With a growing emphasis on sustainability (e.g. reducing embodied carbon) and safety (particularly in light of the Building Safety Act in England and Wales), this guidance from the Institution of Structural Engineers and Arup provides a 3-step method for assessing whether lower safety factors are acceptable when evaluating existing structures. The method will help engineers avoid unnecessary strengthening or demolition, while also enabling them to identify structures that are genuinely unsafe. Detailed guidance is provided on when safety factors can be reduced to account for greater certainty of structure and loads, and also how to assess the level of risk associated with structures that have ultimate-limit-state utilisations greater than 100%. The guidance also includes a full worked example, as well as the background to the method, and benchmarking comparisons.