Is it possible to have a separate mortgage on a house to extend?

Kryza

Not had anything valued this is just looking into what routes i can take, so roughly house was mortgaged 5 years ago at 160000 wanting to add another bedroom and revamp bathroom and kitchen possibly adding 20000 in value, the loan is 15000.

DannyboyMidlands

So even if the house is still worth £160k (which could be unlikely depending on where you live) the the work will only just add enough value to pay for doing it. There's no chance of paying off your loan and/or increasing the equity as well. So you won't be able to remortgage. It's a non-starter I'm afraid.