The Climate Change Risk Assessment 3 (CCRA3) identified several different climate hazards that can damage building fabric. The integrity of buildings is affected by moisture ingress, which can cause mould, materials decay and frost damage. In extreme cases, excess moisture accumulation within the building fabric can lead to mechanical failure of the structure. Wind-driven rain (WDR) is the primary source of moisture load for walls. This risk requires further investigation.

ISO 15927-3:2009 specifies two procedures for estimating the quantity of water likely to impact on a wall of any given orientation. This information was based on an older standard (BS 8104:1992) which in turn used rainfall annual exposure maps published in 1976. It is believed these maps were created using data from a small number of weather stations. This information therefore requires updating.

Wind-driven rain can be quantified using a metric I from ISO 15927-3:2009 which has units of volume per unit area and time (here, litres m-2 s-1). This metric was calculated on hourly timescales and is a function of rainfall amount, wind speed, wind direction and wall orientation. Larger values of the metric imply more wind-driven rain striking a wall. The equation which will be used to calculate I yields the amount of WDR passing through a vertical surface in an undisturbed air stream. It does not take into account of any effects of local topography or the building itself on the air flow and hence the amount of water striking a surface.

The UKCP18 climate projections include an ensemble of 12 simulations executed at a resolution of 2.2 km, referred to as UKCP Local. These data have been aggregated to a 5 km grid on the OS National grid; the 5 km data were used for this project. Hourly rainfall totals, wind speeds and wind directions are available from UKCP18 Local.