Looking for the most tax efficient method of doing this, I will have a mortgage on this property, LTV <50%. The monthly repayments will be 900 over 12 years, am aware I don't have to register with RTB, but then I can't claim the interest on mortgage against my tax liability, house is not in a RPZ. Any advice as how to minimise tax? Son and his partner will be residing in the house. Not sure how much rent I would charge him but was thinking about 800 pm.