Why are façades ventilated?

Façades are ventilated to prevent moisture behind the cladding from remaining permanently within the construction. The air cavity between the thermal insulation and the outer façade layer allows air movement that can remove rainwater entering behind the cladding and moisture arising from building-physics processes. Rear ventilation therefore supports drying and the long-term performance of the external wall build-up.

In a ventilated rainscreen façade, the cladding provides the primary protection against driving rain and mechanical impact. However, it should not be treated as a completely watertight layer. Small quantities of moisture can enter behind the cladding through joints or interfaces. Water must therefore be able to drain in a controlled manner, while residual moisture can dry through the ventilation cavity. The thermal insulation is structurally separated from the weathering layer and can continue to perform its intended function.

Performance does not result from the cavity alone. Air inlet and outlet openings, free cross-sections, cladding joints, the position of the insulation and structural restrictions must be coordinated. Fire barriers or substructures must not interrupt the intended airflow without being considered in the design. Interfaces at windows, plinths and parapets also require clearly defined water drainage.

Rear ventilation does not replace a proper thermal, fire or moisture protection assessment, nor carefully designed details. It is one element of the overall building-physics concept of a ventilated rainscreen façade. A permanently open and controlled airflow path must therefore be secured from the detailed design stage onwards.