This planning proposal is to change the existing damaged extension from double pitched rood to flat roof, while not increasing the top height of the extension. The top height of the new flat roof will be the same as the top ridges of the existing double pitched roof.
The new roof of the extension is going to be flat and placed at the same height of the previous top ridges, therefore keeping the top height of the extension unchanged. This is very similar from an architectural point of view and planning perspective as adding large flat roof dormer windows.
No change of use is proposed in this planning application, only alterations in the external envelope, while not increasing the height of the existing structure.