No, it does not qualify as investment property at this point in time. The IRS would recharacterize the house as a second home because the son paid no rent or expenses.
He could have treated it as investment property had he charged the son fair market rent, but unfortunately he didn't, or if he held the property without letting a related party stay in the house rent free.
However, we now have Revenue Procedure 2008-16 that covers this scenario. Vacation homes and second homes can now be 1031 exchanged if:
- The property is owned for at least two (2) years
- The property is rented for a minimum of 14 days for each of those two (2) years
- The taxpayer's personal use of the property is limited to no more than 14 days each year or no more than 10% of the number of days that the property was rented