Retrofitting hazardous ground gas protection measures in existing or refurbished buildings

A substantial body of guidance relating to hazardous ground gas has been published over the last 30 years or so, the large majority of which relates to the assessment, design, and construction of gas protection measures to new buildings. Although there is some guidance on the retrofitting of gas protection measures to existing buildings (much of it related to radon) the absence of specific advice regarding retrofitting has resulted in instances of the inappropriate application of the guidance for new buildings. This publication provides good practice guidance on the retrofitting of hazardous ground gas protection measures in existing buildings where these measures were absent, inadequate or faulty, as well as buildings subject to extension (lateral or basement) or refurbishment. It is relevant to the risk assessor, designer, installer, verifier, and regulator involved in such a project. Throughout this guide hazardous ground gas is used as an overarching term to refer to permanent gases, methane, carbon dioxide and carbon monoxide, and to volatile organic compounds (VOCs), and radon.