Harmful, naturally occurring below-ground gases and vapours pose a growing challenge for the construction industry.

Radon, carbon dioxide, methane and VOCs (Volatile Organic Compounds such as hydrocarbons) are a risk to health and new buildings have to use appropriate materials to keep these gases out of the structure.

Download VOC and Gas Barriers Brochure

The below illustration, shows the key routes of contamination:

Possible ingress points

  • Cracks in solid concrete ground slabs, caused by shrinkage and curing
  • Construction joints where ground slab isn’t sealed at the wall-foundation joining
  • Gaps in suspended block and beam floors or timber floors
  • Gaps around or within service pipes and ducts
  • Cracks in walls below ground level
  • Cavity walls

Ground Gas Standards

There are many different standards and guidance documents that detail how to understand the risk of ground contamination, and design solutions to mitigate these risks. The different documents relate to different ground contamination. Below are some of the key documents to be aware of and refer to:

Methane (CH4) and Carbon Dioxide (CO2)

BS 8485:2015+A1:2019 – Codes of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings.

  • Ground gases typically found near landfill sites, but can occur from other sources
  • Encourages the use of qualified installers
  • Validation to Ciria C735 is a requirement
  • Additional influences on the system should be considered, such as the hydrostatic conditions, and the likelihood of the source contaminant being in direct contact with the protective measures proposed

Radon (Rn)

BRE 211:2015 – Guidance on protective measures for new buildings. (RADON)

  • Naturally occurring ground gas. Larger concentrations in the South-West of UK
  • Minimum recommendation is a membrane of 300 micrometre (1200 gauge) polyethylene sheet or equivalent
  • It must be installed with considerable care and protected once installed
  • Taped laps are required

VOCs (Hydrocarbon vapours / Hydrocarbon liquids)

CIRIA C748:2014 – Guidance on the use of plastic membranes as VOC vapour barriers
CIRIA C682:2009 – VOC Handbook

  • Risk based approach
  • No quantifiable limits on material performance
  • Testing to ISO 15105-2 and EN 14414/EN 14415
  • 9 main VOC types are tested for
  • Welded laps are required as most tapes are made from bitumen/butyl and are affected by VOCs


CIRIA C735:2014 – Good practice on testing and verification of protection systems to buildings from hazardous gases

  • Good practice on testing and verification of protection systems to buildings from hazardous gases
  • Check design and detailing is in accordance with site requirements
  • Checks the competency of the installer (NVQ LEVEL 2 minimum)
  • Test integrity of the membrane/barrier system
  • Visual inspection
  • Written report on inspection/testing and sign-off

BS8102:2009 – Code of practice for protection of below ground structures against water from the ground

Sika Solutions

Sika has introduced a range of products that will address the growing need for protection from below ground gases:

  • 1
  • 2
  • 3

A – Ground-level

Ground-level damp-proofing and gas protection as an extension of our below ground SikaProof®-A and -P waterproofing systems.

1 – Sikaplan®-1650 DPM Gas Barrier
2 – SikaProof®-A or -P
3 – SikaProof®-A

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  • 5
  • 6

B – Ground-level and belowground

Ground-level and belowground protection where VOCs are also present.

4 – Sikaplan®-1651 Loose VOC Gas Barrier
5 – Sikaplan®-1652 Bonded VOC Gas Barrier or Sikaplan®-1653 Adhered VOC Gas Barrier
6 – Sikaplan®-1652 Bonded VOC Gas Barrier