This report gives guidance for reducing the concentration of radon in new buildings, extensions, conversions, and refurbishment, to reduce the risk to occupants of exposure to radon. It provides practical details on methods of protecting new buildings, extensions, conversions and refurbishment, both domestic and non-domestic. This guide is intended for use in England, Wales, Scotland and Northern Ireland, and supports building regulations for England, Wales and Northern Ireland, and building standards for Scotland. This guide was originally introduced in 1991 and amended in 1992, 1999 and 2007. This 2015 edition replaces the guidance published in 2007. This combined guide replaces three earlier guidance documents:- BRE Report BR 211, Radon: guidance on protective measures for new buildings, originally introduced in 1991 and amended in 1992, 1999 and 2007 covering England and Wales. - BRE Report BR 376, Radon: guidance on protective measures for new dwellings in Scotland, introduced in 1999. - BRE Report BR 413, Radon: guidance on protective measures for new dwellings in Northern Ireland, introduced in 2001.