Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 31·6.13
External cavity walls moisture prevention
External cavity walls must prevent precipitation from reaching the inner leaf through either a drained air space or equivalent means.
An external cavity wall should meet the requirement if the outer leaf is separated from the inner leaf by a drained air space, or in any other way which will prevent precipitation from being carried to the inner leaf.
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