Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 30·6.9
External solid walls
External solid walls must be designed to hold precipitation and release it during dry periods without water penetrating the building interior or causing damage; wall thickness depends on brick or block type and exposure to wind-driven rain.
An external solid wall should meet the requirement if it will hold precipitation until it can be released in a dry period without penetrating to the inside of the building, or causing damage to the building. The wall thickness to achieve this will depend on the type of brick or block and on the severity of the weather including wind driven rain. A method of describing the exposure to wind driven rain is given in BS 8104; see also BS 5628-3 and BRE Report 262 Thermal insulation: avoiding risks.
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