If he rented less than 15 days in a year he does not have to rep

Used as a home but rented less than 15 days. If you use a dwelling unit as a home and you rent it less than 15 days during the year, its primary function is not considered to be rental and it should not be reported on Schedule E (Form 1040). You are not required to report the rental income and rental expenses from this activity. The expenses, including qualified mortgage interest, property taxes, and any qualified casualty loss will be reported as normally allowed on Schedule A (Form 1040). See the Instructions for Schedule A (Form 1040) for more information on deducting these expenses.

(IRS Pub. 17)