A rainscreen façade has been defined as a cladding applied either during the primary stage or as an over cladding to an existing structure in the following manner: “An outer weather resistant decorative skin fixed to an underlying structure by means of a supporting grid, which maintains a ventilated and drained cavity between the outer decorative skin (the façade) and the underlying structure”.
Panel joints are not normally sealed and a ventilation cavity of at least 25mm is allowed immediately behind the cladding panel. Allowance is made for water resistant thermal insulation to be positioned on the outside face of the inner walling.
Ventilation openings at the top of each clad area allow for evaporation of moisture vapour and at the bottom for ventilation and drainage.
A ventilated rainscreen incorporating insulation on the outside of cavity or solid masonry walls, will allow the building fabric to breath without the risk of interstitial condensation or structural decay. External wall insulation used in this way, is therefore, superior in performance since it eliminates the condensation risks associated with internal or cavity wall insulation. This is particularly important for over cladding refubrishment schemes.
In new construction the use of back ventilated rainscreen cladding provides the designer with the opportunity to use economical single skin load bearing blockwork for infill walls. The need for complicated dpm detailing is eliminated and there will be less risk of cold bridging.