capacity.

For example if you are working on an agricultural project you would use 110-300mm diameter (perforated) over the bigger sizes as the bigger pipe will create dry ground. This would not be good for agricultural productivity. Nonetheless when working on more industrial based jobs, like highways and airport projects, you would go for the size’s up to 600mm diameter (unperforated).  The size of the pipe you choose is heavily dependent on the size of the job at hand.

The basics of installing twinwall drain pipes

blog post picture of twinwall drainage pipe used in culvert

Preparing your trench

The standard sizes for the trenches used range between 300mm and 600mm outside diameter, but on certain occasions there may be a need for larger trenches. The regulations in line with the excavation of land, must be followed when digging your trench. Along with the trench there must be an appropriate pipe bed where the pipe will be placed evenly.

Side filling

The recommended side filling used on most construction projects is a shingle like gravel. Enough of this must be used in order to support the size of the pipe being used.


After these steps have been completed its time for the backfilling. For this process pebbles/shingles, no larger than 50mm, must be compacted after a cover depth of 300mm is achieved. Once this has been achieved the trench can be covered with a material suitable for your project.

What’s the difference between twin wall drainage and land drainage?

land drainage coils

Twinwall pipe is different to land drain pipe because it is rigid and can not be bent. The key reason for this is that the pipes come in a variety of sizes and diameters and the bigger they are the heavier they must be in order to support the excess covering placed over it during the backfill process. They tend to be bigger because they are more frequently used for industrial based builds.

On the other hand, land drainage has the ability to bend and is lightweight, meaning that it can be manoeuvred far easier than twin wall pipes. It is also single walled HDPE, which comes in both unperforated and perforated. However, unlike drain twinwall pipe, land drain is mostly used for sports fields and agricultural land.

These are the key differences between the two types of pipes, both can be purchased at EasyMerchant.co.uk. If you still have questions regarding twinwall drainage pipe, feel free to ring us and we will be happy to help.

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