NHBC has said that despite lots of guidance for assessing ground gas risk, it is still frequently seeing inadequate assessment, design and installation of protection measures on new homes.
“There are an uncomfortably high number of houses that need systems to be retro fitted, which is compromising design and delaying house sales,” said NHBC principal geoenvironmental engineer Gavin Allsopp at the AGS Ground Risk: Why take the chance conference yesterday in London.
According to Allsopp, many project do undertake the correct amount of gas monitoring but are failing to look at the wider picture and consider what is being built and what the risk is to that structure.
“Just because there is an exceedance in ground gas, it doesn’t always mean there is a risk,” he said.
“The key is getting the conceptual site model correct in order to identify a ground gas source and the ability for a pathway to create a risk. Engineers need to consider if the monitoring is representative of the long term conditions at the site and confirm that there is a valid pollutant link.”
Allsopp said that a number of sites without risk are having gas protection installed where the gas monitoring has been done but it has not been linked back to the conceptual model and there is no real risk. However, it is the sites where the risks have not been properly considered until after construction has started that concern him and he urged the industry to improve standards.