Waterproofing around retaining elements

150 mm

Walls and/or floors require waterproofing where structural elements like retaining walls, buried podiums, or raised external ground levels greater than 150mm create a risk of contact with groundwater

Walls and/or floors require waterproofing where structural elements like retaining walls, buried podiums, or raised external ground levels greater than 150mm create a risk of contact with groundwater. This also applies to lightwells formed by retaining walls.

Basis in regulation

BS 8102
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Part C
Approved Document C
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How to check it on site

Verify that waterproofing is correctly applied and continuous for all retaining elements, ensuring no pathways for water ingress.

Common failure

Failure to extend waterproofing sufficiently or correctly detail it at the base of retaining elements, leading to water penetration.

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

Ready-mixed concrete temperature and curing

5 °C

Ready-mixed concrete delivered to site should have a minimum temperature of 5°C, as specified in BS EN 206

Minimum

Low-Level Protection for Timber Frame and SIPs

150 mm

For closed panel timber frame and structural insulated panels (SIPs), the lowest timber element must be positioned at a minimum of 150mm above the finished ground level

Minimum

Foundation depth during cold weather

450 mm

When construction occurs in cold weather, foundations should be at least 450mm below existing ground level, or adequate measures must be taken to prevent ground freezing

Maximum

Pipe support spacing and thermal movement

110 mm

Horizontal drainage pipes, typically 110mm diameter, require support at regular intervals, often around 900mm to 1000mm centres, or at every joint/socket

Minimum

Traditional manhole construction

100 mm

Traditional manholes feature a concrete base at least 100mm thick and walls constructed from brick, blockwork, or concrete appropriate to ground conditions

Minimum

DPC and Cavity Tray Locations

150 mm

Damp-proof courses (DPCs) must be installed at the base of walls, at least 150mm above the external ground level, and linked to the damp-proof membrane (DPM) in solid floors to prevent rising damp