SFRs to 4-unit properties still typically are looked at by lenders using the Sales Comparison method for valuation. Once you get beyond 4-units, then most lenders will use the Income Approach. Many will argue that 3-4 unit properties could also use the income approach, which is fine if you are determining the ROI for your investment. You probably already know this, but to calculate value using the income approach, you would first have to determine what yield other properties in the area are returning. This is your capitalization rate, or "CAP Rate". If you divide your property's Net Operating Income (NOI) by the Cap Rate (a percentage), that would give you a value. For Instance, let's say similar properties in the area go for a 6% CAP Rate, your property Grosses $200,000/year with $50,000 in expenses for an NOI of $150,000. $150K/.06= $2.5 million. I hope that helps.