What Is An Fha Loan Mortgage Fha 4 Plex Guidelines Fha 4 Plex Guidelines. The FHA keeps a book of rules and says, "so long as you. – FHA-insured Mortgages on principal residences and investment properties, and exceptions to the FHA policy limiting the number of mortgages per borrower. FHA 2-4 Unit info. fha loans can be used to purchase 2, 3 or 4 Unit properties. Many other California counties are eligible for higher FHA loan amounts for FHA 2, 3 or 4 plex purchase and refinance. Here is a complete list of California Counties and their FHA.