I have an unroofed large balcony on my upper floor with a single doorway. Is a mezuzah needed, and if so, on which side of the doorway should it be placed?
In general, if the doorway has two doorposts and a lintel it would need a mezuza, If you can send us a picture, I would prefer that, because with Hilchos Mezuza it is best to actually see the doorway in order to prevent mistakes. Regarding the correct side to place the mezuza, with the assumption that it is not possible to get to the balcony from the street, and therefore the only way to enter the balcony is from the apartment, the mezuza would be on the right side of the door when going out to the balcony. If the balcony is smaller than 4×4 amos then the halacha might be different.)
Taz Y:D 289-4 in the name of Maharil, Beis Meir Y:D 289, Chavas Daas brought in Bais Meir, Chovas Hador 8- ftnt. 6 that this is the minhag.