Driving rain is the horizontal component of rain that increases in dimension with increasing wind speeds. The quantity of driving rain (driving rain index) against a wall depends on the following influencing factors: precipitation rate, wind speed and wind direction, height above ground level, topography, obstacles and the roof overhang.
Components that are exposed to driving rain, such as windows, are tested for tightness against driving rain (also referred to as driving rain impermeability) in a laboratory. The objective of this test is to localise weak points in constructions before installation in the building structure. This allows deficiencies to be corrected in advance, as well as allowing the collection of data about new systems.
Resistance against penetrating water
The tightness against driving rain is a measure of the resistance with which a window withstands the penetration of water into the inside of a building at a given wind strength, rain quantity and stress duration. There is not necessarily any correlation between air permeability and tightness against driving rain. For tightness against driving rain, the type, arrangement and construction of the seals and folds and the pressure ratios in the construction that can be regulated by pressure equalization and drainage openings are decisive. The test for the tightness of a window element against driving rain does not include the building structure connection.
On the outside, a sealing system, tight against driving rain, that is as permeable as possible (<Sd) must be selected. Correctly installed pre-compressed sealing bands are the preferred system for the outside seal. Only a degree of compression of 20% of the initial thickness guarantees tightness against driving rain.
The requirements for tightness against driving rain, resistance against wind forces and air permeability of the joints are closely connected to the heat protection in accordance with EnEV. The previously applicable DIN 18055 was replaced by the European standard DIN EN 12208, which now regulates the requirements for tightness against driving rain.