Find yourself an architectural technician, you don't need an architect to draw up a loft conversion. Ask your local BC department if they have any contacts in the business - they may say no. Otherwise have a look on line at recent planning applications and you should be able to find one that way.
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loft conversions do not require planning permission. do not under any circumstances cut into the trusses you don't mention what type of property semi terraced or detached . I have designed and d done many loft conversions a little more info would help