What is a common requirement for exterior insulation in terms of its depth below grade?

The requirement that exterior insulation must be at least a specified depth below grade is essential for protecting the building's foundation from moisture and ensuring effective thermal performance. Installing insulation at this depth helps to prevent thermal bridging, which can lead to energy loss, while also safeguarding against water intrusion that could compromise the integrity of the structure.

When insulation is placed at a minimum depth of 12 inches below grade, it helps ensure that the foundation is well insulated against ground temperatures that can fluctuate and cause issues for the structural materials of the building. This depth provides an ample buffer to manage soil moisture and temperature variations effectively.

Other options may suggest incorrect depths or coverage that do not align with common building codes or best practices for foundation insulation, leading to potential building performance issues or code violations. Thus, the guideline for maintaining a minimum depth of 12 inches is rooted in both preventing moisture problems and maximizing energy efficiency for the building's overall performance.