Family home and Capital Gains Tax

I am planning to divide my family home and make two houses. I will live in one house and rent out the other. I will be borrowing to do the work.

What (a) is the most tax efficient way to approach this?
What (b) will my liability to Capital Gains Tax be if I sell the 2nd (i.e. Rental) house?

I may need to sell this as I have no pension.