In DIN EN ISO 7783-2, façade paints are divided into three classes with regard to their water vapour diffusion flux density (V). The lower the sd value of a component, the greater its water vapor permeability, and class V1 paints have the highest water vapor permeability. If moisture enters the component layers below the façade paint, e.g. through water vapour diffusion from the interior of the building or through external weather influences, the more diffusion-open the façade coating, the faster the affected areas can dry out again. This reduces the risk of damage due to persistent component moisture.
Source: bauwion
