Ground Gas Protection – Lessons for Developers
The Key challenges – The importance of getting it right
As the government, local authorities and developers continue to address the UK housing supply shortage, key issues around
the suitability of land, as well as the safety, health and well-being of the occupants, must be a priority. Identifying sufficient
suitable land almost certainly will require the safe development of housing on brownfield sites. Lessons from the past
provide a vital warning for developers on the importance of getting it right the first time.
Two recent examples can help highlight the crucial role of ground gas protection and how not getting it right the
consequences can huge. The first example relates to a housing development built in 2009 at Gorebridge, Midlothian in
Scotland. However, the ground gas problem didn’t emerge until four years later in 2013. This resulted in dozens of families
being evacuated from Newbyres Crescent after potentially deadly carbon dioxide (CO2) leaked into their homes from old
mine workings in proximity to the site. As a consequence, in 2016 all 64 houses on the estate were torn down. The legal
battle is still ongoing to litigate those who were responsible.
A second example covers a development built in 2014. The estate adjoins a former landfill site, which had not been used
for 40 years but the risk remained of methane gas being released from underground. The developer was required to fit a
layer of membrane to prevent gas from escaping into the houses, but homeowners have no evidence that this was carried
out. It was subsequently clear that the development had not been completed in line with planning permission requirements
and final building compliance certificates had not been issued. One homeowner who had bought a home for £130,000 in
2014, later attempted to get the home revalued as part of a remortgaging process. When the documents were returned, an
estimated value of £0 was returned as a result of the problem.
Guidance and legislation – What you need to know
Key guidance for methane and CO2
ground gas protection is available for developers in the form of BS8485:2015 + A1
BS8485:2015 + A1 2019 is the ‘Code of practice for the design of protective measures for methane and carbon dioxide
ground gases for new buildings.’
Toxic, asphyxiating and flammable and potentially explosive ground gases can enter buildings and other structures on and
below the ground. They variously pose potential risks to occupants and users, and the structures themselves.
The British Standard is to be used by designers of gas protection measures and by regulators involved in the assessment
of design solutions. It recognizes that there are several factors which affect the sensitivity of a development concerning the
effects of ground gas and which need to be considered. It also describes a range of design solutions available for different
situations. It is recommended that specialist advice is obtained in the assessment of the ground gas data and at the risk
BS8485:2015 + A1 2019 provides recommendations on ground gas site characterisation and the choice of solutions for
the design of integral gas protective measures for new buildings to prevent the entry of carbon dioxide and methane and
provide a safe internal environment. It offers a process that can be used to demonstrate that risks posed by the potential or
actual presence of carbon dioxide and methane have been addressed.
Protection in practice – Lime Kilns, East Calder
An example of good practice in ground gas protection specification is highlighted at a new development of two residential
properties at Lime Kilns, East Calder in Scotland.
Prior to construction and in line with the guidance and legislation for brownfield site developments, an investigation of the
site revealed the presence of historic VOCs, Methane and CO2. In full compliance with CIRIA C735 and the guidelines laid
out in the British Standard 8485:2015 (+ A1 2019) and CIRIA C748, the chosen geomembrane, Protech VOC Flex from
the A. Proctor Group was installed by the specialist gas membrane contractor Structureseal Services. As laid out in CIRIA
C735 the VOC geomembrane was thermal heat welded and all joints air lance tested in accordance with ASTM D4437-08
2013 in conjunction with the third-party validation engineer. The thermal heat welded joints were carried out by approved
NVQ Level 2 gas membrane installers, including the installation of the A Proctor Group’s Provoid 25 cuspated geocomposite
subfloor venting blanket to form a passive dispersal layer in conjunction with Provoid ground mounted gully vents to the
perimeter of the houses. This combined achieved a “very good performance” passive venting installation fully compliant with
BS8485:2015 (+A1 2019) Table 6.
Martin Taylor, Commercial Director of Structureseal Services commented, “we have successfully used Protech VOC Flex on
several VOC vapour protection projects. It offers high-performance protection in compliance with CIRIA C748, is extremely
robust and has many benefits which make it easy to install on site. One of these being that when the geomembrane is
folded the product has “memory”, which enhances the speed, finished appearance and quality of the overall installation.
Protech VOC Flex is a 6-layer flexible proprietary reinforced VOC gas barrier suitable for use on brownfield sites that
require protection from dangerous contaminants.”
The manufacturer’s design and specification advice allowed the project at East Calder on behalf of Concept Completed, to
achieve a fully compliant design for ground gas protection measures. Developers, specifiers and contractors should consult
closely with manufacturers to access technical expertise include CAD detailing and project-specific recommendations
utilising the latest guidance and ensure compliance with current legislation and standards including BS8485:2015 (+ A1 2019)
and CIRIA C748. This approach, complete with a full range of site investigation reports and gas monitoring results will ensure
full compliance and the correct product selection.