This is addressed in the commentary to Reg Z under exemptions. Banks should cover this in credit policy and train lenders.
4. Non-owner-occupied rental property. Credit extended to acquire, improve, or maintain rental property (regardless of the number of housing units) that is not owner-occupied is deemed to be for business purposes. This includes, for example, the acquisition of a warehouse that will be leased or a single-family house that will be rented to another person to live in. If the owner expects to occupy the property for more than 14 days during the coming year, the property cannot be considered non-owner-occupied and this special rule will not apply. For example, a beach house that the owner will occupy for a month in the coming summer and rent out the rest of the year is owner occupied and is not governed by this special rule. (See comment 3(a)–5, however, for rules relating to owner-occupied rental property.)
A "commercial loan" is whatever the applicable definition says it is. Without knowing the context in which the question arises, there's no way to provide an exact answer.