Last edited 08 Oct 2019

Site preparation

Before building work can commence on a site, certain activities must be taken to ensure maximum health and safety is achieved and that construction operations will not be hindered.

The requirements of the Building Regulations are set out in Part C. Approved Document C (AD C) of the Building Regulations 'Site preparation and resistance to contaminants and moisture' provides guidance for more common building applications.

The requirements of Approved Document C are as follows:

The ground to be covered by the building shall be reasonably free form any material that could damage the building or affect its stability. This requires the clearing of vegetation, topsoil and any pre-existing foundations. This can include turf and roots, especially if they are close to the proposed building and also to below-ground drainage.

Precautions should be taken to avoid danger to health and safety from contaminants in the ground and any other land associated with the building;

Installation of adequate sub-soil drainage, if it is needed, can help avoid:

Contaminants are defined as those substances which may be harmful to people or buildings, including corrosive, explosive, flammable, radioactive or toxic substances.

Some contaminants such as radon, landfill gases and those from organic solvents and fuel can penetrate the building by a variety of means. In most cases the rate of penetration can be reduced by sumps and sub-floor ventilation, as well as other ventilation strategies.

The regulations also apply where there is a material change of use, as opposed to the construction of a new building.

Sites that previously had buildings on them should be checked for the presence of old foundations, services, buried tanks and other infrastructure that could pose a danger to persons using the building and the immediate area.

Numerous solid, liquid and gaseous contaminants can arise on sites, especially those with an industrial heritage. Even agricultural sites may have pesticide, fertiliser, fuel and oil contamination that could be injurious to health. Some sites are more likely to be affected than others. The AD C (Table 2) lists examples of such sites eg gas works, landfill sites, paper and printing works etc.


Ensuring the safe development of land with potential solid and liquid contaminants will require undertaking risk assessments, of which the general concepts and recommended stages are included in AD C. Where unacceptable risks are detected, they must be managed through the appropriate remedial measures that cover treatment, containment and removal.

Methane and other gaseous contaminants are deemed hazardous and are generated either naturally or by landfill waste. These too must follow the stated risk assessment procedures.

A building’s floors, walls and roof should adequately protect the building and its users from harmful effects that may arise from:

The above is a selective summary of the site preparation required under the Approved Document C. Readers are advised to consult the document for more information. It is available online.

[edit] Related articles on Designing Buildings Wiki

[edit] External references