Does EWI perform as a part of the airtightness of the building?

No. Although the adhesive and insulation layers may appear to seal the external envelope, the EWI system should not be relied upon as the building's airtightness layer. Airtightness should be achieved by the underlying wall construction and designated airtightness membranes or components, with the EWI system considered a separate external insulation and weather protection layer.