A loan on which of the following properties would not be subject to the requirements of RESPA?

RESPA, or the Real Estate Settlement Procedures Act, is designed to ensure that borrowers are informed about the costs involved in the real estate settlement process and to protect them from abusive practices. However, not all loan types are subject to the requirements of RESPA.

In the case of a loan secured by a single-family residence that is used strictly as an investment property, it is exempt from RESPA's requirements. RESPA is primarily concerned with residential mortgages where the property serves as a primary residence, such as a single-family home or units intended for primary habitation. An investment property, by contrast, is typically utilized for generating income rather than for personal occupancy.

The other options involve properties that are designed for living purposes: a duplex where the owner occupies one side, a three-unit property being used as a primary residence, and vacant land intended for the construction of a home. These are all considered residential properties under RESPA's jurisdiction, meaning the loans on these properties would require compliance with the act's regulations regarding disclosures, good faith estimates, and settlement practices.

Thus, the correct identification of the investment property is what distinguishes it from the others, making it not subject to RESPA requirements.