Quality.
    Minimum
    England

    Ground drainage pipe support

    100 mm

    Underground drainage pipes require proper support, either on a minimum 100mm deep granular bed or a carefully hand-trimmed trench bottom

    Underground drainage pipes require proper support, either on a minimum 100mm deep granular bed or a carefully hand-trimmed trench bottom. Avoid using hard, temporary supports like bricks, which create rigid points and can deform the pipe run. Pipes under suspended floors in areas of potential ground movement need additional design considerations.

    Basis in regulation

    How to check it on site

    Verify that pipes are laid on specified granular bedding or a suitably prepared trench bottom, free from hard spots.

    Common failure

    Use of inappropriate or temporary supports leading to hard spots and pipe distortion or failure.

    Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

    Related dimensions at this stage

    Minimum

    Gradient of a 100 mm foul drain

    1 in 80 (steeper for runs with fewer appliances)

    100 mm foul drain serving at least one WC

    Minimum

    Depth of cover to a buried drain

    600 mm under gardens and other areas not subject to vehicles; 900 mm under roads and driveways

    Buried foul or surface water drain outside the building footprint

    Minimum

    Distance from a soakaway to a building

    5 m

    Surface water soakaway serving a dwelling

    Minimum

    Height of a ventilating stack terminal above an opening

    900 mm above the top of any opening within 3 m horizontally

    Open ventilating stack terminating at roof level or on an external wall

    Maximum

    Spacing between drainage access points

    45 m

    Straight run of buried drain between access points

    exact

    Backfill compaction protocols

    300 mm

    Trench backfill must be well compacted in layers no deeper than 300mm to achieve stable ground

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