Deterioration
Wear from age and use. Split between what should have been repaired already, what will need replacing before the building's economic life ends, and what lasts as long as the structure.
Curable, deferred maintenance
Items needing immediate repair or replacement to meet functional standards and appeal to buyers. Measured at cost to cure, which can exceed the original installation cost once removal, disposal and unexpected complications are priced in.
Incurable, short-lived
Components not yet due for replacement at the effective date, but which will need replacing before the building reaches the end of its economic life. Partially depreciated using an age over life ratio applied to current cost.
Incurable, long-lived
Everything that is neither deferred maintenance nor short-lived. Exterior walls, structural framing. Assumed to share the building's age and life expectancy and not to require replacement within its economic life. Takes the effective age over total economic life ratio applied to residual replacement cost.