In general if the addition places your footage or BR count in top 25% of area, you will not have comps that depict a decent return.  

@Jasper Zimmerman no it is not normal at least not for me, especially for that square footage.

For the square footage, I can't speak for others, but we pull this data from the tax assessors office.  

Figure.com does (at least did do) automated appraisals that primarily uses the footage and location for valuation. 

For the cost of an ADU (~280k), you can put a down on a 20plex in another state for example.Hi everyone, wanted to share with you a great way to tap into the equity built from your ADU.The problem today: most appraisers used by traditional lenders would give ADU square footage a second-class treatment than the main house (as some of your mentioned above) since there aren't that many comps and they're trying to be conservative.However, you can consider taking out a HELOC/doing cash-out refi through Figure.com (HELOC up to $250k, Cash-out refi up to $1M).

Did you expand in the process or was your unit count/square footage good from purchase?

In my area $300+ depending on size and square footage of property.

. - It's likely that the health department will need to approve increased square footage if you lot utilizes a septic system.

maybe use infousa.com and search by businesses occupying a certain square footage .3. create a video so potential units can get a feel for the space and area without having to drive out and make an appointment to see it.  

Should I base my offer on the usable/occupiable square footage or the gross square footage (rentable square footage)?