We have an external porch area under the front eaves of our 70s bungalow which has been "built in" with a full length upvc window and frame on both sides to create an enclosed porch at some point. We are thinking of going a step further and replacing the upvc framework with a "proper" wall or stud. The area is narrow @ 1m wide by approx 2.75m. We will lose some of this width in constructing the wall but how much? What are our options apart from block with a 70mm cavity? could we use an external stud and insulate with kingpin or similar? Ultimately we need a decent level of thermal insulation as thin as possible as one of the use options of this area would be an ensuite to the front bedroom. What would you do?