CGT on a property 'built' within my property

In 2021/22 I separated my main residence, with some additional building work, from a 3 bedroom detached to a 3 bedroom semi detached with an additional 2 bedroom semi detached. I am now considering selling the 2 bedroom semi, which I have rented out for 2 1/2 years, declared and tax paid. Would I be liable for capital gains tax? Would the taxable amount be on profit, i.e less building costs & loans, or on the total saleable value? Would I be liable for any private residence relief? As I have devalued my main residence that I live in.

Hi,
Yes you will be liable to CGT on the 2 bed house. no private residential relief is due as this 'new build' has never been your own house.
The gain will be due on the difference in dispoal price and the cost to build.
You cannot deduct any mortgage/finance still outstanding.
Thank you.