Last edited 20 May 2017

Approved Document C

The first set of national building standards was introduced in 1965. Now known as the building regulations, they set out:

What qualifies as 'building work' and so fall under the control of the regulations.
What types of buildings are exempt.
The notification procedures that must be followed when starting, carrying out, and completing building work.
Requirements for specific aspects of building design and construction.

The 'approved documents' provide guidance for how the building regulations can be satisfied in common building situations. There is no obligation to adopt the solutions presented in the approved documents, the building regulations can be satisfied in other ways.

Approved Document C: Site preparation and resistance to contaminants and moisture, was last published in 2013.

It covers the weather-tightness and water-tightness of buildings, subsoil drainage, site preparation, and measures to deal with contaminated land, radon, methane, and other site related hazardous and dangerous substances.

In terms of resistance to moisture, the regulations state that the building should be protected from harmful effects caused by:

Ground moisture.
Precipitation including wind-driven spray.
Interstitial and surface condensation.
Spillage of water from, or associated with, sanitary fittings or fixed appliances.

It defines a ‘contaminant’ as ‘any substance which is or may become harmful to persons or buildings, including substances which are corrosive, explosive, flammable, radioactive or toxic’; and lists examples of sites likely to contain contaminants, including:

Animal and animal products processing works.
Asbestos works.
Ceramics and asphalt manufacturing works.
Chemical works.
Dockyards and dockland.
Gas works.
Landfill and other waste disposal sites.
Oil storage and distribution sites.
Power stations.
Scrap yards.
Sewage works.
Texile and dye works.

The content of the Approved Document includes:

Section 1: Clearance or treatment of unsuitable material – This includes guidance on various site investigation measures and types of unsuitable material.
Section 2: Resistance to contaminants – This includes risk assessment and remedial guidance on solid and liquid contaminants, methane and other gases from the ground, and radon.
Section 3: Subsoil drainage.
Section 4: Floors – This includes guidance and technical solutions for ground supported floors, suspended timber ground floors, suspended concrete ground floors, floors exposed from below, and resistance to surface condensation and mould growth.
Section 5: Walls – This includes guidance and technical solutions for internal and external walls (moisture from the ground), external walls (moisture from outside), solid external walls, cavity external walls, cavity insulation, framed external walls, cracking of external walls, impervious cladding systems, joints between doors and windows, door thresholds, and resistance of external walls to damage from interstitial condensation, surface condensation and mould growth.
Section 6: Roofs – This includes guidance and technical solutions for roof resistance to damage from moisture from outside, interstitial condensation, surface condensation and mould growth.