​The value of improved lots is to include the value of wells, septic tanks, landscaping, drives, and so forth. Conversely, the value of an unimproved lot should decrease at least by the cost of such land improvements. This reduction is normally referred to as the "vacancy allowance."

Vacancy allowances are to be individually calculated for different subdivisions or areas. All lot values should be calculated in a manner that will allow a deduction in the case of vacant lots and may be done by:

Percentage, where all contiguous lots are similar in size and physical characteristics, or

Flat amounts, where contiguous lots vary in size and characteristics and where a percentage reduction would result in an inequity.

The land assessment may not be itemized to show specific amounts attributable to the cost of individual land improvements.

It is extremely important that where an analysis is made of vacant lot sales, the resulting assessments should reflect that value after the deduction for normal land improvements. 1/

1/ Directive 8/30/74​​