Defining the scope of gas protection

Low-rise housing Suspended floor slab Ventilated underfloor void 

High-rise housing Housing with ground bearing slabs/rafts Commercial Schools Warehousing Industrial Offices 

2 Low-rise housing with gardens (Situation B in CIRIA C659/665) 

Once tire traffic light classification has been determined the appropriate level of protection can be defined using the NHBC guidance or CIRIA C659/665 (Boyle and Witiierington, 2007 Wilson et ah, 2006, 2007). The requirements are summarised below  

I Green No protection required (over and above the underfloor ventilated void that is assumed in the use of this approach). 

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The scope of a gas protection system is based on the results of the risk assessment. A combination of measures is usually used to minimise the risks associated with ground gas. This is so that if one element of the protection fails the others will continue to protect the development. Once the scope has been defined, detailed design of individual elements such as the venting or membranes can be completed. The latest QRIA guidance has two methods of defining the scope of gas protection one that is for low-rise housing and a ventilated underfloor void (minimum 150 mm high) the other is for any other type of development. 

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