The three most relevant kinds of precipitation that effect the performance of a building facade are described as ˇ®direct', ˇ®splashback', and ˇ®runoff'. The determination of the intensity of direct rainfall on a facade is seen as the first step in understanding the characteristics of durability and performance of an external envelope. Away from the facade other indicators have been devised such as the ˇ®driving rain indices' by the NBRS, BRE and others. These can be used as a measure of severity at regional or local scales. In the field, and at the surface, vertical plate gauges can be placed at strategic locations and long term measurements estimated. There is generally a good correlation between the surface distribution of direct rain on a facade and the extent of maintenance problems, including material degradation, failure and appearance, as well as internal damage by water penetration. The long term nature of vertical plate gauge measurements detracts from its usefulness. This paper reviews methods of measurement of direct rainfall distribution at various scales. It introduces a method based on the geometry of surface deposits which allows a rapid comparison of facade performance, and indicates likely trouble spots.

• rain on walls, rain precipitation : map surface distribution
• wind driven rain