Where do I need inspection chambers on a sewer connection?

Inspection chambers (ICs) are required at every change of direction, change of gradient, junction between two or more drains, and at intervals not exceeding 45 metres on straight runs. You also need an IC at the head of the run and within 12m of the public sewer connection point. All chambers must be accessible for rodding.

What is the minimum cover depth for a sewer pipe?

Under Part H, minimum cover depends on location: 600mm under gardens and footpaths, 900mm under driveways and light traffic areas, and 1200mm under roads with heavy traffic. If you can't achieve minimum cover, concrete protection or ductile iron pipe may be needed.

What bedding class do I need for sewer pipes?

Class D (granular bedding with pea gravel) is the most common for domestic connections. It provides good support with 100mm bed under the pipe and gravel to 300mm above. Class S (full concrete surround) is used where cover is shallow or loads are high. Class N uses the natural trench bottom where soil conditions are suitable.

How do I connect to the public sewer?

You need a Section 106 sewer connection agreement from your local water company. They will specify the connection point, method and supervise the connection. A build-over agreement is needed if building within 3 metres of a public sewer. The connection is usually made via a saddle connection or new manhole.

What pipe diameter is needed for a domestic sewer connection?

Most domestic foul drainage uses 110mm (4-inch) uPVC pipe. This is adequate for up to about 20 dwellings on a single branch. Surface water drains also typically use 110mm, though 160mm may be needed for larger catchment areas. The public sewer main is usually 150mm or larger.

TradeCalculator

Sewer Connection Calculator — Pipe Run, Chambers & Bedding

Calculate pipe lengths, inspection chamber positions, bedding material and cover levels for a new sewer connection to Part H and Sewers for Adoption.

Total Pipe Length

Total run from building to sewer connection

Average Pipe Depth

Average depth from ground to pipe invert

Number of Bends

Each bend needs an inspection chamber

Number of Junctions

Where branch drains join the main run

Bedding Type

Cover Class

Price Per Metre (optional)

Installed cost per metre including pipe, bedding and backfill

How We Calculate This

This calculator plans your sewer connection by determining inspection chamber positions, trench volumes and bedding requirements based on your pipe run.

The formula

Inspection Chambers = Bends + Junctions + floor(Length/45) + 2 (head & tail)

Trench Volume = Length × Width × Depth

Bedding Volume = Length × Width × (0.1 × Bedding Factor)

Cover depth checks

A15 pedestrian: min 600mm cover
B125 light traffic: min 900mm cover
D400 highway: min 1200mm cover

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.