My examiner suggested the following scenario:
Pull median income for the tract in question. Use 80% of this figure. Now take 30% of that figure and attribute that to housing costs. How do the rents (from your rent roll) compare with your multi-family properties?
$50,000 Median Income
$40,000 (80% of Median = Moderate Income)
$12,000 (30% of Moderate Income)
$ 1,000 Monthly Rental Expense
$ 700 2 Bedroom Rent in your complex
Rents are affordable to low and moderate income renters.
Now throw in your market experience. Does the borrower focus on low and mod properties to pick up transient renters, military staff, etc.? Would a cheep bank examiner choose to live in the $700 apartment? Sure some would, but if you can support, with your market knowledge that the property really has a high focus on low or mod income residents (ie take some pictures!) and it's affordable, you should get credit for the property.
If the property is in a middle or high income neighborhood you'll need to show that the rents are actually held for low or mod income people (ie section 8, LIHTC, etc.) If you can't show that, you can probably assume some cheep bank examiners live in the units
and it's not CD.