Every exterior wall must answer three questions: How does it keep water out? How does it manage heat flow? And what happens when the first line of defense fails?

The answers produce four distinct assembly families that appear repeatedly on the ARE. Cavity walls physically separate the outer cladding from the inner structure with an air gap that collects water and drains it outward through flashing and weep holes. Rain screen assemblies go further by equalizing air pressure across the cladding so that the pressure differential that drives water inward is eliminated at the source. Curtain walls hang from the building frame as a non-structural glazed or spandrel panel system, transferring all wind and gravity loads to the structure but carrying none of the building's floor or roof loads. EIFS (Exterior Insulation Finish Systems) wraps the building in continuous rigid insulation covered by a polymer finish coat, minimizing thermal bridging but demanding precise moisture detailing at every termination and penetration.

Each of these strategies has a characteristic strength and a characteristic failure mode. Cavity walls drain water effectively but require continuous flashing and weep holes or that drainage path collapses. Rain screens prevent water from being pushed in but require a well-detailed inner air seal to achieve pressure equalization. Curtain walls are fast to install and architecturally flexible but thermally vulnerable at mullions. EIFS provides superior thermal performance but traps water if the outer coating is compromised without a drainage layer.

Understanding which system fits which project context is the ARE objective: selecting an envelope assembly based on cost, climate, program requirements, sustainability goals, and regulatory constraints, then evaluating how that selection shapes the rest of the design.