Building Regulations Approved Document C

Household waste disposal has been n ongoing issue in the UK, leading to numerous disused landfill sites now being reclaimed for construction. This is where Approved Document C of the Building Regulations is crucial.

When building on potentially contaminated land, like old scrap yards or former landfill sites, it’s essential to remove or neutralise any harmful substances present in the soil. Over time, these sites can accumulate hazardous gases like methane and radon, which must be safely managed before construction can begin.

Approved Document C focuses on ensuring construction sites are properly prepared to resist moisture and contaminants. It is divided into two key sections:

• C1 – Site preparation and resistance to contaminants
• C2 – Moisture resistance on construction sites

C1: Site Preparation and Contaminant Resistance

The first section of Approved Document C focuses on three key safety measures for the sub-soil and ground beneath a construction site:

• C1(1): Ensure the building area is clear of anything that could affect stability, such as topsoil, vegetation, or old foundations.
• C1(2): If the site contains contaminants, they must be removed or treated to prevent health and safety risks.
• C1(3): Install proper drainage in the sub-soil to prevent ground moisture from entering the building and to remove any water-borne contaminants that could damage the foundation.

There is one further sub-section to part C1 and this is sub-section (4). This clarifies the term “contaminant”, defining it as any substance that could harm the building or pose risks to people nearby. This includes toxic, flammable, radioactive, and corrosive materials.

Landowners or developers should conduct thorough research before purchasing land and perform a detailed site survey during the planning process to identify any potential contamination risks. If contaminants are detected, it’s essential to consult your local building control department for guidance on making the site safe for construction.

Guidelines for handling contaminated land are set by the Town and Country Planning Acts and your local authority, which follows the National Planning Framework. Depending on the severity, agencies like Environmental Protection and the Environment Agency may also get involved to ensure safety standards are met.

Key authorities involved in addressing site contamination include:

• District Council Environmental Health Department: Notify them if you discover unreported contamination or if it spreads to neighbouring land. They should also be alerted if the actual contaminants differ from what was previously identified.
• Local Planning Authority: For contaminated plots, redevelopment is often preferred due to the high costs of resolving issues with existing structures. Any land contamination details must be included in the planning application documents. If changes to the design affect contamination management, the planning authority must be informed.
• Environment Agency: Responsible for protecting water quality and managing waste, they ensure that contaminants do not pollute water sources. They must be informed about the methods used to remove, contain, or treat contaminants and where the waste is safely disposed of.

Site investigations typically follow four stages:

• Initial Planning: Define the investigation’s goals, required information, and scope.
• Desktop Investigation: Review available data on the land’s geology, history, and environmental factors.
• Site Visit or Survey: Inspect the site to identify existing or potential hazards and plan the main investigation.
• Main Report and Investigation: Conduct soil sampling and testing to guide construction and design decisions.

Since every site is unique, these steps may vary and be tailored to the specific location and conditions.

Treating Contaminated Ground

Contaminated land can be treated using various methods, including biological, chemical, and physical treatments. These methods aim to reduce the contamination’s toxicity, concentration, mass, or spread.

The best treatment depends on the type, location, and concentration of the contaminant. Expert advice is essential to choose the right approach.

Generally, contamination is either contained or removed. Containment often involves covering the contaminated area to stop its spread. This can include layering materials to reduce contamination or improve the ground’s stability. In some cases, the construction of foundations can help manage contamination. For detailed guidance on containment, refer to the Construction Industry Research and Information Association (CIRIA) report.

If removal is needed, contaminated material is excavated, sometimes to a certain depth before covering the area with clean fill. New fill must be tested for suitability before replacement.

For more specific risk details, see Section 2.23 of Approved Document A, which outlines the procedures and considerations for addressing contamination.

• Aggressive Substances: This includes organic and inorganic acids, alkalis, and chemicals like chlorides and sulphates, which can damage materials such as plastic, metal, and concrete.
• Combustible Fill: Materials like coal, plastic, domestic waste, or ground contaminated with flammable liquids (e.g., petrol) can ignite, potentially causing underground fires that threaten building foundations and stability.
• Expansive Slags: Slag from steel production or blast furnaces can expand over time, especially with moisture. This can lead to ground movement that damages nearby buildings.
• Floodwater Contamination: In flood-prone areas, floodwaters can carry contaminants like sewage or waste, which can infiltrate buildings and properties.

Methane and Gas in the Ground

Gases, including methane, can be found in the ground due to waste in landfill sites or naturally occurring sources like peat. This does not include volatile organic compounds (VOCs).

In landfills, methane is produced as microorganisms break down organic materials, along with some carbon dioxide. Peat-rich soils can also generate methane.

If your site is in an area with these conditions, a site inspection and risk assessment are essential to determine the gas levels and their potential impact on any buildings or properties.

For domestic properties, gas-related guidelines apply in two key areas:

• Gas entering the property from the ground, which can build up inside and pose a health risk.
• Exposure in outdoor areas, including gardens and outbuildings like sheds or extensions.

If gas levels are found to be too high, this must be addressed during the planning and design phase. Depending on the severity, solutions may target specific areas or the entire site.

Common solutions include:

• Removing contaminated soil.
• Installing gas-proof barriers or membranes.
• Adding ventilation to safely release gas into the atmosphere.

Radon

Radon is a naturally occurring, radioactive gas found in areas with traces of Uranium and Radium. It is colourless and odourless, making it undetectable without a professional Radon risk report.

Radon is most commonly found in the West Country of the UK, where high levels can be present. The gas rises from the ground into buildings, posing a potential health risk that requires mitigation.

Radon-affected areas in the UK are listed in the BRE Report BR 211. However, if high levels are suspected, a Radon Risk Report is recommended. These reports can be obtained from:

• UK Radon – www.ukradon.org
• BSG Georeports – www.shop.bsg.ac.uk
• Public Health England – radon@phe.gov.uk

For workplace protection, consult the Health and Safety Executive at www.hse.gov.uk/radiation/ionising/radon.htm.

Vegetation and Trees

Before construction, the building site must be cleared to a depth that prevents regrowth. Tree roots can damage foundations, disrupt drainage, and affect the overall stability of the structure.

Existing mature trees near the site should be assessed for potential damage both during construction and as they continue to grow.

C2 – Ensuring a Site is Resistant to Moisture

This section focuses on drainage and moisture control, including damp-proof courses. The goal is to ensure proper drainage to remove excess water and prevent moisture from entering the building, especially through floor slabs and walls.

Drainage in Sub-Soil

This section applies to areas not prone to flooding. If the water table rises within 0.25m of the ground floor, proper drainage must be installed, using either gravity or another approved method.

If an existing drain is present during construction, one of these options must be followed:

• Relaying the drainage with sealed joints and adding access points
• Routing drainage around the building
• Redirecting drainage to another source

Proper site drainage is crucial where groundwater or surface water may threaten the building’s stability. For properties with basements or cellars, where foul water and rainwater drains together, there is a risk of sewage and excess water infiltrating. For solutions, refer to Approved Document H and CIRIA publications for blockage and backflow prevention.

Excavation during construction can disrupt groundwater flow and the soil’s ability to manage water. If contamination is present, drainage must prevent contaminants from reaching foundations or services.

Floors

This section outlines guidelines for common floor types, focusing on floors in contact with the ground. These floors should:

• Prevent moisture from rising into the surface floor
• Resist moisture damage
• Block harmful gases like Methane and Radon

Additionally, these floors must maintain structural and thermal integrity, preventing issues like interstitial condensation, surface condensation, and mould growth.

For a suspended timber ground floor, the following must be ensured:

• Ground is covered to prevent moisture and plant growth
• There is adequate ventilation between the floor and timbers
• Materials touching both the floor and timbers are separated by a damp proof course (DPC)

For more details, refer to Section 4.14 and Diagram 5 onwards of Approved Document C.

If a suspended concrete floor (precast concrete or beam and block) is used, it must prevent moisture from reaching the floor above and maintain structural integrity against moisture damage.

For exposed floors (e.g., above a garage or passageway), compliance with Clause 8.5 and Appendix D of the following British Standards is required:

• BS 5250:2002
• EN ISO 13788:2002
• BR 262

All floors must also resist condensation, mould growth, and maintain a thermal U-value under 0.7 W/m²K. Joints must conform to Accredited Construction Details or BRE IP17/01 guidance.

Walls

This section covers common wall issues related to contact with the ground and external elements:

• Moisture in external and internal walls exposed to the ground
• External walls affected by rain or moisture (e.g., solid walls, cavity walls, framed walls, cracks, cladding, and joints around doors and windows)
• Interstitial condensation within walls
• Surface condensation and mould risks on any wall type

To clarify as to what constitutes as a wall: A wall includes columns, parapets, piers, and chimneys when attached to the building.

In general, any wall should:

• Block water and moisture from entering the building
• Resist moisture damage
• Prevent rain, sea spray, and other precipitation from entering areas that could be damaged
• Ensure thermal and structural performance isn’t affected by interstitial condensation
• Stop surface condensation and mould growth

For structures used to store goods, parts 5.2(a) and (d) of Section 5 of Approved Document C may not apply, provided no health or safety risks are present during the handling of goods.

Roofs

This section covers roofs exposed to the elements, including precipitation (rain and moisture), interstitial condensation, and potential mould growth on internal surfaces.

Guidelines for roofs include:

• Block rain or moisture from entering the structure
• Prevent moisture damage and avoid transferring moisture to other building parts
• Maintain structural and thermal performance, unaffected by interstitial condensation

Use the above information as a general guide. For the latest and most accurate guidelines, always refer to the current version of Approved Document C. You can download it from the Planning Portal website via the link at the top of this page.