Homes contribute 22% of UK carbon emissions, 45% of which are primarily for space heating energy. Delivery of highly insulated homes, newbuild and retroﬁt, is needed to help meet the UK’s 2050 net zero carbon target. Similar policies are being adopted across the developed world to limit rising carbon emissions. Unfortunately, most new and retroﬁtted buildings use much more energy than predicted by computer models at design stage, up to 250% more, the so-called ‘energy performance gap’. Although emerging evidence suggests that buildings built to the low-energy Passivhaus standard do not demonstrate such a gap, data are often from small-scale forensic investigations. Here, we present the ﬁrst large-scale systematic evaluation of this standard in occupied buildings using multi-year data from 97 UK Passivhaus dwellings spread across 13 sites. As frequency and type of data collection varies between sites, we adopt a pessimistic approach to the analysis by systematically over-estimating space heating demand in the presence of uncertain data. Results pooled across multiple years, show that mean observed space heating demand is 10.8 kWhm2a-1 (SD 9.1) with no statistically signiﬁcant difference against predicted demand of 11.7 kWhm2a-1 (p = 0.43, d = 0.1). These results provide powerful evidence in favour of the Passivhaus standard as a reliable means of obtaining low-energy and low-carbon buildings and should be seen in the context that the estimated space heating demand of the average UK home is currently about 145kWhm2a 1 and a new build home predicted to be 50kWhm2a-1 and likely to be much more.