CGT on adding my son as joint tenancy by transferring less than 50% of equity at nil cost.

I have a rental flat which is my only property. I don’t live there and not likely to, It’s mortgage free and I would like to continue to receive rent. I would like to add my son as joint tenant. Is there minimum % of equity (say 10%) I need to transfer to make it joint tenancy? Would the property automatically transfer to him on my death. If I die before 7 years will the IHT be tapered on just say the 10% value.

Hi
There is no minimum but as this is not your main residence, this may be seen as a disposal and may be liable to capital gains tax.