What makes the embodied energy of a building a “sunk cost”? It’s a cost that must be built into the budget but doesn’t relate to a specific budget area.

It’s the kind of cost that can only be assessed through careful analysis of the existing structure.

It’s a real cost that has already been paid in the past and so doesn’t represent a present expense.

It’s a cost that can surface in the budget unexpectedly without attention to energy efficiency.