A door from a home leads out to a deck, where does the mezuzah go? On the right going out, or the right coming in from the deck?
I understand that the deck is like a balcony/porch, which is unroofed. If the deck is enclosed, meaning that it doesn’t serve as an alternative entrance to the house, then the mezuzah should be placed on the right of the door as one leaves onto the deck. If the deck serves as an alternative entrance into the house, the mezuzah should be placed on the right side coming into the house.
Sources: See Taz, Yoreh De’ah 289:4; Chazon Ish 169:2; the common custom is as mentioned in the answer, following the ruling of the Chazon Ish only when the deck (balcony) serves as an entrance.