Gas Membranes FAQ
WHAT IS A GAS BARRIER?
A relatively impermeable polymeric sheet or coating used as a barrier to prevent the migration of hazardous ground gases or vapours into new or existing structures.
Minimum protection measures differ as per the quantified risk to life:
- Basic Radon membranes are referred to by thickness of 300 micron (1200 gauge) virgin polyethylene with butyl taped sealed laps, refer to the guidance in BR211
- Methane / Carbon Dioxide membranes by the gas transmission rate and all points referred to in Table 7 of British Standards BS 8485: 2015+A1:2019
- VOC: Requirements as per CIRIA document C748 Membranes as VOC barriers
WHICH GAS BARRIER RELATES TO MY NEEDS?
If you have been advised that your building requires one of the following, we have created a comprehensive list of each product you will need in order to fit your gas barrier. These can vary from site to site so please contact customer service with any queries.
Radon Sump (Please contact customer services)
Methane / Carbon Dioxide: Low Risk (Amber 1)
Methane / Carbon Dioxide: High Risk (Amber 2)
VOC / Hydrocarbon
WHO NEEDS A GAS BARRIER?
All structures built on ground which may contain ground gases hazardous to human health as per the individual sites specific Geotechnical Engineers Detailed Quantitative Risk Assessment or otherwise advised by your Local Authority or Environment Agency in accordance with The Building Regulations 2010 Document C, Site Preparation and Resistance to Contaminates and Moisture.
NB: All soils emit levels of Radon Ground Gas, most UK Local Authorities now insist on a minimum protection layer of a basic Radon Barrier
Radon is referred to in UK national building regulation guidance. Guidance can be found in the following publications which relate to each specific UK region.
Department of Communities and Local Government (DCLG). The Building Regulations 2010 England. Approved Document C. Site preparation and resistance to contaminants and moisture. (2004 edition incorporating 2010 and 2013 amendments) London, NBS, 2013. Available www.gov.uk
Welsh Government. The Building Regulations 2010. (as amended in Wales). Approved Document C. Site preparation and resistance to contaminants and moisture. 2004 edition incorporating 2010 amendments. Available www.gov.wales
Scottish Building Standards Agency. The Building (Scotland) Regulations 2004, Domestic and Non-Domestic Technical Handbooks – Section 3. Available www.gov.scot
Northern Ireland Department of Finance and Personnel. The Building Regulations (Northern Ireland) 2012, (as amended).Technical Booklet C: 2012, Site preparation and resistance to contaminants and moisture. Available www.dfpni.gov.uk
In all four of these documents the reader is directed to BRE Report BR211 (2015) Radon: Protective measures for new buildings
Radon Protection as described in BR211 is in 2 levels:
- Basic: Basic radon protection consists of a well-installed damp-proof membrane, modified and extended to form a gas-tight radon-proof barrier between the ground and the building. Minimum thickness of 300 micron (1200 gauge) virgin polyethylene with butyl taped sealed laps.
- Full: Full radon protection comprises of a radon membrane that is fully sealed across the full foot print of the building and a radon sump or ventilated sub floor. Buildings with a large footprint or properties that have had extensions added, may require more than one sump system.
The Geotechnical Engineers Detailed Quantitative Risk Assessment may identify levels of hazardous ground gas exposure that poses a risk to human health for the gases Methane & Carbon Dioxide, in these instances the Structural Designer will use one of the following standards:
- National House Building Council - NHBC : Technical Extra Issue 20 2016. This will refer to the ‘Traffic Light’ system of Green / Amber 1 / Amber 2 / Red levels of protection. Specifically for new constructions covered by the NHBC.
- British Standards BS 8485: 2015+A1:2019 ‘ Code of practice for the design of protective measures for methane & carbon dioxide ground gases for new buildings’ . This code categorises risk into ‘Characteristics of Site’ (CS levels) which range from CS1 to CS6 (Table 2).
Ensure you know which design standard is being used as there are differences & your Local Authority may ask for proof of validation & verification prior to the building occupancy being allowed, if in doubt advice is available from HomeFix customer services.
Should the ground investigation Geotechnical engineers report (Detailed Quantitative Risk Assessment) show a risk is evident. The investigation is often an expensive process of driving bore holes into the ground & monitoring the gas emissions over a period of time, because of this many contractors choose to opt for Amber 2 / CS3 or above protection so they can save the cost of investigation. HomeFix is not responsible for offering site specific advice, always follow the engineers guidance.
Any Building Site with Accommodation which is detected to be at risk from Gas.
Radon : The guidance in BR211 applies to all new buildings, extensions, conversions and refurbishment for domestic or non-domestic use (unless subject to local exemptions contained within the specific regional Building Regulations.)
NB: All soils emit levels of Radon Ground Gas, most Local Authorities now insist on a minimum protection layer of a basic Radon Barrier (300 micron virgin polyethylene as opposed to 100/200 micron recycled polyethylene damp proof membrane).
Methane & Carbon Dioxide: Any person or building may be at risk of exposure to health threatening hazardous ground gases. This is identified in British Standards BS 8485:2015+A1:2019 ‘Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings’ under Table 3, categories range from Type A (private dwelling) to Type D (commercial warehouse / hanger). Type A is the most stringent.
Be aware that Type C & D structures, though large and well ventilated, may include areas which come under stricter types of categories such as offices, laboratories, toilets etc and these may require greater complexity in protection.
VOC & Hydrocarbons: Always seek professional advice prior to construction: Refer to CIRIA reports; C716 Remediating and mitigating risks from volatile organic compound (VOC) vapours from land affected by contamination
C748 Membranes as VOC barriers and C735 Good practise on the testing and verification of protection systems for buildings against hazardous ground gases.
WHY DO I NEED A GAS BARRIER?
Simple answer. ‘To save your life or the lives of the occupants who will live in the building you're constructing’.
Hazardous ground gases are normally aligned under 4 main categories (Radon, Methane, Carbon Dioxide & Volatile Organic Compounds / Hydrocarbons) though the full range of variants is extensive and possibly infinite.
Each category poses a proven risk to life:
- Radon: Carcinogenic, Public Health England conservatively estimate 1100 deaths per year of Lung Cancer resultant from exposure to Radon nuclides. The action level endorsed by Public Health England (PHE) is 200 becquerels per cubic metre (Bq-m³), the target level is 100 Bq-m³. PHE recommends that radon levels are to be reduced to the target level or lower.
- Methane: Asphyxiation becomes a risk when there are high concentrations of methane. As methane displaces the oxygen in a confined space immediate loss of consciousness can occur and inevitably death. Methane explodes at volumetric concentration in the air of 4.9 to 15.4%.
- Carbon Dioxide: Depending on the CO2 concentration inhaled and exposure duration, toxicological symptoms in humans range from headaches (in the order of 3% for 1 hour), increased respiratory and heart rate, dizziness, muscle twitching, confusion, unconsciousness, coma and death (in the order of >15% for 1 minute). Refer HSE Document ‘Assessment of the major hazard potential of carbon dioxide (CO2 ) A paper by: Dr Peter Harper, Health and Safety Executive (HSE) Advisers: Ms Jill Wilday (HSL) and Mr Mike Bilio (OSD)’
- VOC / Hydrocarbons: Volatile Organic Compounds are organic chemicals which evaporate easily at room temperature, these include but are not restricted to hydrocarbons. Hydrocarbons are organic compounds of hydrogen and carbon. At normal temperatures both exist in the liquid and vapour phases. VOC’s & Hydrocarbons may be extremely hazardous to health and lethal, exposure to hydrogen cyanide (AC) can be rapidly fatal (less than 30 minutes exposure). It has whole-body (systemic) effects, particularly affecting those organ systems most sensitive to low oxygen levels: the central nervous system (brain), the cardiovascular system (heart and blood vessels), and the pulmonary system (lungs). VOC barriers must be immediately effective upon application.
WHAT DO THE TERMS ON MY BUILDING REGULATIONS MEAN?
NHBC – Amber 1 / Amber 2Differing levels of ground gas barrier protection & levels of validation and verification, only to be used for National House Building Council designs & projects
BS 8485:2015+A1:2019: Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings, UK accepted design standard for protection against Methane and Carbon DioxideCIRIA 735
A document by the Construction Industry Research and Information Association: CIRIA 735 Good practice on the testing and verification of protection systems for buildings against hazardous ground gases – Explains in detail the requirements for independent Verification & Reporting of the application of the ground gas protection system. Highly important, it is often mandatory for building occupancy.
BRE Report BR211 (2015) Radon: Protective measures for new buildings
Carcinogenic radioactive ground gas, emitted from all soils, that kills 1100 per year in England & Wales. Heavy than air, moves through atmospheric changes and attachment to water molecules.
Deadly ground gas. Simplest form of hydrocarbon, both flammable & inflammable. Lighter than air.
CO2 / Carbon Dioxide
Deadly ground gas, asphyxiant & irritant. Lighter than air.
Highly toxic, often explosive, usually lethal ground gas & vapour (a vapour may sit on your skin).
Highly toxic, often explosive, usually lethal ground gas & vapour (a vapour may sit on your skin)
FYI: Vapour is a mixture of two or more different phases at room temperature, these phases are liquid and gaseous phase.
CAN I BUY AND FIT A GAS BARRIER MYSELF?
In simple terms, yes, certainly as a basic Radon Barrier. As all BS / NHBC / BRE / CIRIA are design standards & guidance, you can simply choose not to use them. However, should you not opt for a team led by a qualified construction professional (NVQ level 2 Gas Membrane Installation) the levels of validation & verification will be increased. Refer below.
Radon barrier: yes but you must be able to provide evidence of correct product purchase and that it has been installed correctly as per the manufacturers instructions to the local authority.
Methane & CO2 Barriers: yes but you must be able to provide evidence that the protection system (membrane, tapes, venting, protection, etc) has been Independently Validated. Validation is the process of assessing that all the separate components (chosen system, design etc) is correct for the specific building application.
- For BS 8485:2015+A1:2019 any project of CS2 or above must be independently verified in accordance with CIRIA 735
- For NHBC Amber 1 sites you must be able to provide clear evidence of application verification & monitoring to the Local Authority that the application team has been trained and the system has been installed correctly under the minimum guidance of NHBC Document
- For NHBC Amber 2 sites you must be independently verified in accordance with CIRIA 735
VOC & Hydrocarbon Barriers: Always seek professional advice prior to construction: Refer to CIRIA reports; C716 Remediating and mitigating risks from volatile organic compound (VOC) vapours from land affected by contamination, C748 Membranes as VOC barriers and C735 Good practise on the testing and verification of protection systems for buildings against hazardous ground gases.
To learn more about the Validation & Verification of systems designed to protect against the ingress of hazardous ground gases into new constructions HomeFix recommend that the purchaser / installer discusses their requirements with an independent validation & verification organization for advice.
All advice and recommendations given by any Validation & Verification company are not representative of any HomeFix instructions and are direct comments / correspondence between the Client & the Validation & Verification company.
HomeFix advises contacting GeoShield Ltd, Verification Programs for Ground Gas Protection Systems, on 0113 320 8639 or via firstname.lastname@example.org. GeoShield operate throughout the UK & Europe. (NB: the customer is at liberty to source advice from any independent validation & verification company of their choice).