Planning permission required to add window to living room?

The previous owners of our semi-detached house added an extension to the main living room, which means that the living room now has no window or source of natural light. We'd like to add a window into the gable wall, facing the laneway between ours and our neighbours house.
Just wondering if we need planning permission to do so? I've checked Dun Laoghaire-Rathdown Co. Council's planning FAQ's, but it doesn't seem to answer this specifically...

Thanks.

You will need permission for a window to the side or front