BS 8485:2015 Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings has been amended and replaced by: BS 8485:2015+A1:2019. 

It describes how to characterize sites and prevent the entry of toxic, asphyxiating or explosive ground gases.

This 2019 amendment changes and clarifies:

• The minimum gas protection points required for Buildings Type B, C and D on High and Very High gas hazard sites. scoring methods
• The assignment of gas protection points for the structural barrier for basements.
• The criteria for membranes that can be assigned 2 gas protection points when used as a gas resistant membrane.
• The membrane thickness test method applicable to the guidance in the code of practice.

BS 8485:2015 is now withdrawn. Futher information is available here.