Gas generated by the breakdown of organic material in nearby landfill sites or buried waste; or from naturally occuring gases from peat, alluvium, Coal Measures strata or other sources has the ability to seep into buildings and create either an explosive, toxic or asphyxiation risk. These gasses include carbon dioxide, methane among others.
BS8485:2015 is the British Standard that covers the design and installation of gas protection membranes within new buildings, and this guidance states that membranes must be "verified in accordance with CIRIA C735".
We have recently finished the verification of a CS2 gas protection measures to BS8485 at a residential housing protection measures at a development between Nuneaton and Coventry, Warwickshire; near Birmingham. The existence of possible ground gases was indicated by a Phase 1 desk study, which indicated underlying Coal Measures strata and nearby thick made ground. A phase 2 site investigation consisted of (among other things) the installation of standpipes and gas monitoring visits that confirmed elevated carbon dioxide levels. In accordance with BS8485:2015, the site was classified as Characteristic Situation 2 (CS2) and a gas protection membrane and underfloor ventilated void were designed to mitigate the risk.
A verification plan was written and submitted for regulatory approval; taking into account the measures designed, the gas regime, the installers experience and the construction timetable. When construction occurred and the protection measures were installed inspections were scheduled and, upon completion, a final verification report was produced for final regulatory approval.
If you need ground gas verification to C735 or have a contaminated land planning condition on your site drop us a line on this email or phone Murray on 07858 367 125.