There is one assessor's office that actually has a quality rating system that utilizes more than 20 different quality ratings...
California? The assessor's handbook uses 10 quality class designations and half steps between them. For each category of homes (pre-1900 and post-1990)
QUALITY CLASSIFICATION Quality class ranks buildings according to their amounts of materials, grades of materials, and workmanship. If two buildings are of the same design type, construction type, shape, and size, but one has more materials or better materials, it will have a higher square foot cost. Also, if two buildings are exactly alike, except that one was built with greater care and skill, it will be of AH 531.10—Costing Information 6 January 2015
better quality and will have a higher cost.
Of the five choices that lead to the overall classification of a building,
the choice of a quality class is the most difficult. The relative quality of a building is not as obvious as its design type, construction type, shape, or size. Many points of reference must be observed. Many parts of a building cannot be seen, and their presence and nature must be inferred.
The quality class designations are usually numbered from 1 to 10. A class 1 building is the least costly to build per square foot, and a class 10 is the most costly. They are assigned on the basis of a comparison to numbered descriptions (specifications) of typical buildings of various quality levels.
The specifications for each quality class make a distinction between classes. This distinction often shows in the quality of a feature and not whether the feature is present. The same feature may exist in different classes, but the quality of the feature will help to determine the classification. Conversely, some features may be included in a particular classification, while in another class, the same feature must be treated as an additive.
Each chapter of this handbook dealing with different design and construction types contains a set of applicable specifications.
The building specification charts found in the various chapters are a compilation of attributes typically found in the building class listed on the individual charts. Not all structures will include all of the typical attributes listed in a particular classification. That does not automatically mean that it is an improper classification. The appraiser must use judgment to determine if the majority of attributes listed pertain to the structure being classified.
Many times buildings have quality features that fall between those of two classes rather than being most like one or the other. For this reason, half-class gradations are used. For example, buildings can fall in the 5.5 class or the 6.5 class. The unit cost of a class 5.5 is halfway between the cost of a class 5 and the cost of a class 6. The square foot cost tables array costs for half-classes as well as for full classes.
The typical attributes listed in the specifications are the basis for the cost factors established in the square foot area cost tables. These factors recognize and include an element of cost for the typical attributes. The factors do not, however, include costs for additives.