I finally have a resolution to the question “is this building commercial or residential?” It’s important because the building codes are different, the permitting process is different, and the cost of trades like plumbing and electrical are different too.
It turns out that the answer depends not so much on the building itself, but on the use. If this building was to be used only by my wife and I, it would be residential. It would essentially be a disconnected extension of our home, where we could make art, have a piano, or install a pool table.
If, on the other hand, this building is to be used by other people, who will be paying us rent and who will need to have places to park and bathrooms to use that aren’t in our bedroom, it’s commercial.
I would have preferred to be classified as residential, but at this point, I don’t care which one it is, I just want to know. Now I know.
The thing that would cause the biggest trouble is if an engineer needs to do the mechanical, electrical and plumbing (MEP) drawings. It turns out that a master plumber can do the plumbing drawings, a master electrician can do the electrical plans. (And I don’t need to show mechanical since it’s just a window unit.) This is very fortunate since the project is so small I doubt I’d be able to find an MEP engineer who would take the project.
So this is progress, though I can’t think of a photo to include for it.