Moisture excess represents the indoor humidity load. It is useful for assessing the moisture conditions of a building and as inputs for modelling and simulations. British Standard 5250 presents humidity classes which can be used to derive moisture excess values for dwellings. However, it is unclear how representative these humidity classes are for UK dwellings particularly as they were updated in the 2021 version of the standard. Thus, the aim of this study was to assess the levels of moisture excess in UK dwellings and compare them with the humidity classes. The analysis used secondary data from the IDEAL Household Energy Dataset and UK Met Office Integrated Data Archive System to calculate the average and critical levels of moisture excess in bedrooms, bathrooms, and living rooms. Preliminary analysis suggests that the critical levels of moisture excess for bedrooms and living rooms fall mostly within the British Standard 5250 humidity classes for dwellings, although a limited range of outdoor temperatures were analysed. As a sense check, the moisture excess was compared to values from literature. It was found that the average moisture excess was slightly higher than European equivalents generally.