The BS 8485 is a very important set of regulations when it comes to ground gas protection. It is the guidebook that tells us how we decide when we need a ground gas protection system and what kind of solution we need. In this blog, we’ll explain the key points about this document and why it is necessary to stick to it.

What Does bs 8485 cover?

BS 8485 is the British Standard for protecting new buildings from CO2 and methane ingress. It’s the code of practice for the design of protective measures for methane and carbon dioxide ground gasses for new buildings. It does not apply to refurbishments, only new buildings.

What is the purpose of bs 8485?

BS 8485 sets out the British Standard for determining the risk of CO2 and methane affecting new buildings by calculating the Gas Screening Value (GSV). It shows us how to take information from geotechnical survey report, calculate the CS rating (this is the “Characteristic Situation” and is allocated a score from one to six) of the GSV and the building type, A, B, C or D, for example, if it’s residential, commercial offices, swimming pool etc. We can then use this CS rating as points score so we know how to design our ground gas protection system for that particular building and ensure that it is adequate for those specific site conditions.

This is important as every site is different. Construction happens all over the country and ground conditions can vary dramatically. In some areas there is lots of mining, others, lots of landfill. Some sites could even have a high amount of naturally decaying peat, producing CO2. It should be assumed that every site is different, and BS 8485 provides us with a formula to standardise how we protect our buildings from potentially harmful ground gasses.

On What Projects is BS 8485 applicable?

The answer here is simple - all new building sites. Fortunately, there may be cases where the CS score is 0, so BS 8485 would tell us that our ground gas protection would need to meet these requirements. In other words, no system would be required. On other sites where there are ground gasses present, we would need to meet these with appropriate protection systems.

The requirement for a Ground Gas Protection System is highlighted by Geotechnical Specialists. If protection is required, the installation of the ground gas protection system becomes a planning condition which needs discharging to be a permitted development.

What are the legal dangers of not adhering to bs 8485?

Before we answer this, let’s take a look at the process of how a site is assessed. A geotechnical survey is first carried out and a CS rating calculated, if it is determined that a ground gas protection system is required then it will be passed on to the local planning authority. They will make it a requirement for the CS rating to be met. If these requirements are not met or independently verified, the planning conditions will not be discharged, and the building will not be a permitted development. The local planning authority can order this to be rectified or stop development. If it is found out that requirements have not been met after the development is built, the planning conditions may not be discharged, and the development would not be permitted. There are recent examples of this occurring in new residential homes. The bank valuation surveyors then valued the properties at £0 as they were not permitted developments.

What are the physical dangers of not adhering to bs 8485?

When BS 8485 regulations are not met, the risk of ingress from harmful ground gasses increases massively. The damaging effects these can have on human health cannot be understated. Exposure to harmful gasses can cause early symptoms of asphyxiation as oxygen is displaced, such as dizziness, headaches, nausea, feeling sick, oversleeping or feeling over tired. Methane levels between 7-14% can actually be explosive and has been known to cause explosions when just the right concoction is created.

Who is responsible for making sure standards are adhered to?

As with all things in construction, it is a team collaboration to make sure a ground gas protection system is installed correctly. The Geotechnical Specialists would highlight the ground gases detected in the ground. The Local Planning Authority will create a planning condition stating recommendations within the Geotechnical Survey Report must be met. The Design Team must design a suitable Ground Gas Protection System. The Independent Verifier will carry out verification in accordance with CIRIA 735, including Pre-Verification Plan, Testing, and Verification Reports. The Installation Team will carry out the installation and ultimately take responsibility for that installation. The Independent Verifier then provides evidence to the Local Planning Authority so the Planning Condition can be discharged.

How does PUDLO work within the standards?

We offer a design service that complies with BS 8485. By Sending us your Geotechnical Survey Report, design details for the proposed development and providing time to discuss the project, we will be able to provide the Ground Gas Protection Design in accordance with BS8485:2019.

We would specify PUDLO Products that are all tested in accordance with BS8485:2019 and BBA Certified. Depending on the site specific risks, we can either recommend NVQ Level 2 Ground Gas Membrane Installers or carry out Toolbox Talks on site. Depending on site specifics, we may also provide a warranty for up to 10+ years.

This has been a quick look at the key elements of BS 8485. We hope that this has answered some questions you may have had around the standards. If you would like to know more about how PUDLO can provide ground gas protection with your projects, then please get in touch with us.

Phone: 01954 780687, Email:

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