- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 05 Aug 2018
Methane and other site gases from the ground
Approved document C, Site preparation and resistance to contaminants and moisture, suggests that ‘methane and other gases’ includes hazardous soil gases (other than radon, which is dealt with separately), which originate from waste deposited in landfill or are generated naturally.
They may include gases such as methane, carbon dioxide, volatile organic compounds (VOCs) and nitrogen which can migrate through the subsoil and through cracks and fissures into buildings, where if they build up to hazardous levels, cause harm to health or compromise safety:
- Methane is an explosive and asphyxiating gas.
- Carbon dioxide is toxic.
- VOCs are flammable and toxic and can have an unpleasant odour.
They may be apparent as:
- Landfill gas, produced by the action of micro-organisms on biodegradable waste materials, including; methane, carbon dioxide and small quantities of VOCs.
- Elevated levels of carbon dioxide and nitrogen, occurring naturally in coal-mining areas
- Methane and carbon dioxide occurring in organic rich soils and sediments such as peat and river silts.
- VOCs occurring as a result of petrol, oil or solvent spillages.
The assessment of the risk from ground gases should adopt a tiered approach. A preliminary risk assessment should be undertaken, and depending on the outcome, either a generic quantitative risk assessment (GQRA) or detailed quantitative risk assessment (DQRA), or both, may be necessary.
Where risks are unacceptable then these need to be managed through appropriate building remedial measures or site-wide gas control measures, such as the removal of the gas generating material or 'covering' (placing one or more layers of materials over the site) together and the use of gas extraction systems.
Control measures for dwellings may include gas resistant barriers above an extraction or ventilation layer from which gases can be passively dispersed and vented to the atmosphere.
Control measures for non-domestic buildings, which may have a larger footprint, may require mechanical dispersal and ventilation systems, monitoring and alarms. These systems will require ongoing maintenance and calibration.
 Related articles on Designing Buildings Wiki
- Brownfield land.
- Building on fill.
- Contaminated land.
- Cover systems for land regeneration - thickness of cover systems for contaminated land (BR465).
- Deleterious materials.
- Designing to reduce the chemical, biological and radiological vulnerability of new buildings (IP 7/15).
- Ground conditions.
- Landfill tax.
- Pre construction information.
- Radon: Guidance on protective measures for new buildings BR 211.
- Radon protection for new domestic extensions and conservatories with solid concrete ground floors (GG 73 revised).
- Radon protection for new large buildings GG 75.
- Radon protection for new dwellings GG 74.
- Site appraisal.
- Site information.
- Soil survey.
- Solid and liquid contaminants risk assessments.
Featured articles and news
How to get results with building life cycle assessment.
Government publishes a prospectus inviting proposals for new 'garden communities'.
The Morandi motorway bridge in Genoa collapses during rainstorm while undergoing maintenance works.
'Developed design' is a phrase coined by the RIBA for their 2013 Plan of Work. But what does it actually mean?
New green paper published aiming to rebalance the relationship between landlords and residents and tackle stigma.
RIBA calls for a comprehensive ban on combustible materials.
Lump sum contracts can be referred to as ‘fixed price’ contracts, although strictly this is not correct. Find out more here.
Ramboll offer guidance to civil engineers on how to make projects 'off-site ready'.
Government announces its Rough Sleeping Strategy, with further funding for social housing.
An overlooked architect who deserves to be celebrated for his wide range of buildings.
The Home Quality Mark ONE technical manuals for new homes are now available.