The impact of pressure equalization on watertightness of rainscreen systems

Many building components rely on pressure equalization to achieve a good performance in respect to water-tightness. There exist several guideline documents that provide the necessary geometrical constraints to achieve pressure equaliza-tion in a wall assembly but it appears these are only valid for dry conditions. To evaluate the likelihood of pressure equalization for a generic wall assembly during rain events an experimental setup was fabricated and subjected to a sinusoidal pressure loading with varying test parameters. A semi-implicit numerical model was developed and thereafter validated against the results for dry condi-tions. Results derived from simulations of pressure equalization under dry conditions may significantly overestimate the degree of pressure equalization of a wall assembly during rain events. In addition, the significance of pressure equalization in respect to fa-çade design was evaluated based on 6 case-studies. An analysis of several façade components indicates that current construction practice and guidelines are inadequate to achieve good pressure equalization of these assemblies. However, systems that have prov-en their performance in the field do not meet the requirements in respect to pressure equalization. Consequently, the impact of pres-sure equalization for watertightness should not be overrated.

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