Actually FNMA and FHLMC make the rules. The mortgage lenders monitor compliance to insure that the mortgages that they make are salable in the secondary market. Any residential real estate that is not the owner's principal residence is classified as either a second home or an investment property in the real estate financing arena. The difference in interest rate and qualifying criteria is fundamental.
Whereas, second home mortgages normally require a small add on to the closing fees above a primary residence mortgage, investor loans require an interest rate premium of 5. to.75% and even more depending on the size of the down payment. The one qualifying advantage an investment property loan bestows is that the projected rental income (minus a 25% vacancy and maintenance factor) can be used as income to offset the mortgage payment. The second home mortgage requires that the applicable qualify for the entire mortgage payment in addition to the mortgage on the primary residence as well as any other monthly debt.
So what is a second home according to the lender? To begin with, the property must be located a reasonable distance from the borrower's principal residence. Underwriters have some discretion with this issue but normally require that the property be located 50 to 100 miles from the primary residence and require the borrowers to justify the purchase of the property as a second home. The purpose of this annoyance is to insure that the intent is to occupy the property on a frequent basis, not simply to avoid investment property interest rates. Buyers do not normally purchase investment real estate located a substantial distance from home.
This does not preclude the borrower from renting the property to others but there are rules as to the terms. The rules state that the borrower must have control of the property; meaning that the property will not be listed with a management company and the borrower will not execute a rental agreement. The promise for this requirement is that statistics indicate that owner occupied properties are better maintained; therefore reducing risk to the lender. If the owner is occupying the property for a portion of each year, theoretically there is less chance that the property will deteriorate to the point where it loses value.
These rules are nebulous at best. There does not seem to be any practical way to enforce them pending to loan closing. If circumstances arise promoting the purchase of a primary residence change and the owner is either forced or elects to convert it to a rental property, the lender has no recourse against the borrower. There is a direct correlation to the primary residence and the second home purchase. It all comes down to the intent at the time of loan closing. Many properties purchased as second homes will eventually become rental properties.
There are circumstances where a purchase does not fit perfectly into the second home category but meets the underwriting criteria. Parents frequently purchase real estate to provide housing for their children to occupy while they are attending college. This can be a practical alternative to paying rent and hotel expense during their visits. While this scenario is not exactly the objective of second home financing, it does fit the underwriting parameters. Interestingly, this property will not likely be a second home forever. When the education is completed or discontinued, it is likely to become an investment property but purchased at far less expense to the buyer.