Among appraisers, this is a highly debated matter. Some swear by the cost approach, others swear it can’t work. Institutions like FHA/USDA require it 100% of the time, while the VA does not. Some lenders require it (though it would appear that this is possibly for insurance purposes more than valuation). This is an attempt to look at the strengths and weaknesses of the approach. First lets look at the underlying assumptions:
Cost (and income for that matter) approach is a derivative valuation methodology. Without the sales comparison approach, the cost approach can not exist. This is important to note, as this derivative data will be more prone to error the further it is removed from the primary data.
Cost approach assumes accurate builder costs. The collection of cost to construct data is a time consuming matter which is why appraisers often use cost guides like Marshall and Swift. There are a few areas of concern here. A) That the costs for the region are calculated accurately. In our rural areas, new construction is rare, with the cost of renovating a home being far below that of new construction. So, where does the data come from in these rural areas? B) That the equalization factors are accurate. In truth, THIS is how those regional costs are calculated - by taking state and national cost averages and multiplying them by a regional factor. However, again, with limited cost data, how can an accurate multiplier be calculated? C) That time factors are accurate. Again, this suffers the same issues as above - however, also suffering that data is always backwards looking in its accuracy - from 2016-2019 builder costs have spiked, in some cases materials have seen a 20% increase, and yet in our markets sales have remained flat. Finally, these errors multiply, seriously weakening the model.
Cost approach assumes accurate total economic life models. Marshall and Swift (a common cost estimator) gives no economic life above 65 years (Excellent quality, masonry home). Compare that to the dozen homes that are outside my window at this moment - homes of average quality, non-masonry (55 years by M&S) that have received only roofs, painting of the wood siding, and the bare minimum of updating to the interior in 1960 and yet have 30+ years of remaining economic life - yet are 114 years old. A polling of appraisers found realistic total economic lives of properties of this quality to range from 120-150 years. Yet M&S remains an industry standard? IF appraisers are to use the cost approach in a credible fashion, a radical divergence from the Marshall and Swift methodology is necessary.
Cost approach assumes accurate effective ages. This is a purely subjective opinion based on sensitivity analysis. While this is not uncommon in the appraisal profession, it is sometimes presented as far more black/white factual than it truly is. Given that depreciation is based solely on 1) accurate builder costs which we see issues with, 2) accurate economic life models which are notoriously inaccurate, and 3) accurate effective ages which are a subjective analysis, we see that depreciation is fraught with possible error.
This is a serious stack of possible compounding errors that strike directly at the overall validity of the cost approach. Add to this the possibility confirmation bias to simply confirm the sales comparison approach indication. So, what is the cost approach good for?
Contributory percentage to the whole. If we can validate the cost approaches relevance to market participants motivations, then the percentages of un-depreciated contribution of certain elements (bathrooms, below grade finish, overall quality, GLA) could theoretically be supported through this model without having to wade into the multiplying errors of points 3 and 4 above.
Affects of condition (effective age) on the whole. Again, if we isolate only this factor, without multiplying possible errors, we can see what effect 10 years of depreciation would have on the overall value of the home, and derive support for condition adjustments from this.
Age adjustments. If we can perform a series of cost approaches in a market vs. those same home sales, with an understanding that effective age is a factor of condition AND age, and find a way to tease these apart, then the result that would emerge would be the depreciation per year of the home. It should be noted however, that in teasing these two factors apart, a paired sales analysis would have to be performed in order to extract the condition adjustment before determining the depreciation per year.
Anytime that we use multiple parts of the cost approach however, we are introducing the possibility of error into the approach. However, that is true of ALL approaches to value. The more factors adjusted for in the Sales Comparison approach, the more possible errors- the strength of the sales comparison approach is bracketing. If all amenities are bracketed, we have greater confidence in the final range, with weighted analysis coming to a final conclusion. We have no such tool in the cost approach. Within the Income Approach, we become increasingly concerned with more and more adjustments (increasing gross percentages). If all factors are bracketed we have greater confidence in the output GRM range, with weighted analysis coming to a final conclusion. But with the cost approach, there is no bracketing, and therefore is the weakest of all of the approaches to value. It is very likely that in the future, this approach will be retired.
Of all of the approaches to value, the cost approach is probably the most open to error, confirmation bias and abuse. Even in new construction, the cost approach CAN NOT inform the appraiser of what the market is willing to pay apart from the sales comparison approach, and as a result serves a limited value. Cost approach serves a purpose in possibly extracting contributory value in difficult markets (though we have seen absurd data such as $3,000 contribution for a full bathroom in a $750,000 home, which the sales data and any real estate professional does not support). The cost approach is a severely limited tool, but good if used properly. A hammer is a very effective tool - just don’t use it the wrong way, you’ll just look silly.