What This Requirement Covers
Approved Document C1 requires that the ground to be covered by a building is reasonably free from any material that might damage the building or present a risk to health. This includes naturally occurring contaminants (radon, methane), man-made contamination (from previous industrial use), and vegetation.
Key Requirements
Contaminants
- The site must be investigated for contamination where there is reason to suspect it (e.g., previous industrial use, landfill, fuel storage)
- Assessment follows the CLR11 framework (Model Procedures for the Management of Land Contamination)
- If contamination is found, a remediation strategy must be agreed with the local authority and implemented before construction
- Common contaminants include hydrocarbons, heavy metals, asbestos, and landfill gas
Radon
- Radon is a naturally occurring radioactive gas that can accumulate in buildings
- The need for radon protection depends on the location (radon-affected areas are mapped by Public Health England)
- Basic radon protection: A radon-proof membrane across the ground floor, sealed at joints and edges
- Full radon protection: A radon-proof membrane plus a radon sump (passive or active extraction) to collect and discharge radon gas
Vegetation
- Trees and vegetation must be cleared from the building footprint
- Tree roots must be removed to prevent future heave or settlement
- On shrinkable clay soils, the proximity of trees to the building affects foundation depth requirements
Subsoil Drainage
- Where the water table is high or the ground is prone to waterlogging, subsoil drainage must be provided
- Land drains (perforated pipes in granular trenches) divert groundwater away from the building
- Subsoil drainage must discharge to a suitable outfall (ditch, soakaway, or surface water drain)
Practical Compliance Tips
- Commission a Phase 1 desk study and, if necessary, Phase 2 intrusive investigation before purchasing development land
- Budget for remediation costs if contamination is identified; costs can be significant for heavily contaminated sites
- Check the radon risk for the site using the Public Health England radon maps and specify the appropriate level of protection
- Remove all vegetation, topsoil, and organic material from the building footprint before constructing foundations
- Install subsoil drainage during foundation construction; retrofitting is much more difficult
- Keep contamination assessment reports, remediation verification reports, and radon protection details for the building file
- If the site has a history of landfill or industrial use, consult the Environment Agency for additional guidance