This sort of query (family member, possibly already a home owner, helping another family member out to buy a place of their own) seems to be cropping up more and more over the past few months/years. If you browse back through the contents of this forum and the Mortgages and House Buying forum you will probably find some topics of interest/relevance. In general terms note that if your name are on the deeds (as opposed to simply providing financial assistance) then your sister will lose her first time buyer status by virtue of the fact that all parties involved are not FTBs. This will have a bearing on stamp duty and mortgage interest relief. You should carefully consider the tax implications (e.g. stamp duty, income tax, CGT) of your sister being an part owner occupier and you being a non part owner non occupier de facto investor. If in doubt get independent, professional advice.