Southampton Ground Gas Protection
Inspection Experts

UK is experiencing an increase in harmful, naturally occurring sub-ground gases and vapours. It is important that the dangers and presence of ground gases be assessed in order to protect the structure.

There are two possible sources of gas that could be present on a site: they can be natural or they can be a result from its history.

Natural gases include methane and carbon dioxide as well as nitrogen and radon. These gases are often found in soils at higher levels than the normal atmospheric gases.

Sites used in the past for landfill, heavy industrial, or where petrol or oil may have leaked can also emit hazardous gases like methane or carbon dioxide.

Each of the gases and vapours mentioned above have different properties. Some are asphyxiating, flammable and potentially explosive. Others can be toxic and, over many decades, can cause cancer. Some may also chemically interact with the concrete and plastic building materials, affecting the structural integrity of the building. They can be found in buildings and other structures above and below ground.

The different types of gases are;


Radon, carbon dioxide methane, methane, and VOCs (Volatile Organic Chemical Compounds such hydrocarbons) pose a threat to human health. New constructions must contain the right materials to prevent these gases from entering the structure. They must also be installed according to the recommended guidelines.

According to CIRIA C735, a separate ‘Gas safety verification plan’ (or ‘Gas protection verification document’) is required. A robust design and construction process should then be followed to install the gas protection measures and the requirements of ‘verification plan’ implemented. After the construction has been verified, it is time to prepare handover documentation. This document should outline any additional measures that may be required, such as those necessary for preventing damage or during operation and maintenance.

It is recommended that specialist advice is obtained in the assessment of the ground gas data and at the risk assessment phase. Here are some key documents that you should be aware of.

BS8485+A1 2019 offers recommendations on ground-gas site characterisation and the selections of solutions to design integral gas protective mechanisms for new buildings. This is done in order to prevent methane and carbon dioxide from entering and maintain a safe interior environment. It provides a way to demonstrate that potential or actual carbon dioxide and methane risks have been mitigated.

To ensure the installation of your gas protection systems meets CIRIA 735 & BS8485 please call our Southampton team

How does ground gas happen?

Both brownfield and greenfield sites could be exposed to harmful ground gases. Some gases are found naturally in the ground and others are caused by human activities such as mining, dumping, landfilling, and mining. These and other activities have caused pollution and created conditions where harmful gasses build up in the ground. The potential for high concentrations in harmful ground gases to pose health risks to people who live near them or are working on their behalf.

Why is ground gas becoming a problem?

Ground gases were not considered a danger to buildings or users in the past. Due to increasing demand for homes, brownfield sites have seen an increase in development. This is because it is more difficult to find new land to develop. Brownfield sites can have pollutants that affect the soil and ground.

The Environment Agency’s increased awareness of potential risks has led to new legislation being adopted by local authorities in all parts of the country.

It is important that you note that possible risk factors cannot be determined without a detailed ground gas investigation by a qualified ground gas surveyor.

Assessment of ground gas risks

At the desk stage, ground gas and vapour risks are assessed. Ground investigation or assessment is then done. If ground gas hazards are discovered, measurement with monitoring wells in boreholes will usually be part of the investigations. Existing buildings can be monitored using static measurement methods and diffusion tubes. The nature of the risk can affect the length of monitoring programs. They may last for days or even months.

After the investigation is completed, it will be possible to interpret the measurement data and determine whether there is a danger from ground gases.

Protection against below ground gases

Ground gas protection requires a high level of expertise. The GeoShields Ground Gas experts have the knowledge, experience, and skill to do it.

Ground gas protection is often achieved by ventilation and ground membranes in construction. This provides primary and secondary protection against the ingress of gases. If you are already a homeowner living in a property then foundation based ground gas protection will most likely be impractical. Therefore ventilation is the key. Natural ventilation can be used for suspended floors or improved underfloor ventilation. Mechanical ventilation systems can also be used to ventilate the property. This allows harmful ground gases to be controlled and vented safely. In all cases validation of the construction and the installation techniques is important.

There are some situations where gases and vapours may pose risks because they are a byproduct of soil or groundwater contamination. This can be mitigated by remediating the source of contamination.

What could be the effect of doing nothing?

The effect of not reacting to potential ground gas risks depends on which type of ground gas was discovered. Some may affect your health while others can damage the integrity of the building. Radon can cause lung cancer. Carbon Dioxide can cause asphyxiation and can be deadly. Methane, Volatile organic compounds, and Methane can all be explosive/flammable. Low levels of Methane (5%) can make it flammable.

You may find that the property is too risky for mortgage lenders.

What is Ground Gas Membrane?

Due to the hazardous nature of ground gasses, buildings should be protected to ensure safety and integrity. Protection is usually in the for of a ground gas membrane.

Ground gas protection membranes are typically made from polymers, but can also be made with other materials like aluminium. This allows them to be light and flexible while still being formable. They prevent gas from flowing into the building from the ground.

To ensure the installation of your gas protection systems meets CIRIA 735 & BS8485 please call our Southampton team