OK, so what does the Cost approach tell appraisers (at least, those who are willing to listen) about the market? The listening is in the analytics.
Consider, first of all, the site value as if vacant. This is a separate appraisal within the appraisal. If the appraiser does not know to a professional certainty the value of the subject site as if vacant, how can that appraiser adjust the comparable sites (as if vacant) to it? It is ironic that, to adjust the comparable site’s value to that of the subject, the appraiser must know, to the same certainty, the value of the comparable site as if vacant, too. Assuming three comps and a listing, then the appraiser goes thru this site-as-if-vacant analysis five (5) times. If the appraiser is listening, an analysis five (5) sites deep will tell the appraiser an abundance about a market.
Now, consider the entrepreneurial incentive/profit aspect of the analytics of the Cost approach.
Too many appraisers have fallen into the trap of saying there is not such a profit or incentive in the cost approach since the sale of the property is from one retail buyer to another. It is not a sale from a builder/developer to a retail buyer. This is true. It is true, yet it is also thunderously irrelevant. An appraiser builds the house new on paper. Don’t new houses sell (hopefully!) at a profit from the developer/builder to a retail user? Since it is physically impossible to construct a used house, the analytics of the Cost approach assume a new house first. Therefore to estimate the reproduction or replacement cost new of a house and not include an entrepreneurial incentive or profit is to fail to take a step the market commonly takes. How reflective of the market is that?
For grins and giggles, assume a 15% entrepreneurial incentive to the cost new before any depreciation. This is a trail balloon the appraiser floats to see if there is such a reward in the market. If the market will not pay such a reward there is, by definition, an external obsolescence factor in the market. This is a market condition which the appraiser has an obligation to describe within the report. Yet, if the appraiser is not willing to measure the market to see if such a reward is present, how can s/he report it? The analytics of the Cost approach show if such a reward is present. The analytics of the Sales Comparison approach do not and cannot.
A blog such as this one is not the time or place to present a long article on calculating depreciation. The point is that while FannieMae, et al, no longer require a Cost approach to be part of an appraisal report going to them, whoever said the analytics of the Cost approach should not be part of an appraisal? FannieMae surely did not. How can an appraiser listen to, and then interpret the market, if s/he ignores two-thirds (Cost and Income approaches) of what it says?