Design and construction recommendations to improve impermeability in rainscreen walls built with natural stone coverings

In current European construction, the building model of stone coverings detached from the building support is being increasingly used. These coverings remain joined to the rest of the façade only by certain anchorage points, leaving thus a cavity between the stone panels and the inner support. This is the model that best adapts to the actual concept of heterogeneous façade, with high performance qualities and predictable behaviour.Walls designed to achieve a high degree of air pressure equalization between the inner cavity and the exterior, obtaining considerable benefits, are known as Pressure Equalized Rainscreen (PER) walls. Existing design guidelines on these walls are mainly qualitative and referred to a theoretical continuous wall, with few references to real construction methods or discontinuities of the façade.Behaviour of PER walls, when built with stone panels of medium thickness (30–40 mm) and open horizontal and vertical joints, is analysed in this study, based on the climate in the city of Valencia (Spain). Although panels of 12–20 mm thickness are often used in many countries, the Spanish Technological Standards recommend using panels of at least 30–40 mm in this type of façades, being thus this thickness the most common in Spain. The aim of the study is to understand rainscreen wall performance in this case, with regard to water coming into contact with the façade, and thus propose several design and construction recommendations to improve impermeability in crucial points of the façade.

Research highlights
► An adequate drainage system in stone panels always reduces rainwater penetration.
► Non-plane panel edges are notoriously beneficial only with joints of small width.
► Influence of panel thickness in water penetration is insignificant with joints >8 mm.
► Practical recommendations based on tests and existing design guidelines are proposed.