I've highlighted (from Mike K's post) the significant drivers related to physical deterioration and effective age:
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Here are some concepts:
Long Lived Items: A building component with an
expected remaining economic life that is the same as the remaining economic life of the entire structure.
Foundation and roof structure would be examples of long-lived items.
Short-Lived Items: A building component with an expected remaining economic
life that is a shorter than the remaining economic life of the entire structure.
Paint, appliances, wall/floor finishes, roof covering, HVAC, plumbing fixtures, etc., would be examples of short-lived items.
The condition ratings are largely based on Total Economic Life vs. Effective Age. Chronological Age, while a consideration, is not the driving factor. A home built today, if just maintained and not renovated, may have a Total Economic Life of 65 years. What this means is that at the end of 65-years, the expectation is that the long-lived items are in need of replacement.
Regular maintenance can slow down the "aging" process but not stop it. As time goes on, my effective age continues to get higher and my remaining economic life continues to get shorter.
Replacement of short-lived items can further slow down the aging process and actually set it back. Once items are replaced and I continue to maintain the home, my effective age may be reduced and my remaining economic life may be extended.
Renovation of short-lived and long-lived components significantly sets back the aging process. Once I renovate, I can turn my effective-age clock back significantly and I've extended the remaining economic life significantly.
When a house has been thoroughly renovated, both long and short-lived components have been brought to a "new" condition. This is a C2; the only difference between a C1 and C2 is C1 is newly constructed, C2 is similar to newly constructed.
If an improvement has an estimated life of 65 years, once renovated to the C2 condition, it is like the clock restarts. This is the fountain of youth for a house. A C2 house with a chronological age of 75 could reasonably have an effective age of 1-5 years. What this means is, that after the major renovation, the house, if properly maintained afterward, should last for another 60-64 years.
In a C3 house, some (but not every) major component has been renovated and the structure ( a long-lived item) is well maintained. This is a trip to the anti-aging clinic. Most of my interior finishes have been redone, it is likely that my major components (kitchen/baths) have been renovated. I probably have a new roof, windows, and heating/cooling. A C3 house could reasonably have an effective age of 10-20 years. There is a wider range here, because not every component need be renovated and some components are more significant (a major kitchen renovation is more significant than refinishing/replacing the flooring) than others. So, my C3 house with a chronological age of 75 could reasonably have a remaining economic life of 45-55 years.
C4 means that some short-lived items (flooring, paint, maybe a bath renovation) have been replaced but many of the remaining components have not; they are near the end of their physical life (which means they are getting near to be replaced) but they still function adequately (they can still be used). This is someone who goes to the doctor readily and maybe walks 3-miles a week. The improvements have been maintained and there may be some minor repairs required. C4 homes (in my market) are entry level homes or homes that someone will purchase with the intention of upgrading/renovating some time in the future. Or, they could be a rental (I'm not going to pour a lot of money into the improvements because I cannot get it back in rent, but I want it clean and working so I can get top rent). So, my C4 house with a chronological age of 75 may have an effective age of 40-50 years and a remaining economic life of 15-25 years.
So, the "C" condition is directly related to remaining economic life. The level of improvements/renovations/remodeling will determine where on the scale of the "C" ladder a house will fall within.
While the definitions are designed to be objective, and appraisers can avail themselves to recognized & published tables summarizing what the projected Total Economic Life of an improvement is (based on the quality of materials; which is different than the condition of those materials),
in the real world of residential appraisal, the estimation of effective age has a degree of subjectivity to it.
A. The appraiser looks at the house and relies on a published table for en estimate of total economic life. Assume that table indicates 65-years for a subject-like constructed home.
B. Based on the condition (how the property has been maintained) and on the level of renovations/upgrades (what has been replaced or renovated), the appraiser concludes the house is 35% through its total economic life; this means it has 65% remaining economic life.
C. 35% of 65 years is the effective age; "effective" because it reflects how old the improvement is based on the total economic life span. 35% x 65 = 23 years. Effective age is an economic concept when measured against total economic life. Remaining economic life is the estimate, in years, of how long the improvement, as-is, will continue to add contributory value to the land. Once there is no more economic life remaining, it is the improvement no longer contributes value to the land. One would either demolish the improvement or significantly renovate/remodel it to set-back the effective age clock.
There are ways to measure depreciation which are much more detailed than the above. But as I said, in most cases, this is how effective age is estimated for a typical residential appraisal.
There are other forms of depreciation that can effect remaining economic life: functional issues (a small, galley kitchen in a market that demands larger kitchens due to modern standards) would also reduce the remaining economic life of a property. But, if renovated/remodeled and it were financially feasible to do so, that functional issue would be corrected.
Does that help?