PART C · Site preparation and moisture
Part C building regulations explained
Part C deals with the ground beneath a building and protection against moisture. It covers site preparation, contaminants and moisture reaching the building through the ground or its external fabric. These issues should be considered before construction details are finalised.
What does Part C cover
Requirement C1 addresses site preparation and resistance to contaminants. C2 addresses moisture in floors, walls and roofs, including relevant risks from condensation.
Approved Document C describes recognised approaches for matters such as damp proofing, ground gases and subsoil drainage. The appropriate measures depend on the site and construction.
Why site history matters
A clear plot is not necessarily clean ground. Former industrial use, buried waste or previous structures may justify investigation. Ground gas risks also vary by location and local conditions.
Ask what information supports the proposed design. Where a risk is identified, obtain a suitable assessment rather than relying on a standard detail without explanation.
How does moisture protection work
Damp proof courses, membranes, drainage, cavities and ventilation can form parts of a coordinated system. Their junctions matter. A membrane in a new floor is less useful if its connection to the wall protection is left unresolved.
For example, an extension meeting an older house needs a clear detail at the junction between new and existing construction.
Does Part C solve every damp problem
No single measure does. A stain can result from rain penetration, leaks, condensation or ground moisture. Establish the cause before selecting a repair.
Part F ventilation and Part L insulation may also affect moisture behaviour. Improving one element without considering the others can leave an avoidable problem.
Before work is covered, inspect and record critical membrane and damp proofing connections. Keep the site assessment and construction details with the project records.