Reduced Rate VAT on Barn Conversion

I have a client who is converting a barn into a furnished holiday let, can he be charged 5% VAT rather than 20% VAT?

The barn is designed to be a dwelling but the planning states that it is a FHL. According to HMRC CA manual (CA11520) there is no definition of a dwelling house so it takes it's ordinary meaning. It then goes on to say that "a person's second/holiday home or accommodation used for holiday letting is a dwelling house". Although this is for purposes of capital allowances, could I not use that definition to argue the same for VAT?