Building thermal modelling packages require weather data to predict representative internal conditions. Typically, around the world, reference weather years of various forms are used which are created from observations at aparticular location. However, it is unlikely that this location is identical to that of the building. This can lead toweather files for coastal locations being applied to inland and upland sites or vice versa. In the UK, the UKCP09 weather generator has the ability to produce weather at a 5 km resolution. Currently, it is unclear how useful this extra spatial resolution will be and it is this question that is addressed here. It is found that for both future and present climate, the spatial variability of the weather is the dominating factor. Although there are geographies where a low spatial resolution can be used, there are regions where a much higher resolution is necessary.