Actually, if you really plan to continue to let him live there rent free, he would get a much better return on his investment by putting his money elsewhere and letting it grow. Rarely does a house investment beat market investments over a long period, especially when you factor in maintenance, insurance, and repairs. A house is mostly a good investment because it replaces escalating rent (and small incremental appreciation), but he doesn’t seem to have that risk. Perhaps you explain it to him this way and he will agree, investing in YOUR house isn’t a great plan. However, I’d never let him live there rent free. And rent doesn’t give him ownership.