This is interpreted differently by different authorities. Some read it as "the outer covering of those parts of the walls that are within 1m of the boundary should be non-combustible". Others, unfortunately, treat it as "if any part of the building is within 1m of the boundary then all of it needs to be non-combustible". Others yet only consider the elevation facing the boundary. Some want the entire build up of the wall to be non-combustible (not many, in my experience) where most consider the outermost layer only. I've done any number of sand & cement rendered timber frame buildings hard up to boundaries, for instance. The cementitious fake feather-edge boards have been a godsend in these circumstances, because the authorities around here are quite happy for those to be on the boundary elevation and timber feather edge boarding to be on the others. I have never had anyone even look at the roof. Windows are the most problematic of all, however, and are universally disallowed on the boundary facing elevation ion those circumstances.
So, I'm afraid I can't give you an answer other than to suggest you ring your local Building Control and ask them how they interpret the rules.