A beginners guide to inspection chambers

A beginners guide to inspection chambers

So you know you need to install an inspection chamber but you have a few questions, such as what’s its actual purpose and what’s the difference between adoptable and non-adoptable inspection chambers. To bring you up to speed, we’ve put together this useful guide.

What is an inspection chamber?

An inspection chamber, which is commonly known as a manhole cover, is integral to an underground drainage system. It provides an access point to enable drains to be cleaned, cleared and inspected when required.

Inspection chambers are also used for safety purposes by preventing people from entering drainage systems without authorisation. In scenarios where access is needed, ‘confined space’ risk assessments and method statements must be prepared.

Manhole and inspection chamber guidance is governed by Building Regulations.

When should you use an inspection chamber?

You will typically need to use an inspection chamber in the following instances:

  • Where a branch pipe joins a main drainage run in the system
  • When there is a straight run of piping over 22 metres long
  • When a drain changes direction horizontally by more than 30 degrees
  • When there is a change in pipe size

A key tip when installing a chamber though is to remember you will need to get a drain rod in every single part of the drainage system. If there is ever a blockage you, will need to be able to do this!

What is the structure of an inspection chamber?

An inspection chamber is sectional and typically consists of a base, sectional risers with a seal, and a manhole cover in your desired finish. The risers sit on top of the base and the joint is sealed using an integral rubber seal. Subsequent risers can also be added to provide further height and sealed using an integral rubber seal again. The cover and frame sit on top of the risers at ground level.

What’s the difference between an adoptable and non-adoptable inspection chamber?

Typically, a chamber that serves two or more properties and connects to the UK public sewerage network is considered an adoptable inspection chamber. This may, however, vary depending on your local water requirements.

In contrast, non-adoptable inspection chambers are deemed to typically serve just one property and remain the responsibility of each householder.

What are the choice of manhole covers?

Manhole covers come in a range of different shapes, sizes and materials. These include square, round, plastic, steel, recessed for block paving or slabs, and airtight covers for internal use. At Cotterill Civils, we provide a wide variety of manhole cover to suit your specific requirements.

The specification of manhole and access covers for public areas is laid down in BS EN124, which is shown in the table below.

How deep should an inspection chamber go?

This depends on the size of chamber. There are generally two sizes of chambers: 450mm and 320mm in diameter. With the smaller chambers (320mm diameter) you can only use them to a depth of 600mm. If you go any deeper, it then becomes impossible to bend a drain rod when you come to inspect it for blockages. In contrast, the larger chambers (450mm) can be installed to a depth of 1.2m, although you can go down as far as 3m if you use a restricted access cover.

Should a chamber be concreted in?

According to regulations inspection chambers should be installed on suitable bedding material. If the trench is stable, it is advised that you install them on a bed of pea shingle around 150-200mm deep, and then use the pea shingle again to back-fill around it.

Why are manholes and sewers considered dangerous?

Manholes and sewers are considered to be exceptionally dangerous places. This is because noxious gases can be present that can injure and even kill. It is recommended that any work on live sewers is undertaken by drainage specialist who have completed a ‘Confined Spaces’ and/or ‘Sewer Working’ safety course.

What is a catchpit?

A catchpit is an empty chamber that is installed into a drainage system to prevent silt and debris from building up and causing blockages.

Where can I get expert advice on inspection chambers?

At Cotterill Civils we supply a wide range of inspection chamber to suit your specific need and can provide you with expert advice on a solution to meet your needs.

Call us today for expert advice: 0121 351 3230.


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