Section 1407 establishes water-resistance requirements for exterior walls and building envelope. Water-resistive barriers including felt, synthetic materials, or foam sheathing prevent liquid water intrusion into the building. Drainage planes direct water down and away from the structure. Flashing at all penetrations including windows, doors, utilities, and mechanical attachments prevents water from running into the building. Proper slopes on horizontal surfaces direct water away. Caulking at joints seals gaps preventing water entry. Below-grade walls must include waterproofing membranes and drainage systems. Vapor barriers on the interior side of exterior walls prevent condensation in cold climates. Vapor-permeable barriers allow moisture to escape while preventing liquid water entry.