Identify where the problem begins. Physical deterioration concerns wear or damage. Functional obsolescence concerns the property's usefulness or design. External obsolescence comes from outside influences. The official appraisal glossary separates these causes.

A worn roof suggests physical deterioration; an awkward layout suggests functional obsolescence. An adverse neighboring use illustrates an external influence, if market evidence establishes a loss in value.

Classify the cause before deciding whether correcting it is practical or economical. Do not assume every old building is poorly maintained. Review the Chapter 17 appraisal guide; this is valuation vocabulary, not a tax deduction.

Start the free 63Hours course