I have this same question.
100 year old homes in old town/down town have commercial zoning (originally constructed as sfrs). Some parts half the homes are sfrs and the other half are small hair studios, insurance office, or other misc office type space. The only difference between the buildings are a wheel chair ramp and a few parking spaces (usually enough room in the front yard/lawn area for pavement). The interior of the” commercial” properties are not structurally modified and usually have a few interior walls removed.
Sometimes commercial use sells for a little more, but sometimes not (very few sales in these mixed areas).
It seems to me like the highest and best used question is not “is the value of the property higher as vacant commercial lot vs legal non conforming SFR use”. The question is “what buyer would pay a higher price? The owner occupant or the investor or small business man who will spend 1-5% of the purchase price to use the SFR building as a commercial property?
Am I incorrect here? Seems to me like I would need a commercial license in order to establish a value of the property being commercial even though the current structure is a single-family home.
To those of you, that would say the modifications come in to play… What if a single-family home has the wheelchair ramp and the parking spaces in the front but is currently occupied by family. Current use is single-family, residential, but current set up would allow either single-family occupancy or a small office type situation…