Enter an typical life here (and an effective age in the previous field) ONLY if you want to depreciate the majority of the components in section differently than the overall depreciation percentage set on the Building Data screen.
If you leave this field blank, Residential Estimator automatically sets the depreciation percentage for the components in the section to the overall percentage set on the Building Data screen.
You can set the age and life, or the depreciation percentage, for individual components to override the value you set here.