What is 'combined protection' in waterproofing?

Combined protection involves using two or more types of waterproofing (Type A, B, or C) on a single structure. For example, building a basement with waterproof concrete (Type B) and also installing a cavity drain system (Type C). BS 8102:2022 recommends this for high-risk projects or where the consequences of leakage are severe (e.g., luxury apartments). It provides redundancy: if one system fails, the other protects the structure.