Roof assemblies and below-grade construction share a common challenge: water wants in. Both systems require the architect to coordinate structural capacity, drainage pathways, insulation placement, and equipment loads into assemblies that work together without creating conflicts. On the ARE, this topic tests your ability to evaluate how decisions in one system propagate through the others.

A green roof illustrates the coordination requirement clearly. The growing medium adds 15 to 50 pounds per square foot of dead load, which demands structural verification before any other layer decisions are made. That structural decision then shapes drainage layer configuration, waterproofing membrane selection, and the placement of rooftop mechanical equipment. Every choice creates constraints on the next.

Below-grade walls follow the same logic. Where hydrostatic pressure is present, waterproofing replaces simple dampproofing, and a drainage plane combined with a footing drain becomes required. Insulation placed under a slab-on-ground must be high-density extruded polystyrene rated for 40 to 100 psi to resist compression loads. Getting insulation location wrong relative to the waterproofing membrane determines whether drying can occur.

The PPD exam tests integration, not recall. You will need to evaluate how a change in one variable, adding a green roof, switching from cavity to exterior insulation, moving rooftop equipment closer to the edge, changes the performance or requirements of connected systems.