Retrospective applications will usually cost you about 20% more than standard fees I would advise you contact your Local Authorities Building Control team for further advice/confirmation. They will propbably request that you expose certain elements to prove methods of construction (e.g. lift floor boards, roof space). If you need wish to discuss further or need require a price for any detailed drawn plans etc please contact me 07877 384870 or see web www.overflowcad.co.uk .