Ok, so here's this:
Outside of that specific situation, here are some guidelines for what types of rental or royalty activities are considered a trade or business. If you are renting property that requires very infrequent interaction with the tenants and maintenance to the property, the courts have generally found this type of activity is not a "trade or business". On the other hand, if you rent out property that requires frequent tenant interactions or maintenance services, this type of activity is generally classified as a "trade or business." (See examples later of activities that would or would not typically be treated as trades or businesses.)
At least one of our rentals, being on the same property we own, falls into that category, as we interact with them daily, pretty much and, property is maintained regularly. Another rental was less intensive interactions, yet, quite a few of them plus regular maintenance done by me/us.
