Membrane Installation Case Study – Stourport Road, Kidderminster
Redevelopment of the 74 acre British Sugar Site in Stourport Road, Kidderminster including 160 house plots requiring ground gas protection.
Guidance from Ciria report C665 “Assessing Risks Posed by Hazardous Ground Gasses to buildings” uses gas concentrations and flow rates to calculate the Gas Screening Value (GSV). The highest recorded values for methane and carbon dioxide are then used to calculate the GSV for the worst case scenario and the site given a characterisation. In this case the site fell into the category of CS3 (Moderate Risk) for which specialised ground gas protection measures are required. With the additional guidance provided by BS8485 2015 the “Code of Practise for the design of protected measures for methane and Carbon dioxide ground gasses for new buildings” the gas protection measures need to provide a point score of 4.5 points which can be achieved by installing a properly installed and validated gas barrier and a system of ‘Very good’ sub floor ventilation.
The normal rational of a beam and block floor with vented void below and a gas barrier and insulation above was turned upside down by the use of the novel insulslab system which incorporates an interlocking series of polystyrene pods to form a ridged waffle type foundation/slab over which is poured a steel fibre reinforced concrete. This method of construction required the gas barrier to be placed below the slab and below the barrier a vented void to be formed from a 25mm void former.