The dormer may well be permitted development but accessing the roof to use as a balcony is not.
Roof balcony planning permission.
Architexeter 12 dec 2013 2.
The doors at the rear should have a juliet guarding to prevent use of the roof unless planning permission is given for use of the roof as a balcony which should then have 1 1m high guarding.
The property is listed or within a conservation zone you will almost certainly require planning permission.
In uk the answer would mostly be yes because raised platforms are not permitted developments.
People who would like a balcony also wonder if it will need planning permission.
While constructing a balcony does require planning permission under the town and country planning order our range of balcony windows do not need planning permission.
However if you are completing any further renovations to create a physical balcony or terrace you must contact your local authority to gain planning permission.
The juliet balcony has a floor no matter how slim it will be considered a raised platform and will need planning approval.