The joint pressures of population growth and the demands of Government policy mean that the UK’s brownfield sites are now a fundamental part in delivering today’s sustainable developments. However, our industrial past has left its mark with many of these brownfield land areas contaminated with hazardous waste or pollution. Phil Bull, Sales Director of Visqueen Building Products explores some of the recent innovations in membrane technology for protection against dangerous gases and chemicals, which enable architects and developers to safely build on these brownfield sites and meet all new stringent standards.
Brownfield development – the challenges
Brownfield is a term used for building on contaminated land, previously used for industrial uses which, by their nature, may have left several challenges in the ground such as the effects of hazardous waste or pollution. Since such contaminants cannot always be physically removed, barrier technology is an essential part of any redevelopment or building project to ensure these potential hazards are effectively contained. Failure to achieve this can lead to dire consequences.
Some of the worst UK tragedies where gas produced explosive or asphyxiating conditions include Loscoe in Derbyshire (1986)1, Abbeystead Lancashire (1984)2 and more recently in Gorebridge near Edinburgh (2012)3. The £8m Gorebridge housing development site was mothballed after occupants complained of dizziness and sickness which was directly attributed to ground gases not being effectively managed. Publicity surrounding these incidents heightened regulatory and public expectations for managing ground gas.
And as well as the serious safety implications, such incidents can also have a major long term negative effect on a developer’s reputation, made even worse in today’s social media dominated world where consumer complaints can be loudly heard and widely circulated.
Building on contaminated land – a guidance history
Although building regulations and codes of practice in general have evolved over the years to ensure safety during the development process, prior to 2007 most guidance took little account of risks associated with contaminated land and the best way to manage these. However the publication of CIRIA C655 and BS8485 changed this with the industry coming together for the first time to provide the necessary guidance and regulations surrounding the design, build and protective measures required.
In 2009 and 2012 CIRIA continued this with C682’s VOC handbook investigating and assessing risks from inhalation of VOCs at land affected by contaminations, whilst C716 provided guidance for remediating and mitigating these risks. Further developments resulted in 2014’s CIRIA C748 guidance on the use of membranes as VOC vapour barriers and the BS8485:2015 code of practice for the characterisation and remediation from ground gas in affected areas. BS8485 is the most recognised guidance documents when protecting new buildings from carbon dioxide and methane, setting a methane permeability of less than 40 ml/m2/d/atm for a gas membrane to ISO 15105-1 as well as expanded guidance on protection methods.
Compliance criteria for gas membranes
Understanding these standards has formed a key part of suppliers’ R&D programmes. Different hazards require different treatments and this had led to the introduction of a range of products specifically designed for particular applications – from radon gas protection through to VOC immersions and full waterproofing. And to help architects, developers and builders more easily identify the correct product for their specific requirements some manufacturers now offer a test checklist. This helps to ensure they are compliant with all the relevant regulations.
Where building projects take place on VOC contaminated land, manufacturers should always produce test data to support membrane suitability and not just modelled data. Such tests take into account the unique site conditions and highlight their specific requirements from methane permeability through to VOC vapours and immersions. The results can then to be used to enable designers to conduct the correct vapour intrusion modelling for the building development.
Selecting the appropriate membrane
As well as ensuring a membrane offers the right level of barrier protection, another essential consideration is the physical properties of the membrane itself. Many ground conditions are not ideal, with uneven contours, so flexibility of the material will be critical. Membranes which do not incorporate aluminium are less susceptible to puncture, corrosion, holing or cracking, which ensures that the barrier is maintained.
The level of support that a membrane manufacturer can offer in addition to the supply of product will also be important. For example, the availability of design specialists will allow the production of bespoke CAD drawings that help with complex detailing on a project; on-site technical teams can provide on-the-spot advice to ensure a smooth installation process.
Gas membranes – delivering protection for brownfield development
The demand to build more houses will ensure that the need to develop brownfield sites across the UK’s urban areas will continue. Already this has led to the introduction of much more stringent building regulations, and further legislation and even higher standards may be introduced in the future. New advanced barrier technology forms an integral part of gas protection solutions for architects, developers and builders. Careful assessment of what is available, supported by the experience and skills of membrane manufacturers, will be time well spent in ensuring the best and most appropriate solution for each new development’s specific requirements.