Great Britain has a temperate climate, but like other countries, its weather patterns have already been profoundly affected by climate change, and the changes are very likely to continue for decades. It also has an older building stock than most other countries, which may mean it is more difficult to adapt the built environment to reduce vulnerability to climate hazards. However, Great Britain has excellent mapping and buildings data. The built environment is better described than most other countries, and the authors’ work on the National Buildings Database for Great Britain, which draws together the most reliable sources of data covering non-domestic buildings in England, Scotland and Wales, provides an unparalleled opportunity to evaluate how many people will be affected by climate hazards. There has been considerable research effort assessing how housing will be affected by climate change, but so far much less systematic assessment of impacts on non-domestic buildings. Here, the authors examine three aspects of climate hazard affecting people in non-domestic buildings in Great Britain: (1) Overheating—How many and what types of non-domestic buildings are vulnerable to overheating risks in a heat wave? What total floor area is affected, and how many people typically occupy these buildings? (2) Flooding—How many and what types of non-domestic buildings are threatened by flooding now and in 2080? How much floorspace is threatened, and how many people typically occupy these buildings? (3) Safe space—How much air-conditioned ‘safe space’ is available where people vulnerable to overheating risks could retreat to in an emergency overheating event (e.g., schools or hospitals)? How many people could be accommodated, and what fraction of the total GB working population does this represent? We propose five new metrics to assess two of the immediate hazards posed by climate change (overheating and flooding) and to begin to assess to what extent Great Britain could find temporary accommodation for people displaced by these hazards.