Query on planning permission, etc,. for decking

[Handyman]

I'm going to make an offer on a house in Devon.
The house is an ancient (but modernised) 2 storey terraced house with a steeply terraced garden. Between the back of the house and set into the terracing is a single storey extension with a kitchen and study.
Question: If I wanted to deck over the top of the single storey extension at the same level as the adjoining terrace, do I need planning permission or building regs approval? What are the criteria in this instance?

 

[masona]

I know the answer in my area but Devon could be difference, your best bet is to ring Devon building control dept just to make sure before buying the property. You can get the phone number or details on their website.